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On-line version - Crop and Soil Sciences

1. public procedures Begin growth Daily Growth E End Growth public functions GetTransFrac This model is adapted from the EPIC growth model developed by Williams J R Jones C A amp Dyke P T 1989 and modified by Williams J R 1994 The EPIC crop model was designed to simulate growth for many different crops Each crop has unique values for the model parameters The main differences with the original EPIC crop growth model are e the biomass energy conversion factor is not adjusted by vapor pressure deficit and by atmospheric CO2 level e the nutrient aeration soil strength soil temperature and aluminum toxicity stresses are not simulated GA PS Vorcinn 3 5 TTeor c Manual ANN e winter dormancy and tillage are not simulated The development of the crop is based on the daily heat unit accumulation not on physiology Constructor Init This procedure is called whenever an object of type SE_model is created at run time Its purpose is to initialize the state of the crop model In particular it computes plant_PointILAI and plant_Point2LAI the two parameters of the S shaped LAI vs heat unit curve from two points on the curve read from the input file The Initializer also adjusts the maximum potential LAI plant_MaxPotLAI based on the plant density plant_MaxPotLAI plant_MaxPotLAI compete SCurve plant_PlantDensity yl y2 where y and y2 are the S curve parameters fitted from two points on the c
2. Non active crops receive the default values K 0 TF 1 LA 0 H 0 i e no light intercepted no height no leaves To partition the solar radiation to a crop using the method of Wallace 1995 we first determine fs the fraction when the crop is completely shaded by the other crop with Wallace s equation 6 fs IntFact TF crop_i 1 TF crop_i Recall that IntFact was the running product of the interception fractions so that IntFact TF crop_i is the running product of the interception fractions of all crops except crop crop_i This is then multiplied by the percent captured by the crop in question So fs is the fraction in complete shade the lowest crop gets whatever light is left over after taller crops have intercepted what they can The other extreme is the case where the crop in question shades all other crops then it would receive all the light it could intercept i e its own transpiration fraction here TF crop_i Wallace proposes a simple linear interpolation between these two extremes using the height ratio his equation 10 f H crop_1 sumH Then the fraction of radiation going to the crop is found by interpolation SolRadFrac crop_i fs f 1 TF crop_1 fs and the actual radiation in MJ m is SolRad crop_i SolRadFrac crop_i clim SolRad real_day These two arrays SolRadFrac and SolRad are stored in the competition object and are provided to interested parties i e th
3. K MinLayer NodeDelta MinLayer CP MinLayer GR N MinLayer K MinLayer sim WP MinLayer sim DEva ar AGauss I d FGauss I d WP 1 1 K I 1 NodeDepth I NodeDepth I 1 GR N I K 1 sim WP I 1 12 except at the top node where this is not in the matrix to the left off the diagonal in the top row so is not computed where DP IJ is the change in water potential over one iteration The node soil water capacity term CP kg m7 is calculated as CP I KgFines I sim WN I soil BValue I sim WP I time_step 13 where KgFines I kg m3 converts from volume to mass in a layer fime_step is the time step s sim WN is the simulated water content m3 m3 and soil BValue is the slope of the water release curve which converts the simulated water potential sim WP to a water content GA PS Vorcinn 3 5 TTeor c Manual 10N After each iteration the mass balance error SE kg m2 sl for the whole soil profile is determined by summing the mass balance errors from all the nodes SE SE ABS FGauss I 14 Convergence is determined by checking whether the FGauss I s are sufficiently close to zero When the total mass balance error is less than the allowable mass balance error the procedure is completed 5 5 1 4 Sub procedure Thomas_Algorithm In this procedure the set of equations set up by procedure Jacobian is solved by Gauss elimination and a new set of soil water potential
4. Menu option Scenario Output files Model summary This file is a record of the model procedures input files times of simulation critical events e g dates at each crop growth stage and final simulation output such as crop yield and water budget Its contents may be printed using the menu option e File Print Model summary 3 4 2 2 Daily summary file H File suffix sum Menu option Scenario Output files Daily summary This file contains daily output variables at the dates specified in the output specification Its contents may be printed or graphed using the menu options e File Print Daily Summary e Graph Daily Summary To see the variables included in this file and their output formats see source file simio pas procedure save Sum data along with the appropriate variable definitions in global pas This file is read and printed by procedures printSum of source file printout pas GA PS Vorcinn 3 5 TTeor c Manual IR 3 4 2 3 Hourly summary files File suffixes e lay soil layers e sof soil flux e plf plant flux e CH climate flux Menu option Scenario Output files Soil layer hourly e Scenario Output files Soil flux hourly e Scenario Output files Plant flux hourly e Scenario Output files Climate flux hourly These files contain output variables at each hour specified in the output spec
5. DUL I KgFines I 2 GA PS Vorcinn 3 5 TTeor c Manual HA where WS I DUL IJ is the volume of water that can be contained in a layer above field capacity KgFines kg m2 converts from volume to mass and Profile_SWCON is a fraction on 0 1 that controls the rate of saturated flow Since the fraction is always less than 1 equation 2 implies that only a part of the water above field capacity drains in each time step This static fraction was computed in the module initialization Tipping Bucket Init The higher this fraction the quicker is the drainage With this fraction we can proceed to calculate the updated water content and the flux out of this layer by sim WN I WS I Drain sim WUptake I time_step KgFines T 3 Flux I Flux I Hold Drain 4 where sim WUptake kg m2 sl is the rate of water uptake from this layer by plants calculated by one of the plant water uptake models earlier in the time step The previous water content W does not appear in equations 2 and 3 because it was already taken into account in the computation of Hold in 1 Note that the new water content will be a bit below saturation and the flux out of the layer will be the same as the flux in less the additional amount the layer can hold plus the same amount of drainage that caused the new water content to be below saturation If the flux into the layer is less than the amount the layer can hold fl
6. real_day transition _day FlagLeafOut 14b The transition_day and maximum LAI are both set in the GrowthStages function when the FlagLeafOut growth stage is entered Once booting is complete the decline continues at a rate of 5 5 of the LAI at booting per day LAI LAlatBooted 0 03 real_day transition_day Booted 14c The transition_day and LAI on which to base the decline are both set in the GrowthStages function when the Booted growth stage is entered Private procedure Yield This procedure is called at the end of each day during grain filling to compute the amount of new grain dry matter produced during the day and the change in the labile carbon reserve It is very similar to the Dry Matter Accumulation procedure with the difference that the carbon sink is the grain and it is assumed that there is no root or shoot growth GA PS Vorcinn 3 5 TTeor c Manual AS First the net photosynthesis NetPS kg m2 is computed from the daily photosynthesis SumPS g m2 exactly as in the late vegetative stages NetPS 0 80 12 44 SumPS 1000 1 Next the daily potential grain growth GrainGrowth kg m2 is determined from a constant maximum daily growth of each grain GrainGrowthMax kg grain dl of 2 2x10 6 kg grain d the number of grains per unit area GrainNumbetr grains m2 and a temperature correction TFGG as GrainGrowth GrainNumber GrainGrowthMax TFGG 2 where this t
7. Before distributing the precipitation it is decreased by any simulated runoff In the initialization procedure the rainfall hours are transformed into a partitioning factor rain_fac which is the proportion of the daily rainfall to apply in each of the time steps when water is to be applied Then during each time step if the time step is one in which water should be applied the rate of application WInput kg m2 sl to the top layer of the soil MinLayer during the time step is calculated as WInputMinL ayer rain_frac clim precip real_day SumRunoff GA PS Vorcinn 3 5 TTeor c Manual 237 where Precip is the daily precipitation and SumRunoff is the simulated daily runoff both expressed as kg m or mm of water WInput is now available for the various soil water procedures as the upper boundary rate 5 3 Vapor exchange evapotranspiration GAPS includes four methods for computing potential evapotranspiration ETP Selecting between them is primarily on the basis of input data availability In addition a shared module partitions potential ETP into actual evaporation and transpiration 5 3 1 Priestley Taylor Priestley and Taylor 1972 developed an equation for calculating potential evapotrans piration ETP for short vegetation well supplied with water under non advective conditions This equation incorporates a proportionality factor known as the Priestley Taylor factor ALPHA which is multiplied by equi
8. S PSSun TempFac TempCoeff PARSun TempPower 8 PSShade TempFac TempCoeff PARShade empPower 9 Because of the way the factor coefficient and power are constructed photosynthesis is somewhat less than PAR Crop photosynthesis for the hour PS g m2 1s then obtained by multiplying the photosynthetic rate for sunlit leaves PSSun g m sh by the sunlit leaf area index LA Sun and adding to this the photosynthetic rate for shaded leaves PSShade g m2 sly multiplied by the shaded leaf area index LAlShade this rate then being multiplied by the time steptime_step s to obtain a quantity PS PSSun LAISun PSShade LAIShade time_step 10 In the final section of this procedure a non stressed stomatal resistance to vapor loss is calculated for both shaded and sunlit leaves using Ohm s equation to model CO diffusion from the atmosphere into the leaves PSxxx COext COint RACO RESxxx 11 where xxx refers to either Sun or Shade ResSun is the sunlit stomatal resistance to water vapor transfer s m 1 ResShade is the shadelit stomatal resistance to water vapor transfer s m 1 COext is the atmospheric CO concentration 0 54 g m 3 COint is the CO2 concentration internal to the leaf assumed here to be 0 20 g m 3 RaCO is the leaf boundary layer resistance to CO transfer PSSun is the photosynthesis rate of sunlit leaves g m 2 s 1 and PSShade is the photosynthesis rate of shadelit leaves g m 2 s
9. X3 1b where X1 X2 and X3 are calculated in the object constructor Init as X1 Min 0 2341 plant RowSpacing 67 9915 100 2 X2 0 0010 plant RowSpacing 0 322 3 X3 In X1 100 0 7675 X2 4 where plant RowSpacing is the distance between plant rows cm In growth stage 4 the transmitted PAR is computed as PctTrans 70 1 exp 0 612 LAT 5 and in growth stage 3 PctTrans is interpolated from that computed in formulas 1 and 5 for the first 7 days in stage 3 after which it is simply that computed by 5 The interpolation formula is PctTrans PctTrans PctTrans PctTrans5 DaysIn3 7 6 where DaysIn3 is the number of elapsed days in growth stage 3 In all growth stages PctTrans is at least 5 Knowing the percent transmission and the portion of the daily solar radiation clim SolRad intercepted by this crop function MySo Rad MJ m2 the daily PAR PARInr MJ m7 is computed by SORKAM equation 34 as PARInt 0 45 TheCompModel MySolRad MyCropl 1 PctTrans 100 7 GA PS Vorcinn 3 5 TTeor c Manual RI Next a temperature stress coefficient Tempco on 0 1 no full growth is determined from the daily mean temperature MeanTemp C as follows MeanTemp lt 5 0 no growth MeanTemp gt 5 amp MeanTemp lt 25 0 05 MeanTemp 0 25 MeanTemp gt 25 amp MeanTemp lt 40 1 full growth MeanTemp gt 40 amp MeanTemp lt
10. default 25 SatWaterCon s default 1 gt if 1 value is replaced by 1 BulkDensity PartDensity CoarseFrag s default 0 LowBound BulkDensity PartDensity HydCon AirEntryPot BValue InitWater DUL DLL InitSoilTemp Clay Silt 0 01 1 2 2 6 0 003 0 3 7 8 1 0143 01 20 25 25 0 03 1 2 2 6 0 003 0 3 7 8 st H SEAN 20 25 25 0 08 1 2 2 6 0 003 0 3 7 8 0 3 0 1 20 25 25 0 15 142 2 6 0 003 0 3 7 8 1 0 3 0 1 20 25 25 Plant file plant def GAPS 3 0 plant file with the default values The plant file must be saved with the extension PLT Lines starting with the sign are ignored at input Comments added after the input data preceded by a are also ignored Se oS AE OSE SE OSE SE s single i integer b boolean s70 string 70 GA PS Vorcinn 3 5 TTeor c Manual 137 Global variables Lo to crop options 0 None 1 amp 0 Stockle Riha 1 amp 1 Stockle Riha maize 1 amp 2 wheat 1 amp 3 tree 2 amp 0 Sorkam 2 amp 1 Sorkam temperate 282 tropical 3 amp 0 Epic 4850 Constant 0 proc _status 1 gt Canopy water interception 0 proc _status 2 gt Critical leaf water potential 0 proc_status 3 gt 0 proc_status 4 an n 0 proc_status 5 gt 0 proc_status 6 gt 0 proc_status 7 Se e 0 proc_status 8 u 0 proc_status 9 gt loaded in croplib crop model Init GENERIC crop PlantName s70 1 crop SowingDate 1 a
11. s has_matured function It follows the empirical formula of Gerik et al 1988 A variable used only by this procedure GrainDryingET kg m2 accumulates the potential ETP since grain drying began at maturity GrainDryingET GrainDryingET sim PotET 1 This sum is used to decrease the maximum grain moisture i e at the beginning of maturity GrainMoistureMax kg water kel grain dry matter assumed to be 48 by the empirical formula GrainMoisture GrainMoistureMax exp 0 00591 GrainDryingET 2 5 4 2 Crop model Stockle Riha source file stockle pas object name SR_model public procedures Daily Growth Begin TimeStep Growth TimeStep Stress open det file write summary Daily Growth End End Growth PSTempFac public functions m private procedures Water Interception Max Photosynthesis Limit_Photosynthesis Light_Interception Critical Leaf Water Potential Simple Water Stress Dry Matter Accumulation LimitRootingDepth private functions This model is adapted from the simulation model developed by Stockle amp Campbell 1985 to predict the effects of water stress on corn yield and the earlier model by Stockle to predict the effect of water and nitrogen stress on wheat Although there are differences between the two submodels they share a common structure and some common procedure which are grouped in this generic model The generic model can GA PS Vorcinn 3 5 TTeor c Manu
12. s70 saveFileName C GAPS3 EXAMPLE SUM s70 sumFileName C GAPS3 EXAMPLE DET s70 detFileName C GAPS3 EXAMPLE LAY s70 layFileName C GAPS3 EXAMPLE SOF s70 sofFileName C GAPS3 EXAMPLE PLF s70 plfFileName C GAPS3 EXAMPLE CLF s70 clfFileName 1 0 or 1 proc_status 10 gt ETP Priestley Taylor 0 0 or 1 proc_status 11 gt ETP Penman 0 0 or 1 proc_status 12 gt ETP Linacre 0 0 or 1 proc_status 13 gt ETP Pan 0 0 or 1 proc_status 14 gt I 0 or 1 proc_status 15 gt Flow Richards Eq 0 0 or 1 proc _status 16 gt Flow Tipping bucket 0 0 or 1 proc_status 17 gt Flow Matrix flux pot 1 0 or 1 proc _status 18 gt Uptake Pot driven 0 0 or 1 proc _status 19 gt Uptake Plant avail 0 0 or 1 proc _status 20 gt Field hours 0 0 or 1 proc_status 21 gt Input Runoff 0 0 or 1 proc _status 22 gt EPIC water uptake 0 0 or 1 proc_status 23 gt 0 0 or 1 proc _status 24 gt 0 0 or 1 proc _status 25 gt 0 0 or 1 proc _status 26 gt 0 0 or 1 proc _status 27 gt 0 0 or 1 proc _status 28 gt Soil Soil temp 1 0 or 1 proc _status 29 gt Soil Harmonic temp 0 0 or 1 proc _status 30 gt 3600 s 900 92400 s timestep 90 i req first day 365 i req last day 4 1 1 4 run views 14 i 1 40 initviews 1 27 i 1 40 initviews 2 30 i
13. sim WP I 1 A N NodeDelta I GR sim K T 2 Once we no longer need the difference between old and updated water contents the old water contents for the next time step are set equal to the new ones from this step sim WN I WII 3 and the rate of drainage from the lower boundary of the soil profile Drain_Rate kg m sh is calculated assuming no matric potential induced flux at the bottom of the soil profile as Drain Rate GR K LastLayer 4 where GR is the acceleration of gravity 9 8 m Sc and K LastLayer is the hydraulic conductivity of the bottom layer of the profile kg s m3 This equation shows that we assume that the only force on the water in the bottom layer is gravity downwards Clearly this relation would have to be modified for soils within the influence of a water table 5 5 2 Tipping bucket source file soillib pas procedures Tipping Bucket Init Tipping Bucket Tipping Bucket Done This module uses the soil water flow approach contained in the CERES Maize model Jones and Kiniry 1986 The code from the CERES Maize was translated into Pascal without altering the general computational method In addition a soil evaporation routine was added by D Rossiter to allow for evaporation from near surface layers below the top soil layer GA PS Vorcinn 3 5 TTeor c Manual 1A As the name of this procedure suggests the soil is conceptualized as consisting
14. 0 39 3200 1 00 0 00 0 00 0 35 3200 1 00 0 00 0 00 0 56 3200 1 00 0 00 0 00 2 33 3200 1 00 0 00 0 00 2 72 3200 1 00 0 00 0 00 10 00 3200 1 00 0 00 0 00 LLL 3200 FS Oe 000 11 61 3208 0 73 08 27 0200 17 97 3200 1200 0 00 0 00 3 40 3200 0 50 0 49 0 83 7 04 3200 0 50 0 49 0 83 6 7 8 9 10 ES 7 NonstressRes 8 PSStressFac 9 I PSStressfFac 10 LAIStressFac 154 0000000000000 0000000 0000620 0000000 0000000 0000046 0000000 0000000 0000000 0000000 0000000 0000000 0000000 0000000 8 0 0 0 0 0 0 0 0 D 0 0 0 w 0000000 000 495 0000213 0000227 0000278 0001 000 255 027 0002077 0001 258 0000970 000 000 482 119 0000712 9 240 241 239 238 230 213 182 187 221 178 156 171 175 10 Climate flux example clf 1 50 0 0000344 10 50 0 0000545 20 50 0 0000434 30 50 0 0000409 40 50 0 0000571 50 50 0 0000773 60 50 0 0000563 70 50 0 0001052 80 50 0 0001621 90 50 0 0001797 00 50 0 0001593 10 50 0 0000783 20 50 0 0003694 30 50 0 0002115 40 50 0 0003149 50 50 0 0002550 60 50 0 0001969 70 50 0 0003917 80 50 0 0001633 90 50 0 0002077 200 50 0 0001697 210 50 0 0001311 220 50 0 0001482 230 50 0 0002116 240 50 0 0001311 1 2 decimal_day sim ETP sim ActEva sim ActTrans sim Heatflux AirTemp sim NetRad NOD GS WH Fa OO OCH ECH CO CH EH CH CH CH CH CH CH CH e C O COO 0 0 GOW 0000344 00
15. 45 0 2 MeanTemp 9 MeanTemp gt 45 0 no growth 7 In growth stage 4 this coefficient is further adjusted by SORKAM equation 35 for the effects of high minimum temperature i e warm nights during grain filling where clim MinTemp gt 19 C Tempco Min Tempco 0 0333 clim MinTemp real_day 1 633 8 This temperature stress coefficient and the water stress coefficient Watco which was computed in the water stress function are compared and the numerically lesser i e more stressed one is chosen as the stress factor StressIndex on 0 1 Then the daily top dry matter can be computed by SORKAM equation 36 as DailyTopDryMatter Alpha PARInt StressIndex 103 9 where Alpha is an empirical conversion from MJ to g of dry matter a constant 3 2 g MJ land the factor of 103 converts from gtokg This is then accumulated into AccTopDryMatter kg m2 Private Procedure daily plant _growth This procedure is called at the end of each day from emergence to the end of grain filling to grow the sorghum plant It is based on SORKAM procedure GROW but has been simplified here we do not grow individual leaves and do not partition photosynthate into plant organs other than the top root and grain First a fractionation stage 1 4 is determined from the growth stage and the number of elapsed days in stages 2 and 4 These are then used to partition the top dry matter DailyTopDryMatter determined in p
16. The mass balance should be zero but unless both the net photosynthesis and C reserve are initially zero this is very unlikely from a direct computation of 6 What must occur is that Reserve is adjusted until the equation balances Thus FRes is a function on Reserve and can be solved by the Newton Raphson method of root finding First the derivative of the function with respect to Reserve is computed as dFRes ParallelDemand Reserve 1 Reserve ShootSaturation 1 Reserve RootSaturation 8 and the new value of Reserve is computed as the intercept of the tangent to the function i e the line with the derivate as its slope with the Reserve axis Reserve Reserve FRes dFRes 9 This estimate of Reserve is then substituted into equations 6 and 7 and a new estimate is obtained by application of equation 9 The process stops when the mass balance error FRes is within 1ppm of 0 and the residual mass balance error is added into the new estimate of the reserve which is then assigned to CRes With the revised C reserve value CRes obtained by mass balance the actual shoot and root growth are computed as ShootGrowth ShootDemand 0 42 CRes CRes ShootSaturation 10a RootGrowth RootDemand 0 42 CRes CRes RootSaturation 10a where the 0 42 factor is the same as for equation 5 The actual growths are accumulated into the appropriate dry matters GA PS Vorcinn 3 5 TTeor c
17. The model then queries each crop model for its current LAI actually it directly accesses a field in the object which is not the preferred object oriented approach we should really use an access procedure LA crop_i TheCrop crop_1 LAI The competition model assumes that each crop model expresses light interception by Beer s law although in fact there are variations For example the Stockle model uses a polynomial function of LAI and SORKAM uses a square root function However at any given LAI the same light interception could have been obtained from a Beer s Law equation with an appropriate k So to get all crop s interception on the same basis we can calculate the presumed k If we assume that GetTransFrac has the form 1 exp k LAI i e 1 GetTransFrac exp k LAD we can now back calculate what k would have had to be to obtain the observed interception fraction K crop_1 In TF crop_i LA crop_i The model queries each crop model for its current canopy height using an access procedure and keeps a running sum of the heights 4 The GetTransFrac access function is defined as a virtual object method in the generic crop model which implements it as a simple Beer s Law function of LAI So any crop model that can accept this function and which models LAI need not over ride the virtual method GA PS Vorcinn 3 5 TTeor c Manual 04 H crop_1 TheCrop crop_i GetHeight sumH sumH H crop_1
18. The winter_kill_factor is the product of the kill_snow and kill_temp factors It is set to zero when either kill_snow or kill_temp is less than 0 05 The winter_kill_factor is then used to reduce AccTopDryMatter AccTopDryMatter AccTopDryMatter 1 winter_kill_factor 5 4 2 3 Crop model Stockle Riha Fast Growing Tree source file stockle pas object name SRt model public procedures Daily Growth Begin Daily Growth End End Growth TimeStep growth TimeStep Stress open det file public functions GetTransFrac PSTempFac is active is transpiring private procedures Dry Matter Accumulation Winter kill Light Interception LimitRootingDepth Critical Leaf Water Potential This submodel uses its ancestor the generic crop model Stockle Riha as a framework for modeling the growth of fast growing perennial plantation trees In order to account for the differences between a densely planted annual grain crop and a widely spaced perennial woody plant which remains in the vegetative phase many procedures are unique to this submodel The primary processes of interest are partitioning between wood leaves and roots and root dynamics in the soil profile Rather than using a growth stage concept as is key in the maize and wheat models the fast growing tree modelled here remains in the vegetative phenological phase from planting until harvest Respiration is modelled explicitly and both root and leaf turnover are
19. sec default 43 200 and Time is the time of the day sec To determine solar noon accurately for a particular geographic location see Gates 1980 Appendix 4 p 572 The sine of the solar declination angle So DcA can be computed according to Swift 1976 as SolDcA 0 39785 sin 4 869 0 0172 JulDay 0 03345 sin 6 224 0 0172JulDay 3 where JulDay is the day of year number or Julian date i e January 01 1 December 31 365 Solar elevation angles are calculated for every time step of the day and if the angles are positive the theoretical solar radiation for the hour is calculated On a daily basis SolarAngle Daily estimates the total theoretical solar radiation for the day SpaceSum This value is needed to estimate the fractional cloud cover in procedure AtmosTrans 5 2 3 Distribution of precipitation over the day source file rainlib pas procedures Distribute Precipitation Distribute Precipitation Init This module allocates the daily precipitation and or irrigation specified in the climate input file Two variables contained in the location input file determine during which time interval water will be applied FirstRainHour and LastRainHour For example to apply all the daily precipitation within one hour starting at 6 00 pm specify FirstRainHour 18 and LastRainHour 19 Any application of water according to the climate file can be altogether withheld by setting FirstRainHour LastRainHour
20. sim WN I NodeDelta I 4 where NodeDelta m is the distance from this node to the one above it Dividing by this factor converts the conductivity into a conductance Heat fluxes are calculated by applying the equation of continuity to the Fourier law CP d SoilTemp dt d K d SoilTemp dz dz 5 where z is the node depth The numerical solution to this equation is similar to the solution of the water flow problem by the Richards Equation First a tridiagonal matrix representing the heat balance is formed in the procedure Jacobian and then solved by elimination and back substitution Since the conductances and capacitances are not a function of the driving force as is the case in the water flow problem where the hydraulic conductivity is a function of the soil water potential and content no iterations are needed to find the correct solution for the new soil temperatures After a new set of soil temperatures is calculated procedure Calc_Fluxes calculates the heat flux sim HeatFlux W m2 sly across the soil surface positive downwards from the thermal conductance of the surface node K MinLayer 1 W m kh and the gradient between the air and first soil layer at the end of the previous time step sim SoilTemp MinLayer 1 sim SoilTemp MinLayer and at the end of this time step TN MinLayer 1 TN MinLayer as sim HeatFlux K MinLayer 1 1 loca F sim SoilTemp MinLayer 1 sim SoilTemp MinLayer loc
21. this is initialized to zero Thereafter if the estimate of water uptake from 4 exceeds the available water in the layer if WUptake time_step gt LayerAvail i then 5 In this case the water uptake is limited to the plant available water and the portion of the transpiration demand that could not be satisfied by this layer is passed to the next layer down as the AdditionalDemand kg m 2 WUptake LayerAvail i time_step AdditionalDemand sim WUptake time_step LayerAvaill i 6 The crop s active transpiration is accumulated as well as the total uptake in the layer TheCrop crop_i ActTrans TheCrop crop_i ActTrans WUptake sim WUptake layer sim WUptake layer WUptake Finally the available water in a layer is reduced by the amount just taken up LayerAvail layer LayerAvail layer WUptake time_step leaving less water for the next plant Note that after following this algorithm for the entire rooting profile there may be some unsatisfied demand This will be the difference between actual and potential transpiration for the crop The entire process is repeated for subsequent active crops GA PS Vorcinn 3 5 TTeor c Manual 1 N 5 7 3 EPIC model water uptake This procedure is based on the wateruse model as outlined in the EPIC Erosion Productivity Impact Calculator model documentation Sharpley and Williams 1990 It is similar to Plant available water uptake with two
22. 1 40 initviews 3 35 i 1 40 initviews 4 GAPS Vorcinn 2 5 Tleer s Manual AR Printout of input files Climate file printout climate txt GAPS Climate Input Data Climate Data File Name C GAPS3 EXAMPLE CLI ClimateFileNam es Climate Name CMN11000 cli clim climateNa me Report Date 5 24 1994 date Report Time 10 42 5 time Air Air Solar Day Temp Temp Rad Rain Rel Pan Vapor Snow of max min MJ fall Humidity Wind Evap Dens cm Year Celsius m2 day mm d fraction m s mm d g m3 1 O 122 5 4 0 0 44 5 SoS 0 0 ee 0 0 2 tno 4 3 Le oma 41 2 Soo 0 0 Greg 0 0 3 0 8 14 6 Ze 2 8 64 2 sise 0 0 saka 0 0 4 3 3 18 8 4 4 03 62 0 Fe 0 0 Pan 0 0 5 6 0 1149 4 3 1 43 342 TOSA 0 0 ae 0 0 6 Fu CES 4 6 327 67 2 0 0 aaa 0 0 E 2 Lo 6 0 0 1 62 1 en 0 0 n 0 0 8 443 S169 5 8 0 0 5042 sen 0 0 Bar 0 0 9 200 948 E 0 0 50 4 2n 0 0 seniz 0 0 10 1 0 14 3 7 2 0 0 49 5 FAAS 0 0 sn 0 0 361 6 471525 4 9 0 0 72 8 0 0 ies 009 362 20 1808 De de 0 0 62 4 Ra 0 0 aa 0 0 363 LAO Lado 4 4 0 0 62 4 HASH 0 0 See 0 0 364 8 0 14 7 SL 0 0 60 8 0 0 ae 0 0 365 SIT EZ 10 5 0 0 60 2 ARE 0 0 Bae 0 0 1 2 3 4 5 6 7 8 9 10 1 day 2 clim MaxTemp day 3 clim MinTemp day 4 clim SolRad day 5 clim Precip day 6 clim RelHumid day 7 clim WindSpeed day 8 clim PanEV day 9 clim VaporDensity day 10 SnowPack day GA PS Vorcinn 3 5 TTeor c Manual 140 Location file printout location txt GAPS Lo
23. 3420 0 0007 170 56 0 00 200 34 1 991 1 764 0 227 0 000 240 3486 OST Deal 35557 1479 05 00 2 10 0 00 175 61 0 00 117 49 2 177 1 937 0 240 0 108 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 real day 7 sumDrain 13 SumNetRad 19 GDD 2 sim PoTET 8 Sumwcchange 14 AccTotalDryMatter 20 LAI 3 sumPotEV 9 SumWI 15 AccTopDryMatter 21 RootingD 4 sumev 10 ProfileWater 16 AccRootDryMatter 22 AccStres 5 sumPotTrans 11 ProfileAvail 17 AccYield 23 SumPs 6 sumActTrans 12 NetHeatFlux 18 AccDD 24 SumField Soil layer example lay 3 soil LastLayer 97 50 0 050 0 324 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 0 98 50 0 050 0 324 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 0 99 5 0 0 050 0 324 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 0 00 50 0 400 0 373 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 0 01 50 0 445 0 403 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 0 02 50 0 426 0 417 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 Ove 03 50 0 163 0 324 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 0 04 50 0 050 0 324 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 AS 05 50 0 050 0 324 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 0 06 50 0 050 0 324 17 17 0 0E 0000 0 0E 0
24. 365 crop HarvestDate 1 a 1500 crop RootWP s J kg 0 0020 crop RootRad s m 2 5E 0010 crop RootRes s m4 kg s 2 crop FRoot 1 1 19 crop NRoot Ci LJ 20000 crop RootDens 2 s m m3 for n FRoot to NRoot 20000 crop RootDens 3 20000 crop RootDens 4 20000 crop RootDens 5 20000 crop RootDens 6 20000 crop RootDens 7 20000 crop RootDens 8 20000 crop RootDens 9 20000 crop RootDens 10 20000 crop RootDens 1 20000 crop RootDens 12 20000 crop RootDens 13 20000 crop RootDens 14 20000 crop RootDens 15 20000 crop RootDens 16 20000 crop RootDens 17 20000 crop RootDens 18 20000 crop RootDens 19 1 50 crop CanopyHeight s m 30 crop RA s s m 20 crop RCopen s s m 0 75 crop AS s Main crop object variables loaded in croplib crop model Init 0 00 plant LAI s 0 00 plant InitialDryMatter s kg ha 1 20 plant MaxRootingDepth s m 0 025 plant SowingDepth s m variables only for Stockle Riha crop model 2 00 plant _CanopyMax s kg m2 1500 plant_CriticalLeafWP s J kg 62500 plant_PlantDensity s pl ha 0 500 plant_HarvestIndex s 570 plant_Kernels_per_plant i 8 plant Kernel growth rate i mg d Riha 7 0 plant _CLWP Power s GA PS Vorcinn 3 5 TTeor c Manual 122 only for Stockle 1 0 plant_Pmax s mgCO2 m2Leaf sec model 0 00
25. 4 It can simulate a sequence of crops and climates in a single simulation run 5 It can be run on any personal computer with a hard disk or high capacity diskette which uses the MS DOS operating system 6 A batch version with the same simulation procedures but a command line user interface can be used for large numbers of repetitive simulations and easily integrated with other computer programs for data entry output or analysis 7 Version 3 5 is able to model plant competition GAPS is intended for use in research and especially in teaching the principles and practice of dynamic simulation modelling of the soil plant atmosphere system We assume that GAPS users have some background in such models or are using GAPS in conjunction with other instructional materials on simulation in general and the environmental processes being modelled in particular This manual is organized as follows Chapter 2 explains how to install GAPS on your system Chapters 3 and 4 describe how to run interactive and batch GAPS Chapter 5 explains the scientific basis of each model procedure in the simulator Chapter 6 has some notes of interest to programmers The manual concludes with a bibliography Appendix A discusses the most common error messages A list of the content of the distribution diskettes is given in appendix B Appendix C contains examples for each input and output file with comments A flowchart of the program is presented in appendix D Appen
26. 52 0 44 0 0 167 7 0 86 0 74 0 0 132 4 1 35 1 18 0 0 140 0 1 78 1 57 0 0 2003 1 99 1 76 0 0 11745 2 18 1 94 12 13 14 15 SumNetRad AccTotalDryMatter AccTopDryMatter AccRootDryMatter AccYield AccDD 18 00 SI 10 10 00 99080 O O O OOO TOO OOO OO 19 20 21 22 23 24 WIn Wat_P AvailP HeatF NetRad TotDM TopDM RootDM Yield ACC mm 0 00 Os 0 00 0 0 00 0 0 00 0 0 00 0 0 00 0 0 00 0 0 00 0 0 00 0 0 00 0 0 00 0 0 00 0 0 00 0 0 00 Le 0 00 4 0 00 6 0 00 8 0 00 14 0 00 19 0 00 23 0 00 29 0 00 35 0 00 40 0 00 46 0 11 52 17 H GDD LAI RootingD AccStres SumPS SumField Day PRPRPRPRPP I 10 10 10 10 10 10 10 20 20 20 20 20 20 Hour Layer WN m3 m3 PR PRY NNNNNNNNNNNNNNNNNNNDHND hp Ann RUNON AUN BRUNON ODUNDAN 6 2 9 2 9322220932 II D Es 245 283 283 283 213 21 8 218 043 277 283 283 a2 hs 218 218 045 244 283 283 273 218 WP J kg 3 3 3 3 3 3 3 3 3 3 11 SPL 3 3 3 3 3 Sd DD DIO Ss OO NINO IE IE Note that WFlux and WUptake are 1 Gs amp Nh 2 3 day hour layer sim WN layer sim WP layer Soil flux soilfl txt SOF Data File Name Date Time Day Hour ETP J 12 0 123 10 2 0 196 20 2 0 156 30 2 0 147 40 2 0 205 50 2 0 278 60 2 0 202 70 2 0 378 80 2 0 583 90 2 0 646 100 12 0 573 110 12 0 281 120 2 1 329 130 12 Us TOL 140 12 1133
27. 90 2 gt 9 3957 m3 m3 For a loamy sand a more appropriate suction would be 40cm and again applying equation 1 with parameters for this textural class we obtain a critical moisture content of SM 0 439 e0 0330 In 40 2 gt 0 2802 m3 m3 Complications If the Tipping Bucket water flow method is used to estimate soil water content a problem may arise when estimating field hours if a plant is not actively growing This is because in the Tipping Bucket method water flow upward is not modelled The only ways in which water can leave a profile are 1 drainage 2 plant water uptake and 3 near surface evaporation If a plant is growing this is usually a good approximation to reality as the plant pumps water from the profile at a much faster rate than could be achieved by evaporation from the surface and upward movement from lower layers However if the plant is not growing e g in early spring only evaporation can sufficiently dry the upper soil to allow workability assuming that the critical limit for workability is higher than the drained upper limit The complication is that the GAPS tipping bucket routine only evaporates in the top few cm usually less than the depth of tillage see the description of the Tipping Bucket method for a description of how to GA PS Vorcinn 3 5 TTeor c Manual 112 determine the depth to which evaporation is effective Thus the layers between the depth of evaporation and tillage can t dry
28. C N ratio of the grain to a constant 13 GrainNumber GrainNumber GrainGrowth CFracGrain CNRatioGrain 4 Private procedure Max_Photosynthesis Both sunlit and a shaded rates of photosynthesis PSSun and PSShade g m2 sh are then calculated assuming that photosynthesis is related to PAR according to an equation given for maize by Hesketh and GA PS Vorcinn 3 5 TTeor c Manual AB Baker 1969 This rate is then modified for leaf temperature using a temperature factor TempFac which is obtained by calling the correct virtual procedure for the submodel The code TempFac PSTempFac AirTemp calls one of the virtual functions e g SRw_model PSTempFac for wheat which returns the temperature factor See the submodels for a description of the computation of the temperature correction factors This factor which depends on leaf temperature is further multiplied by another linear factor that does not vary with temperature TempCoeff This is crop specific and is set by the constructor of each Stockle Riha submodel For maize this is 6 2527E 05 0 7 and for wheat 1 6 2 23583E 05 So the product of the linear factors is on the order of 1 Another crop specific factor is TempPower which is the exponent to which PAR is raised This is set by the constructor of each Stockle Riha submodel For maize this is 0 507578 and for wheat 0 695407 Given these factors PAR is converted to PS by these equations PSSun TempF
29. File Name C GAPS3 EXAMPLE SAV Report Date 5 24 1994 Report Time 10 41 53 Number of hours to save 1 Hour 1 12 Number of days to save 25 Day 13 1 Day 2 10 Day 3 20 Day 4 30 Day 5 40 Day 6 50 Day 60 Day 8 70 Day 9 80 Day 10 90 Day 11 100 Day 12 110 Day 13 120 Day 14 130 Day 15 140 Day 16 150 Day 17 160 Day 18 170 Day 19 180 Day 20 190 Day 11 200 Day 22 210 Day 23 220 Day 24 230 Day 25 240 GA PS Vorcinn 3 5 TTeor c Manual 151 GA PS Vorcinn 3 5 TTeor c Manual 152 Output files Model summary example det GAPS Simulator Starting simulation on 5 24 1994 at 10 40 10 KKKKK Input file names KKEKKKKKKKKKKKKKKKKKKKKK Site C GAPS3 EXAMPLE LOC LocationFileNa me Soil C GAPS3 EXAMPLE SOL SoilFileName Climate C GAPS3 EXAMPLE CLI ClimateFileNam es Plant 1 C GAPS3 EXAMPLE PLT PlantFileNames Save C GAPS3 EXAMPLE SAV SaveFileName KKKKK Output file names KKAXKKKKKKKKXKKKKKXKkX Summary C GAPS3 EXAMPLE SUM Det FileName Model C GAPS3 EXAMPLE DET SumFileName Layer flux C GAPS3 EXAMPLE LAY LayFileName Soil flux C GAPS3 EXAMPLE SOF SofFileName Plant flux C GAPS3 EXAMPLE PLF PlfFileName Climate flux C GAPS3 EXAMPLE CLF C1fFileName KKKKK Simulation procedures KKEKKKKKKKKKK KKK KKK Soil temperature not simulated SoilTem p_method Evapo transpiration Priestley Taylor Priestley Taylor ETP u ETP_met hod Surface runoff not simulated Runoff_ method Soil water
30. GA PS Vorcinn 3 5 TTeor c Manual INR Procedure Calculate_Fluxes At the end of each time step s calculation this procedure is called to calculates the change in profile water content this time step which can be reported in the simulation output as well as to reset the starting water contents for the next time step The rate of change in profile water content WC_Change kg m2 sh is calculated in the obvious way LastLayer sim WN W KgfFines DrainRate i MinLayer 1 WC_Change time step where the term sim WN i W i represents the volumetric difference between the water contents at the end and beginning of the times step m3 m3 KgFines i kg m2 converts from volume to mass per unit area DrainRate kg m2 1s the flux out of the bottom of the profile and time_step converts the mass to a rate The starting water contents for the next time step are reset by WII sim WN I 2 for each layer J 5 5 3 Matric flux potential source file soillib pas procedures Matric Flux Potential Init Matric Flux Potential This is a close variant of the Richards equation The difference is that this procedure uses matric flux potentials instead of water potentials to compute the potential gradients that drive water flow In the initialization procedure Matric Flux Potential Init reference values for the matric flux potentials in the situation when the soil is equilibrated at the air entry
31. GAPS GAPS will not display any run time graphs if this environment variable is set GA PS Vorcinn 3 5 TTeor c Manual A 2 5 Updating input files The format of all the input files sol cli loc plt sav amp set has changed with the new release of GAPS Old input files except soil files from versions older than 2 1 can be updated to the new format with the conversion program convert exe The wildcards and can be used to specify a group of files Only the files in the current directory can be updated A backup of the old input file will be saved under the same filename with extension k Examples To convert all the input files in the current directory type the following command at the DOS prompt convert To convert all the plant files in the current directory type convert plt To convert all the input files starting with tut2 type convert tut2 GA PS Vorcinn 3 5 TTeor c Manual 5 3 Running GAPS This chapter describes how to use interactive GAPS 3 1 Starting GAPS GAPS is invoked from the DOS command line like any other executable program with the command syntax drive path gaps exe filename set When GAPS starts up the simulation parameters are initially null no procedures no input or output files no graphs unless a scenario file is specified at the command line 3 2 Interacting with GAPS The GAPS interface has three visible components the m
32. J ke is calculated as GA PS Vorcinn 3 5 TTeor c Manual 52 LeafWP RootWP ActTrans LeafRes 5 where RootWP is the root water potential calculated in the module WaterUptake J kel and LeafRes is the leaf resistance to liquid water transport m4 sl kg and is assumed to be 2 x 100 Campbell 1985 Finally the ratio of actual to potential transpiration sim TRatio dimensionless is calculated using the adjusted value of actual transpiration from the preceding parts of the procedure as sim TRatio sim ActTrans sim PotTrans 6 Private procedure Simple_Water_Stress This procedure is called at each time step to compute the stress coefficient PSStressFact if the Critical Leaf Water Potential simulation option was not selected by the model user The stress factor is set equal to the transpiration ratio TRatio of the actual transpiration rate ActTrans kg m sh to the potential transpiration rate PotTrans kg m2 sh which is calculated in the time step procedures of the simulation driver sim TRatio sim ActTrans sim PotTrans 1 Private procedure LimitRootingDepth This procedure is called by submodels once they have determined a proposed rooting depth to adjust this depth for two things sowing depth and the user defined maximum First the rooting depth predicted by the submodels is increased by the sowing depth specified in the plant input file RootingDepth RootingDepth plant SowingDepth
33. Matric Flux Potential or soil moisture content Tipping Bucket below which the soil is considered dry enough These parameters are supplied by the GAPS user as entries in the location loc input file The user must supply values for both tillage e g plowing disking and traffic e g sidedressing harvesting GAPS will apply the values for tillage when there is no active crop i e before planting and after harvesting under the assumption that the farmer s primary workability consideration in this period is tillage When there is an active crop GAPS will apply the values for traffic How does the model user determine values for the parameters Determination of the depth to which the soil must be dry enough is fairly simple it is the deeper of 1 the depth to which the soil will be worked by an implement e g plow to 20cm and 2 the depth to which the soil can be significantly compacted by the power source tractors draught animals etc The implement depth is set by the farmer and of course is zero for traffic only as opposed to tillage The depth of compaction should ideally be determined by field observation with a instruments such as the penetrometer This can be estimated from physical principles see e g Hillel 1980 if the machine weight and design are known A reasonable approximation is to use the depth of the plow layer or surface soil as observed in the field typically 15 to 20 cm f
34. Matric Flux Potential Adjacent thick layers especially with l See section 7 1 Changing GAPS limits for information on how to increase the number of allowable layers GA PS Vorcinn 3 5 TTeor c Manual 13 contrasting saturated hydraulic conductivities or moisture release curves may lead to instability in the numerical methods during periods with highly contrasting water contents e g infiltration into a dry soil In this case you will get an error message Non convergence of iterative solution To avoid this specify thin layers 1 to 2 cm thickness around the boundary between contrasting layers The most common problem with non convergence occurs at the surface where infiltration and evaporation are most active We highly recommend specifying layers of increasing thickness at the surface e g of lcm 2cm and 5cm even if the surface is actually homogeneous to some greater depth as is typical of cultivated soils The thickness of the surface layers is also important when estimating field hours The depth to which you specify that the soil must be workable see location file description should correspond to the lower boundary of a soil layer Root growth in GAPS is entirely by layer when the model predicts that the rooting depth has exceeded the lower boundary of a layer the roots instantly fill the next layer So for realistic water uptake the layers should be thin enough so that this is not a bad
35. O 1985 Simulation of the effect of water and nitrogen stress on growth and yield of spring wheat Ph D thesis Washington State University Pullman Stockle C and G S Campbell 1985 A simulation model for predicting effect of water stress on yield an example using corn Adv in Irrigation 3 283 323 Swift L W 1976 Algorithm for solar radiation on mountain slopes Water Res 12 108 112 Tanner C B and W A Jury 1976 Estimating evaporation and transpiration from a row crop during incomplete cover Agron J 68 239 243 Thornley J H M and I R Johnson 1990 Plant and Crop Modelling Oxford University Press Oxford UK USDA Soil Conservation Service 1972 National Engineering Handbook Hydrology Washington USDA SCS Wallace J S 1995 Towards a coupled light partitioning and transpiration model for use in intercrops and agroforestry pp 153 162 in Sinoquet H and Cruz P Ecophysiology of tropical intercropping INRA Paris Weaver H L 1984 A mechanistic model of evapotranspiration from Saltcedar Ph D thesis Pullman Washington State University Wilkerson G G J W Jones K J Boote K T Ingram and J W Mishoe 1983 Modeling soybean growth for crop management Transactions of the Am Soc of Ag Eng 26 63 73 Williams J R Jones C A and Dyke P T 1989 EPIC Erosion Productivity Impact Calculator 1 The EPIC model Temple TX USDA ARS Wilson J B 1988 A Review of Evidence on the Control of
36. PSStressFact if the Critical Leaf Water Potential simulation option was selected by the model user It is only called whenever there is simulated potential transpiration i e sim PotTrans is greater than zero It uses an empirically derived equation that relates decreases in leaf water potentials to increases in stomatal resistance The increase in stomatal resistance contributes to a simulated decrease in actual transpiration ActTrans below potential transpiration sim PotTrans Using Ohm s Law to model water flow through plants ActTrans RootWP LeafWP LeafRes 1 a new leaf water potential LeafWP J ke based on the simulated actual transpiration is calculated This leaf water potential in turn is used to calculate a new stomatal resistance which then results in a new simulated ActTrans and LeafWP This process is repeated until LeafWP changes less than 10 J kel with successive iterations The details of this iterative process are now presented Initially the saturation vapor density SVD g m3 1s calculated according to Campbell 1981 and the slope of the saturation vapor density function SSVD g m3 Kl is calculated according to Fuchs et al 1978 exactly as in the Priestly Taylor ETP equation Next the stressed stomatal resistance StressRes is calculated following the work of Fisher et al 1981 using values for corn given by Stockle and Campbell 1985 StressRes NonStressRes 1 LeafWP plant Critical
37. TTeor c Manual 74 Data field Variable name Units of Modules in which field is used measure 1 Harvest index plant_Harvest Default 0 31 Daily Growth End Index E plant_MinHI Default 0 15 Daily Growth End index Base temperature plant Base Temp Daily_Growth_End Default 10 0 Optimal plant_Optimum C Daily_Growth_End temperature for Temp growth Default 25 0 5 Potential heat units plant_PotUnits Default 2000 Daily Growth End req for maturation Biomass energy plant _Biomass kg MJ Daily_Growth_End ratio Energy Default 25 0 7 Fraction of season plant Decline Default 0 60 Daily Growth End LAI declines Fraction Maximum plant MaxPotLAI Default 9 0 Daily Growth End potential LAI Ist point LAI vs plant PointILAI Default 0 25 Daily Growth End heat unit curve x1 as fitted by 0 20 fl compete FitSCurv e 2nd point LAI vs plant Point2LAI Default 0 45 Daily Growth End heat unit curve x2 as fitted by 0 80 f2 compete FitSCurv e 11 rate of LAI decline plant LAI Default 1 00 Daily_Growth_End DeclineRate Extinction plant_ExtinctionC Default 0 65 GetTransFrac coefficient oeff 1st point max plant_ MaxPotLAI Default Daily Growth End LAI vs population is adjusted with 10000 0 2 density curve xl this and the next fl field GA PS Vorcinn 3 5 TTeor c Manual JA 14 2nd point max plant_MaxPotLAI Default Daily Growth End LAI vs population is a
38. TTeor c Manual Al Public Function PSTempFac This procedure computes a correction factor for the effects of air temperature on photosynthetic rate It assumes that the leaf temperature LeafTemp C equals air temperature argument AirTemp and then follows equation 53 from Stockle s thesis PSTempFac 2 Tmax A LeafT emp A LeafT emp A Tmax A 1 where Tmax is the temperature for maximum photosynthesis here set to 25 C A is a constant which is adjusted to best fit the experimental response data in this model it is 5 C Private Function Growth_Stages This function is called at the end of each day and it returns the current growth stage which may change due to the accumulation of heat units First the day s effective degree days are computed as the daily mean temperature For wheat a base temperature of 0 C is used so that the numerical values of the daily mean and the degree days are the same The degree days are limited by a maximum temperature of 21 C in the early vegetative stages up to the third leaf s appearance and 35 C thereafter The degree days are accumulated into a running total that starts at zero when the crop is planted When the accumulated degree days exceed a variety specific threshold the crop enters a new growth stage These degree day thresholds may be set as varietal coefficients 1 13 in the plant input file if they are omitted the Init constructor of this crop model
39. The fraction of field capacity of each layer FFCjayer is computed as FFCjayer SES sim WN ayer soil DLL layer soil DUL layer soil DLLjayer where sim WN is the current volumetric water content and soil DLL and soil DUL are the lower and upper limits of available water as found in the soil input file Thus ifthe water content is at the upper limit FFC will be 1 if at the lower limit FFC will be 0 if there is freely draining water FFC will be greater than 1 From equation 2 we see that if FFC is 0 i e the soil is essentially dry the retention parameter s is equal to the parameter et which represents the maximum retention and thus the least runoff As FFC increases the retention parameter decreases and runoff increases Referring back to equation 2 we now discuss how the static parameters are derived To do this we first consider how the single curve number supplied as input CN is adjusted by a series of empirical equations for varying conditions CN2 is meant to represent average moisture conditions i e moist soil First a curve number for wet soil conditions CN3 is derived from CN2 by the following empirical equation CN3 CN3 e 0 00673 100 CN 4 At high curve numbers 1 e high risk of runoff the moist and wet curve numbers are essentially the same at low curve numbers the wet curve number diverges considerably from the moist curve e g at CN2 50 CN3 is 70 At saturated conditions the r
40. True if and only if the crop object is active 1 e if the simulation driver should call any plant processes at all The crop is assumed to be active between the planting and harvest dates specified in the plant input file GA PS Vorcinn 3 5 TTeor c Manual 45 Public Function is_transpiring This function returns True if and only if the crop object is transpiring i e actively growing in which case the simulation driver will call the crop s GetTransFrac function before partitioning potential evapotranspiration into evaporation and transpiration In the absence of more specific information this generic crop model assumes that the crop is transpiring during its entire lifetime 1 e between planting and harvest Public Function has_matured This function returns True if and only if the crop object is a grain crop which has matured i e grain filling has stopped but grain drying is proceeding in which case the generic crop model s Daily_Growth_End procedure will simulate grain drying In the absence of more specific information this generic crop model assumes that the crop is not a grain crop and so never matures therefore this function always returns False Private procedure grain_moisture This procedure is called by the generic crop model s Daily_Growth_End procedure at the end of each day for a mature grain crop i e one in which the grain is drying on the plant which is determined by a call to the active crop object
41. W m7 by multiplication with 11 574 1 86400 s dl 1000 SpaRad is irradiance above the atmosphere W m 2 SpaceSum is theoretical solar radiation for the day W m2 GA PS Vorcinn 3 5 TTeor c Manual an Next latent heat of evapotranspiration LE J m2 s lis calculated as LE SSVD sim NetRad G RO SVD VD RA PSYCON 1 RC RA SSVD 4 where RO is the specific heat capacity of air 1200 J m3 Kl RA is the canopy resistance to heat transport s mb PSYCON is the psychrometric constant 0 459 g m3 Kb RC is the canopy resistance to vapor transport s m7 and SSVD is the slope of the saturation vapor density curve g m3 Kb Latent heat of evapotranspiration is then converted into evapotranspiration sim ETP kg m2 s 1 by dividing by the latent heat of vaporization sim ETP LE LAMB 1000 5 where LAMB is the latent heat of vaporization 2430 J gl and multiplication by 1000 converts g into kg 5 3 3 Pan The procedure Pan_ETP uses daily measured values for pan evaporation provided in the climate input file clim PanEV and distributes the evaporative demand during the day using a sine wave function A pan coefficient loca Kp and a crop coefficient loca Kc can be specified in the location input file These are ratios of actual to measured evapotranspiration which are needed because water evaporates from the pan differently than from the soil surface or a crop Typical values of the pan coefficient
42. ae yl x f1 9 f9 a y2 x1 1x2 7 x1 Enter the two calibration points x153 fy 2 KE E Calculated S curve parameters a x f1 0 182 y 9 y2 x1 f1 x2 f7 y2 11309 a x7 f7 2 079 y 1 y1 x1 fp x2 f y1 3575 Graph of this function 1 0 05 1 1 0 8 sera Ge 0 4 0 2 0 FitSCurve procedure FitSCurve xl f1 x2 2 single var yl y2 single This procedure fits an S shaped curve of the form f x x exp yl y2 x from any two points on the curve x1 fl and x2 f2 It does this with the explicit solution y2 a x2 f2 a x1 fl x1 x2 yl a xl fl y2 x1 where a x f In x f 1 f GA PS Vorcinn 3 4 Tleor s Manual on SCurve function SCurve x yl y2 single single This function determines the functional value of an S shaped curve of the form f x x exp yl y2 x 5 5 2 Competition model none source file compete pas public procedures Init Done BeginDay TimeStep public functions MySolRad GetTransFrac GetPotTrans This is the base competition model and provides a skeleton for other competition models as well as default implementations of all public procedures and functions Constructor Init This constructor is called by the simulation driver as part of its initialization Init_Proc compete TheCompModel misclib Init Comp where procedure Init Comp then calls this constru
43. are 0 67 0 81 Shaw 1988 p 56 but these may vary widely by season even exceeding 1 Ideally the pan coefficient should be determined by long term studies at the site and the simulation should only be run for time periods with reasonably constant pan coefficients The crop coefficient loca Kc further corrects typically reduces the pan evaporation to account for a growing crop Ifa crop is being simulated this should be set to 1 as the crop model will adjust potential ETP to actual evaporation and transpiration This coefficient is useful when no crop is being simulated but it is assumed that there is a uniform crop cover at the site Again the value of crop coefficient should be determined experimentally Procedure Pan ETP Init uses the pan and crop coefficients to compute a time invariant coefficient PanCoeff 2 3 loca Kp loca Kc secs_in day 2 where secs_in_day is 86 400 s This coefficient is used as the amplitude of the sine wave at the time step resolution sim ETP PanCoeff clim PanEV real_day value 0 05 POW SIN 0 0175 7 5 ellapsed_hour 4 2 GA PS Vorcinn 3 5 TTeor c Manual Al 5 3 4 Linacre This module uses a simple empirical formula Linacre 1977 to estimate potential evapotranspiration from mean daily air temperature mean daily dew point temperature elevation and latitude If dew point temperature is unavailable minimum daily temperature is used as an approximation Thus th
44. assumption Within the GAPS simulation procedures there are two ways of considering the soil profile by layer and by node Layers are the soil as described in the input file and are used for calculations of volumetric water content Nodes are considered to be points in the middle of layers and are where the water potentials are measured The node depths are calculated from the layer boundaries in Int Sol source file misclib pas Defaults for all variables are set in procedure clear_soil source file fileio pas Each soil profile as a whole may have the following fields No Data field Variable name Units of Modules in which field is used measure Number of soil LastLayer count required for layer descriptions that layers less 1 follow Shortwave fraction Priestly_Taylor_ETP absorptivity of the Penman_ETP surface Default 0 78 3 Curve number CN2 index on Runoff CN 0 100 Water Uptake 0 10 EPIC_Water_Uptake see Distribution comments there Each layer of the soil may have the following fields GA PS Vorcinn 3 5 TTeor c Manual 14 No Data field Variable name Units of Modules in which field is used measure Lower boundary of LowBound m Soil_ Temperature soil layer Harmonic Soil Temp Tipping Bucket EPIC_Water_ Uptake Is Workable crop_model Daily Growth Begin NodeDepth WaterUptake derived from Harmonic Soil Temp LowBound LayThick m Soil_ Temperature derived from
45. at a given depth depth Proportion WUD depth l e rooting_depth WUD l e 1 Cumulative proportion as a function of depth for several values of the parameter WUD Proportion 0 5 depth Vo Proportion 1 depth 0 6 Proportion 2 depth 94 Proportion 5 depth This method accounts for multiple active crops in the same way as the Plant Available Water Uptake method see above The procedure works downwards from the top layer First the plant available water LayerAvail kg m2 in the layers in the soil from the surface to the last layer containing any roots i e MinRoot to sim LRoot is computed as the difference between the current water content sim WN m m3 and the wilting point soil DLL m m converted to a mass LayerAvailli sim WN 1 soil DLL 1 KgFines i 1 If the current water content is below the wilting point e g in near surface layers where evaporation has been effective this estimate may be negative in which case it is set to zero The following steps are performed for each active crop in order of their listing in the cropping sequence file not the order in which they were planted First the procedure obtains and stores the crop s potential transpiration from the competition model using an access method TheCrop crop_i PotTrans TheCompModel GetPotTrans crop_1 Next the potential water uptake in the current layer is c
46. called 5 5 3 Competition model modified ALMANAC The ALMANAC model was described by Kiniry et al as a general process oriented model for two competing plant species In its original form it is a modication of the EPIC crop model accounting for competition for light and water between a crop and a weedy competitior The GAPS competition model called ALMANAC follows the general structure of the original ALMANAC with several major differences e only the competition aspects of ALMANAC are included the atmospheric soil and plant water uptake processes modelled in ALMANAC i e their EPIC components have been removed and the various GAPS methods of modelling these may be selected by the GAPS user This allows the different crop models e g SORKAM Stockle Riha and Constant as well as EPIC to be used for the competing plant species e Competition for light follows the simpler and more tractable method of Wallace 1995 rather than the Spitters amp Aerts 1983 method used in the original ALMANAC e Corrections to radiation use efficiency due to vapor pressure deficit are not modelled actually these would be modelled in the EPIC crop model anyway since they don t depend on competition e The competition for plant water uptake modelled in ALMANAC is included in the appropriate water uptake methods Plant available a k a Simple and EPIC because the competitive uptake is a simple extension of these methods See
47. computed by summing the water contents in all layers in the case of ProfileAvail only the water above the lower limit is considered Despite the procedure name it also computes two summary variables related to heat both expressed in W 2 m NetHeatFlux accumulated net heat flux SumNetRad accumulated net solar radiation Finally if the model user requested a simulation of field hours and it is daytime and the soil is workable as determined by a call to the boolean function Is Workable the field hours for the day are incremented by the length of the time step 5 10 Soil temperature GAPS provides two ways to simulate the soil temperature by depth The first is based on a numerical solution to differential equations representing the heat fluxes in response to thermal conductivities very much analogous to the Richards Equation method of representing water flow The second is a simple harmonic wave by depth assuming that the soil is a uniform body with respect to thermal conductivity and water content If neither of these methods is selected the soil temperature remains at the initial value specified in the soil input file or if that is not specified the default of 20 C throughout the simulation 5 9 1 Heat flow equations source file soillib pas procedures Soil Temperature Init Soil Temperature Soil Temperature Don The change in soil temperature over time depends on the ability of the soil to cond
48. curve i e inverse exponential which passes through these points y In z depth_of evap e 1 1 1 where z is the independent variable depth from the surface y is the dependent variable 1 e the evaporation fraction on 0 1 and e is the Euler constant This has the effect of decreasing potential evaporation exponentially by depth This function can be simplified by combining the constants in 1 by setting R e 1 depth_of_ evap y In Rz 1 1 GA PS Vorcinn 3 5 TTeor c Manual Ina To integrate this e g over a layer we change variables x Rz 1 gt z x 1 R 2 leading to the definite integral Rz 2 Rx 1 1 ad 3 To determine the average fraction for a discrete layer we evaluate this definite integral over the layer and divide by the layer thickness We do this for layers from the surface downward until the evaporation fraction exceeds 1 i e evaporation is no more effective than drainage The actual computation of the evaporation fractions is now described The first step is to fit the curve through two depth fraction points 0 0 and loca depth_of_evap 1 by computing the scale parameter Ras R exp 1 1 loca depth_of evaporation 4 To initialize the by layer calculation we start the lower boundary of the previous layer which in this case is the surface and compute its contribution to the definite integral in 3 not including the scale divis
49. curve r r 0 1 0 1 variables only for Stockle Riha fast growing tree model 0 0142 plant_AccStemDM s kg m2 0 0193 plant _AccLeafDM s kg m2 0 024 plant SinkGrowRate s m d 3 plant_NSink i 10000 plant_LW_Sink i m kg 13000 plant LN Fine i m kg only for 0 18 plant SinkLength s m fast 4 358 plant_aWood s growing 2 90 plant_bWood s 1 tree 4 100 plant_aHeight s 1 949 plant_bHeight s 0 896 plant_cHeight s 25 plant _RefTemp i C 6 plant_SLA 1 m2 kg 365 Plant Init Age 1 a 1095 plant MaxLeafAge i a 0 02 OldRtBio 2 s kg m3 for n FRoot to NRoot 0 02 OldRtBio 3 s kg m3 0 015 OldRtBio 4 s kg m3 0 0017 OldRtBio 5 s kg m3 variables only for Sorkam crop model only for GAPS Vorcinn 2 5 Tleer s Manual 130 0 90 plant RowSpacing s m sorkam 9 plant_NLeaves i the following two ordered pairs are the x f at two points on the height vs degree days curve where x degree days AccUnitslto3 as a proportion of GDD_to_3 f corresponding proportion of MaxHeight 0 3 0 2 lst calibration point on height curve r r 0 1 0 1 Do 0 8 2nd calibration point on height curve r r 0 1 0 1 variables only for Epic crop model only for 0 31 plant _HarvestIndex s epic 0 0 plant _BaseTemp s degrees C 25 0 plant _OptimumTemp s degrees C 2000 0 plant PotUnits s
50. depth of plant _Sink Length m Drv Mater Accumulation roots Default 0 18 Grow_Sinkers Distribute Coefficient relating plant aWood Dry_Matter Accumulation stem diameter to Partition Form Aboveground wood biomass GA PS Vorcinn 3 5 TTeor c Manual 24 Coefficient relating plant bWood Default 2 9 stem diameter to wood biomass Coefficient relating plant_aHeight Default 4 1 diameter and biomass to height Coefficient relating plant_bHeight Default 1 949 diameter and biomass to height Coefficient relating plant_cHeight Default 0 895 diameter and biomass to height plant_RefTemp C Default 25 plant_SLA m2 kg Default 6 Reference temperature for maintenance respiration Specific leaf area Tree age at planting plant_Init_Age day Default 365 Maximum age for plant MaxLeafAge day aleaf 1 Row spacing plant_Row Spacing Default 1095 m Default 0 20 Dry_Matter_Accumulation Partition Form_Aboveground Dry_Matter_Accumulation Form_Aboveground Dry_Matter_Accumulation Form_Aboveground Dry_Matter_Accumulation Form_Aboveground Dry_Matter_Accumulation Maintain Dry_Matter_Accumulation Form_Aboveground Dry_Matter_Accumulation Form_Aboveground Dry_Matter_Accumulation Form_Aboveground constructor Initializes for dry_matter_accumulation Number of leaves Default 19 emergence Tropical DD EPIC crop model specific variables GA PS Vorcinn 3 5
51. equation used is ultimately based on that of Gardner 1960 q A k d WP d r 3 where q is water flux kg sh A is the cross sectional area for flow per unit length of root m kis hydraulic conductivity kg s m3 r is the radial distance for flow m and WP is soil water potential of soil or root J kg The cross sectional area for flow per unit length of root A is represented by A 2n plant RootRad 4 where plant RootRad is the radius of the root m This is a model input The unsaturated hydraulic conductivity sim K for each soil profile layer is calculated according to Campbell 1974 sim K soil HydCond soil AirEntryPot sim WP N 5 where soil HydCond is the saturated hydraulic conductivity kg s m3 soil AirEntryPot is the air entry potential J ke sim WP is the soil water potential J kg and N is computed as N 2 3 soil BValue 6 where soil BValue is the slope of the water release curve moisture content vs water potential when plotted on log log scale Substituting equations 4 and 5 into 3 gives q 2r plant RootRad soil HydCond soil AirEntryPot sim WP N dsim WP d r 7 GA PS Vorcinn 3 5 TTeor c Manual 117 Separating variables and integrating this equations results in q 2n In Res4 plant RootRad soil HydCond soil AirEntryPotN 1 1 N sim WP EN RootwP N 8 where Res4 is the distance from the center of the root to the point
52. file requires about 3 to 5 5 Kb on disk 3 4 1 5 Save file File suffix sav GAPS can periodically save its state to disk file for later printing plotting or input to other programs To get GAPS to do this the user must first specify the days and hours within the day to save and second specify the names of the output files to which to save the output using the menu option Scenario Output files a_file see following section on output files GA PS Vorcinn 3 5 TTeor c Manual 27 An output specification file requires about 1Kb on disk 3 4 1 6 Cropping sequence file File suffix seq This file is required if GAPS is to simulate more than one crop either in sequence relay cropping or at the same time intercropping or competition It lists the crops by their corresponding plant files plt and their starting and stopping year and day It also specifies the competition model and options See the Appendix for this file s format A cropping sequence file requires about 1 Kb on disk 3 4 2 Output files GAPS can periodically save its state to disk file for later printing plotting or input to other programs To get GAPS to do this the user must first specify the days and hours within the day to save and second specify the names of the output files to which to save the output using the menu option Scenario Output files a_file 3 4 2 1 Simulation log and summary file File suffix det
53. gravity 9 8 m s2 and U is a source sink term kg m3 sh In this discussion z is positive downward and WP is always negative This equations has to be solved numerically for realistic boundary conditions This model uses a network analysis approach to describe water transfer The soil profile is divided into a number of layers whose properties are assumed to be concentrated at the nodes The nodes are connected through conductors and associated with capacitors analogous to the electrical circuit problem Campbell 1985 The network problem can be solved numerically to determine the change in water potential and water content with time at each node Steady flow occurs within each element Storage is assumed to occur only at the nodes Mass balance equations are written for each node of the profile and solved for the unknowns using an iterative process the Newton Raphson method Campbell 1985 Similar schemes have been used by Stoeckle 1985 Weaver 1984 and Bristow 1983 to describe different aspects of the soil plant atmosphere continuum This model simulates infiltration redistribution and soil evaporation Input requirements for this procedure include soil physical parameters such as bulk density particle density saturated hydraulic conductivity air entry potential and soil b value slope of the moisture release curve Ifthese parameters have not been measured they can be estimated from soil textural data Campbell 1985 The
54. growth stage to pre emergence It also computes several parameters that do not vary during the course of the simulation including e the number of heat units needed to reach growth stage 3 GDD_to_3 this replaces SORKAM subroutine LEAF which keeps track of each leaf s development e for temperate cultivars the heat units needed to reach growth stages 2 and 4 e parameters X1 X2 and X3 used in SORKAM s empirical dry matter accumulation equation Destructor Done This procedure is called whenever an object of type SK_model is destroyed at run time Its only purpose is to deallocate the heap space used by the object Public procedure Daily_Growth_End This is called at the end of each simulated day First the daily mean temperature MeanTemp is calculated from the daily maximum and minimum air temperatures Next if the plant has not yet emerged the private procedure Emergence is called to simulate the seedling if the plant has matured no processes are simulated otherwise the plant is actively growing and following private procedures are called in order to simulate the growing plant e Soil Moisture Index determine today s composite soil moisture status GA PS Vorcinn 3 5 TTeor c Manual TA e Growth _ Stages determine if the growth stage has changed Dry Matter Accumulation determine how much dry matter is accumulated today eDaily Plant Growth partition dry matter and grow organs See the descriptions
55. i 2 If the current water content is below the wilting point e g in near surface layers where evaporation has been effective this estimate may be negative in which case it is set to zero The following steps are performed for each active crop in order of their listing in the cropping sequence file not the order in which they were planted GA PS Vorcinn 3 5 TTeor c Manual 110 First the procedure obtains and stores the crop s potential transpiration from the competition model using an access method TheCrop crop_i PotTrans TheCompModel GetPotTrans crop_1 Next we compute the proportion of the total profile root area in the current layer as r_frac LayThick layer TheCrop crop_i crop RootDens layer TheCrop crop_i TotalRoots 3 where RootDens is the root length density m m3 for this crop in this layer LayThick is the layer thickness m which converts this to a surface area and TotalRoots is the total profile root surface area m m 3 for this crop computed each day by 1 Assuming that uptake is proportional to root area we estimate the layer s uptake for this crop WUptake from its root area fraction and the rate of transpirational demand sim PotTrans kg m s as 2 WUptake r_frac TheCrop crop_i PotTrans AdditionalDemand time_step 4 where the mass AdditionalDemand kg m is unsatisfied demand from the overlying layers as now explained In the top soil layer
56. leaf m ground is the leaf area index of the growing crop and plant_ExtinctionCoeff is the extinction coefficient GA PS Vorcinn 3 5 TTeor c Manual AR 5 5 Competition GAPS V3 5 and later provide for multiple crops to be growing at once the limit is set by the constant global MaxCrops The competition module found in file compete pas has some non object procedures but is mainly made up of a hierarchy of objects and their methods similar to the organization of the crop models The TheCompModel variable is a pointer to any competition model and is always initialized to a non nil value Currently there are two competition models 1 comp_model associated with Comp_ option Comp_none No competition 2 AL model associated with Comp option Comp AL ALMANAC Some aspects of competition are found in other modules e plant water uptake with multiple crops were implemented as generalizations of the existing plant water uptake procedures SimpleWaterUptake and EPICWaterUptake 5 5 1 S curve procedures The competition module has two utility procedures associated with the S shaped growth curves that are used in several crop models source file compete pas public procedure FitSCurve public function SCurve Here is a MathCAD worksheet that may help visualize the S curve GA PS Vorcinn 3 5 TTeor c Manual 20 od x e Analytical solution for curve parameters x f 1 a x f m f y2 x1 f1 x9 f9
57. of each day to determine the current growth stage It also computes the daily heat units for base temperatures of 1 and 7 C DailyUnits and DailyUnits7 and the accumulated heat units in growth stages 1 3 and 4 AccUnits1t03 and AccUnits4 which are used in the daily plant growth procedure as well as in this function First we check if the plant has been killed by frost This happens if the growing point is vulnerable i e in growth stages 2 through 5 and the daily minimum temperature is below 2 2 C Note that until growing point differentiation the growing point is protected below the soil surface Next the daily heat units for base temperatures of 1 and 7 C DailyUnits1 and DailyUnits7 are determined by calls to theheat units function The base 7 C heat units are then adjusted for the effects of water stress SORKAM eqns 58 and 59 Before anthesis they are multiplied by the water stress coefficient WATCO thereby reducing the effective heat units i e potential growth with water stress After anthesis water stress hastens physiological maturity which is accomplished in the model by increasing the effective heat units if the soil moisture index SMI is less than 30 DailyUnits7 DailyUnits7 1 1 SMI 0 67 1 Note that a smaller SMI representing less soil water results in an increase in heat units GA PS Vorcinn 3 5 TTeor c Manual 70 The daily heat units are then accumulated into the cumulative hea
58. of the layer m3 m3 soil AirEntryPot is the air entry potential at the node J ke sim WP is the water potential at the node J ke and soil BValue is the slope of the water release curve of the layer moisture content vs water potential when plotted on log log scale GAPS Vorcinn 3 5 TTeor c Manual INT 5 5 1 6 Sub procedure Calculate_Fluxes Once the solution to the Richards Equation satisfies mass balance criteria this procedure is called to calculate the changes in amount of water for each layer and the whole profile Fluxes between layers are also calculated and new water contents which will be used as initial conditions at the next time step are determined The water content change for each layer in the profile is calculated Node WC Chef KgFines I sim WN I WOD 1 where KgFines I kg m3 converts from volume to mass in a layer sim WN is the updated water content just computed during the last iteration of the Richards Equation solution m3 m3 and W is the water content at the beginning of the time step m3 m3 The changes for each layer are summed up to get the change in amount of water for the whole profile and the rate of change WC_Change kg m2 sh 1s calculated by dividing the total flux by the time step The fluxes for each node are calculated from the final values of the water potentials at the node and the one below it sim WFlux I sim K sim WP I sim K I 1
59. of the moisture index to the threshold SORKAM eqn 53 water_stress SMI AdjustedThreshold 2 GA PS Vorcinn 3 5 TTeor c Manual 78 Private Procedure soil_moisture_index This procedure computes the current soil moisture status as the index SMI on 0 1 very dry to saturated and with this calls the water_stress function to determine the current water stress coefficient WATCO on 0 1 extreme to no stress The soil moisture index is calculated from the weighted ratio of the current volumetric water contents sim WN to the drained upper limits field capacity soil DUL of the layers in the current rooting zone sim LRoot soil WN ayer KgFinesayer layer plant FRoot SMI 1 sim LRoot soil DULjayer KgF ines ayer layer plant FRoot where KgFines is the mass of the fine earth fraction in the layer which weights the moisture contents appropriately Private Function Growth_Stages SORKAM models the phenological development of the sorghum plant in seven growth stages pre emergence emergence to growing point differentiation growing point differentiation to the end of leaf growth end of leaf growth to anthesis anthesis to physiological maturity post physiological maturity dead i e frozen or harvested DU uno The crop progresses from one growth stage to another according to accumulated heat units possibly modified by water stress This function is called at the end
60. of the simulation drtver cece cece eeceeeeceeeeeeeaeeeeeeeeeeceeeseeeaeeeseesaeeeeeeaes 33 3 1 1 DepthAndHeisht a Eege rege Sie Zeep 36 52s Atmospheric Processes cron u oases a a 36 5 2 1 Function Air temperature ENEE a ENEE ENNEN NEEN BE 36 5 2 2 Computation of solar angles 36 5 2 3 Distribution of precipitation over the day 37 5 3 Vapor exchange evapotranspniraton 38 5 3 1 Priestley Taylor oc 2 seen a ei kin ABER 38 3 3 2 PENDA EE 39 MA EN ee seth ves ia Beeren 41 A DN E te 42 3 44 Plant processes a ee alas 44 SAL Crop Mod a adga ibas 44 5 4 2 Crop model Stockle Riha 0 ccc ccecceecceecceecceeeeeeeeeeeueeceeeseeeaeeeaeeeeenaes 46 5 4 2 1 Crop model Stockle Riha matze 53 5 4 2 2 Crop model Stockle Riha wbeat 60 5 4 2 3 Crop model Stockle Riha Fast Growing Tree 68 5 4 3 Crop model modified SORKANM essen 75 5 4 4 Crop model CONSTAN Troel nennen 84 5 4 5 Crop model EPIC model nieni i i i E a E E E 85 KREE Ree an ri Kirn hl ii Rep E set ines tapuia ui 89 5 5 1 S curve procedures nenn again en nase id 89 5 5 2 Competition model none 91 5 5 3 Competition model modified ALMANAC nenn 93 9 0 8011 Water flOw Processes sack oh Sak eier ae O EE 95 5 921 Rich rds equation a eege here reger 96 3 9 2 Tipping bucket u A Im drin 102 3 9 3 Matric flux potential ae ise nee Bebe 109 5 5 4 Workability and Traffiteabultv 110 Se 7 RUNGE tt dev EEE 113 5 6 1
61. preferentially distributed in the wetter regions of the soil profile New stem and leaf biomass are added to their respective plant parts here and the sum of root biomass is recalculated GA PS Vorcinn 3 5 TTeor c Manual 74 Private Procedure Form_Aboveground Form Aboveground computes a new tree height and takes care of bookkeeping on leaf ages and senescence Tree height is calculated using the allometric relationships defined by the parameters input by the user in the plant file In_diam In TreeWood aWood bWood In_height In TreeWood aHeight bHeight In_diam cHeight crop CanopyHeight EXP In_height Leaf cohorts are represented in two arrays one defining leaf biomass for each cohort Leaf Cohort i and the other for the age in days of each leaf cohort Cohort_Age j At any point in time some number of cohorts exists each having an age and a quantity of biomass Every 30 days a new cohort is formed and becomes the recipient of all new leaf biomass Cohort age is incremented as a function of both days passed and water stress as follows Cohort_Age i Cohort_Age i 1 WaterStressFact Once a cohort reaches the user defined maximum leaf age it is senesced from the canopy and the biomass is subtracted from the total leaf biomass If the cohort did not experience any water stress during it s lifetime it would remain on the tree for the number of days equal to Max_Leaf Age But stress speeds the aging
62. process causing leaves to fall more quickly which decreases the transpiring surface and thus the demand for water Under a period of prolonged drought leaf area may decrease substantially as has been observed in the field Pook 1985 3 The final calculation is of the leaf area density LAD m leaf area m canopy volume which is not constant throughout the life of the tree If Tree_Age lt 1095 days then LAD 0 0137 Tree_Age 15 else LAD 1 This defines LAD as decreasing from 10 m m at planting to about 1 m2 m at three years The LAD is used in procedure Light _ Interception to calculate canopy volume 5 4 3 Crop model modified SORKAM source file sorkam pas object name SK model public procedures Daily Growth End End Growth TimeStep Growth open det file write summary public functions GetTransFrac is active is transpiring has matured private procedures soil moisture index emergence dry matter accumulation daily plant growth private functions heat units water stress growth stages This model is a modification of the SORKAM grain sorghum crop growth model of Rosenthal et al 1989 The main differences from the original SORKAM are GA PS Vorcinn 3 5 TTeor c Manual 75 e only the plant processes of SORKAM are included the atmospheric soil and plant water uptake processes modelled in SORKAM have been removed and the various GAPS methods of modelling these
63. root water potential is not allowed to drop below this value WaterUptake WaterUptake 2 These fields are ignored if there is a cropping sequence seq file for the simulation run In this case the dates in the sequence file are used instead The dates in the plant file are retained for backwards compatibility in single plant simulations that do not need a cropping sequence file GA PS Vorcinn 3 5 TTeor c Manual 10 First shallowest soil layer that can contain roots Last deepest soil layer for which RootDens field 11 is specified RootDens FRoot NRoot Root length density for each layer from FRoot to NRoot Maximum height of canopy Aerodynamic resistance Resistance of canopy when stomates open Shortwave absorptivity of plant canopy GA PS Vorcinn 3 5 TTeor c Manual soil layer number 2 MaxLayer Default 2 soil layer number 2 MaxLayer Default MaxLayer 1 m of root length m3 soil volume Default 5 0 x 104 m Default 1 5 s m Default 30 0 s m Default 20 0 dimension less Default 0 75 nN SimpleWaterUptake WaterUptake SK_ model Soil_Moisture_Index crop_model Daily Growth Begin crop_model Daily Growth Begin Limited at run time to the last layer in the soil profile SimpleWaterUptake WaterUptake Penman_ETP SR_model SE_model SK_model SC_model Note gt 0 01 Penman ETP only used if daily clim Wi
64. selection of a valid scenario file the input and output files the model procedures the selected graphs and the time specifications will be set according to those described in the scenario file Save scenario pops up the Save scenario dialog box Type a scenario filename or select an existing file The current settings will be saved in that scenario file Input files pops up the Select dialog box for the selection of the climate location soil plant file 1 plant file 2 and save input files If Escape or Cancel is selected the previous selection is cleared out Output files pops up the Select dialog box for the selection of the Soil layer Soil flux Plant flux Climate flux Daily summary and Model summary output files If Escape or Cancel is selected the previous selection is cleared out Model procedures pops up the Model procedures dialog box for selection of the ETP Flow Water Uptake and Temperature procedures the Field hours and input models Time the simulation time dialog lets you enter the time step in seconds the first and last day of the simulation and the numbers of years to simulate maximum 11 By default the first and last day of simulation are set to the first and last day specified in the scenario file Runtime Graphs Select Graphs the first 4 selected graphs will be displayed at runtime Use the Tab and or arrow keys to move to another selection Settings lets you change the scale of th
65. sim ActEva ktw 8 AirTemp ktw 2 453 000 GAPS Vorcinn 3 5 TTeor c Manual 161
66. status line If you have a mouse installed simply click on the desired menu and submenu options You can also drag straight from the menu option to the submenu option When a particular option doesn t make sense in the current context it will be disabled and appear dim GA PS Vorcinn 3 5 TTeor c Manual A 3 2 2 The status line The status line appears at the bottom of the screen Besides reminding you of some of the most important hot keys it offers one line descriptions about the selected menu option You can click on the hotkeys on the status line to carry out the action instead of selecting the command from the menu or pressing the hot key Example To quit GAPS you can either Press F10 select the File option using the arrow keys the Enter key or by pressing Alt F or F and select Exit using the arrow or End keys the Enter key or by pressing Alt X or X Click on the File option in the menu bar and then click on the Exit option in the submenu Click on the File option in the menu bar drag straight down to the Exit option and release the mouse button Press the hot key Alt X Click on Alt X Quit on the status line 3 2 3 The desktop Except for the runtime and postrun graphs all you see and do happens in a window or dialog box Windows The editing of the input and output files occurs within windows The windows are opened on selection of a file for editing or on creation of a new input file A win
67. than 13 6 hours This assumes that the daylength is increasing at emergence If the daylength is shorter these are set to the constants 370 and 1020 respectively SORKAM eqns 5 and 8 The daylength is determined as twice the difference from noon to sunrise which in turn is determined from the solar declination on the emergence day and the latitude For tropical cultivars the actual number of leaves that will appear is adjusted for the heat units needed to reach anthesis following SORKAM equation 9 NLeaves trunc GDD_to_4 5 71 64 29 4 Private Procedure dry_matter_accumulation This procedure based on SORKAM procedure PHOTO is called at the end of each day from emergence to physiological maturity to determine the amount of dry matter produced by the plant during the day Unlike the Stockle Riha models the SORKAM model does not explicitly model photosynthesis but instead estimates the photosynthetically active radiation PAR intercepted by the plant from the mean air temperature This is then converted to dry matter by an empirical formula which takes into account the daily water stress First the proportion of the PAR that is transmitted i e not intercepted by the leaves PctTrans is estimated from the leaf area index LAI and several empirical parameters that related LAI and row spacing In growth stages and 2 PctTrans 100 exp 0 7675 LAT if LAI lt X3 la PctTrans X1 exp X2 LAD if LAI gt
68. the current layer GA PS Vorcinn 3 5 TTeor c Manual 72 Private Procedure Partition A variation on the theory of functional equilibrium Brouwer 1962 Davidson 1969a b Wilson 1988 was utilized in developing the procedure for partitioning biomass to new roots stem and leaves The essential feature of the theory is that above and below ground plant parts both supply and consume products necessary to sustain life and therefore must maintain some functional balance between their relative sizes In this case we are concerned with the supply and demand for photosynthate and water It is assumed here that the tree will maximize the amount of biomass it partitions to leaves within the constraints created by limitations on water uptake As long as there is no water stress the tree can continue to expand its leaf area and thereby increase the demand for water Ifthe demand exceeds the supply of water by the roots photosynthate will be partitioned to roots until the stress is relieved Because the ability to take up water per unit root biomass will vary with soil water content and location in the profile a means of integrating the limitation to soil water uptake over the day was necessary As an approximation of the effective demand for root biomass the ratio of potential to actual transpiration for that day is multiplied by the quantity of existing new root biomass summed over all layers SumNew A maximum limit of double the roots and if
69. the tree is still young a minimum of 1 115 times the root biomass were set if ActTrans lt 0 5 SumPotTrans then ActTrans 0 5 SumPotTrans if SumPotTrans ActTrans lt 1 11 and Tree_Age lt 400 then Pot Root SumNew 1 11 Pot_Root SumPotTrans SumActTrans SumNew RT_demand Pot_Root SumNew Pot_Root is the amount of root biomass that would have been required to meet the potential demand for water given today s moisture and biomass distribution in the profile The added constraint of a minimum potential root biomass reflects the limitations of the functional equilibrium model to provide a full explanation of partitioning above and below ground plant parts The difference between existing roots and potential roots then equals the root demand for this day Distribution within the profile is computed in the sub routine Distribute Roots A slightly different approach is taken in the calculation of the demand for stem biomass While root demand is estimated as a function of the ratio of potential to actual transpiration and is therefore directly related to the demand for water stem biomass is indirectly related to the demand for water through an assumed relationship with leaf area In accordance with the Pipe Model theory Shinozaki et al 1964 for each increment of new leaf area a corresponding area of xylem must be added to conduct water to it Thus a relationship between new leaf area and new stem cross sectional area may
70. these methods for details ALMANAC does not account for the actual horizontal and vertical geometry of plants in the field instead the LAI and height are used to model spherical light interception GA PS Vorcinn 3 5 TTeor c Manual 02 This model object is descended from the generic competition model type AL_model object comp_ model It only over rides the BeginDay procedure It also is required to have a constructor and destructor Public procedure BeginDay This procedure is called by the simulation driver at the beginning of each day when there are any active crop models after solar angles are computed but before any crop events including planting and harvesting Its first purpose is to partition the day s solar radiation among the active crop models To do this it first collects information from each active crop 1 the crop s transpiration fraction and 2 the crop s canopy height The transpiration fraction must be supplied by an access procedure in each crop model if TheCrop crop_i lt gt nil then TF crop_i 1 TheCrop crop_1 GetTransFrac where TheCrop crop_i is a pointer to crop model crop_i and TF is the complement of the transpiration fraction i e it is the proportion of light that is not intercepted by the crop in monoculture The model keeps a running sum of exponentials product of fractions for total interception IntFact IntFact TF crop_1 where IntFact was initialized to unity
71. water contents and unsaturated hydraulic conductivities by depth over time It requires as input parameters the soil moisture release curve matric potential vs volumetric water content the saturated hydraulic conductivity and the air entry potential of each layer These parameters are usually obtained through detailed physical measurements This is an appropriate model ifthe modeller has these physical data and needs to know the fluxes and potentials by depth If plant water uptake is being simulated as being controlled by leaf and root water potentials e g Critical_leaf water potential and WaterUptake procedures the Richards equation must be used The Matric flux potential method is a variant of the Richards equation method and has identical parameter requirements and output 5 5 1 Richards equation The soil water balance is obtained by a numerical solution of the Richards equation which describes water flow and storage in soil This equation is obtained by applying the continuity equation to Darcy s law Campbell 1985 w CP dWP dt d dz K WP dWP dz K WP GR U 1 where w is the density of water kg m3 CP is the specific water capacity CP de dWP 6 is the volumetric soil water content m3 m3 WP is the soil water potential J kg t is time s z is depth m K WP is the soil hydraulic conductivity kg s m3 which is a function of the water potential GR is the acceleration of
72. water potentials sim WP J kg l of this layer and the one above upstream from it the current hydraulic conductivity K kg s m3 above the node and a moisture release parameter N using the relation sim WFlux I K I 1 sim WP I 1 KI sim WP I NodeDelta I 1 1 NI 1 where N I is related to the slope of the moisture release curve BValue I by N I 2 3 soil BValue I 2 after Campbell 1974 and NodeDelta I is the distance m from of soil node to the node below it This is computed before simulation starts in procedure InitSoil in source file misclib pas from the soil input data as NodeDelta I NodeDepth I 1 NodeDepth I 3 where NodeDepth I is computed as the midpoint of soil layer Z NodeDepth I soil LowBound I 1 LayThick T 2 4 where soil LowBound I 1 is the upper boundary of layer J and LayThick 1 is the thickness of layer J computed as LayThick I soil LowBound I soil LowBound I 1 5 Combining this equation with the mass balance equation for layer Z GA PS Vorcinn 3 5 TTeor c Manual OR FGauss I WFlux I 1 WFlux I UA 1 UM KgFines I WN I W I time_step 6 where KgFines I kg m3 converts from volume to mass in a layer and letting the source term U I GR K I i e the flux into the node is the hydraulic conductivity times the driving force of gravity GR m Ben yields the mass balance e
73. where sim WP is measured which is calculated according to Gardner 1960 by Res4 n plant RootDens 0 5 9 where plant RootDens is the length of root per unit volume of soil m m3 The resistance form of equation 8 is q plant RootDens sim WP RootWP Res 8 where the combined resistance Res is Res4 plant RootRad 2x plant RootDens soil HydCond soil AirEntryPotential 1 N In Res im WP RootWP nn plant RootRes 10 sim WP N RootwP N Substituting eq 9 into eq 10 gives 1 HA er 1 N In nora Va RootDens sim WP RootWP Res 11 2n RootDens HydCond AirEntryPotential sim WP RootwP 3 The calculation of Res is straightforward for the soil resistance component of equation 11 when RootDens RootRad B sim WP HydCond and AirEntryPotential are specified with depth In subprocedure Resistances the calculation of Res through Res4 solves the soil resistance component of eq 11 as a function of depth Root resistance with depth knowing the total root resistance Res kg s m4 is calculated as follows Campbell 1986 RootRes I RootRes RootDens I LayThick I 12 where LayThick I is the vertical thickness of the layer m 5 7 1 2 RootWaterUptake Knowing the root water potential RES I and sim WP I the root water uptake in each layer sim WUptake kg m2 sl is calculated from the equation GA PS Vorcinn 3 5
74. will use the following defaults for a standard wheat variety Heading completed 960 ____________ In addition at the end of heading the initial number of grains set GrainNumber is determined by a call to the Grain_Number private function Private function Grain_Number This function is called at the end of flowering to compute the initial grain set from the accumulated dry matter and the record of water stress accumulated in earlier growth stages It first computes the potential number of grains PotGrainNumber grains m2 as GA PS Vorcinn 3 5 TTeor c Manual A PotGrainNumber PotEarsInRow plant RowSpacing 100 PotGrainsPerEar 1 where the ears in row and grains per ear are constant parameters Then multiplicative factors on 0 1 to account for the effects of cumulative water stress during the early vegetative stages STFactor the late vegetative states SJBHFactor and heading SHFactor are determined by empirical relations All three of these then multiply the potential grain number to arrive at the actual number which is the function result Grain_Number PotGrainNumber STFactor SJBHFactor SFFactor Q Private procedure Dry_Matter_Accumulation This procedure is called at the end of each day from emergence until flowering is complete to compute the amount of new dry matter from the amount of photosynthate accumulated during the day and the current carbon reserve CRes kg m2 which is adju
75. 0 BLC 0 RainFirst 24 RainLast 0 0 WindHeight 305 Elevation 0 150 WorkMaxDepth n 0 050 WorkMaxDepth n 0 370 WorkLimitWN n 0 370 WorkLimitWN n 9 8 WorkLimitWP n 9 8 WorkLimitWP n 0 050 Depth_of evap 0 54 CO2Ext GA PS Vorcinn 3 5 TTeor c Manual Comments added after the input data The climate file must be saved with the extension s70 string 70 s70 s s s s s s 1 1 s s s s s s s s s s 14 LOC sign are ignored at input preceded by a are also ignored N or S s Priestly Taylor coefficient 0 1 Pan coefficient 0 1 crop coefficient W m2 K h h m m m till m m3 m3 m3 m3 J kg J kg m g m3 for n 1 to traffic 2 for n till 1 to traffic 2 for n till 1 to traffic 2 3 _ Soil file example sol GAPS 3 0 soil file The soil file must be saved with the extension SOL Lines starting with the sign are ignored at input Comments added after the input data preceded by a are also ignored i integer s single s70 string 70 Dickman SL 0 2 SoilName s70 00 SwAbs s 0 1 00 78 CN2 i 0 100 0 00 Slope s 2 WUD s 0 10 2 Layer i LastLayer Minimum of Layer and MaxLayer 1 1 layer inputline for n FirstLayer to LastLayer alle 8 LowBound s m BulkDensity s Mg m
76. 000 0 000 0 074 0 074 0 002 0 081 0 081 0 000 150 C gt ESPOSAS E E O E E ESA ESO EA CO OO OO OO OO OO OO OO OO OO OCH 35229999 9 I O Root Biomass kg m3 000 000 20010330 000 ODO DTO 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 10 WaterP mm3 245 243 242 248 240 240 240 244 240 241 240 242 240 241 239 238 2 160 12 0 708 0 608 0 016 0 100 0 100 0 000 0 016 0 100 230 170 12 1 410 0 958 0 000 0 451 0 451 0 000 0 000 0 451 213 180 12 0 587 0 218 0 000 0 369 0 369 0 000 0 000 0 369 182 190 2 0 747 0 078 0 078 0 669 0 669 0 000 0 000 0 747 187 200 12 0 610 0 032 0 032 0 579 0 421 0 000 0 000 0 452 221 210 12 0 472 0 021 0 021 0 450 0 327 0 000 0 000 0 349 178 220 2 0 05 33 0 022 0 022 0 511 0 511 0 000 0 000 0 533 156 230 12 0 761 0 039 0 039 0 722 0 363 0 000 0 000 0 402 171 240 12 0 472 0 037 0 037 0 434 0 218 0 000 0 000 0 256 175 Note that all water flux densities are in units of kg m2 s in the SOF file 1 2 3 4 5 6 7 8 9 10 11 1 day 7 sim ActTrans 3600 2 hour 8 Drain_rate 3600 3 sim ETP 3600 9 WIn 3600 4 sim PotEva 3600 10 WC_change 3600 5 sim ActEv 3600 11 ProfileWater 6 sim PotTrans 3600 12 ProfileAvail Plant flux plantfl txt PLF Data File Name C GAPS3 EXAMPLE PLF Date 5 24 1994 Time 10 43 58 Day Hour PotTrans ActTrans RootWP LeafWP PS NonStressRes PSStressFac
77. 000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 0 07 50 0 050 0 324 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 0 08 50 0 050 0 324 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 0 09 50 0 050 0 324 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 H 10 50 0 050 0 324 17 17 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 0 0E 0000 20 0 20 0 Or 1 lt 2 gt lt 3 gt lt 4 gt lt 5 PS 6 gt lt R SE 1 decimal day 6 sim WUptake MinLayer to LastLayer 2 sim WN MinLayer to LastLayer 7 sim SoilTemp MinLayer to LastLayer 3 sim WP MinLayer to LastLayer 8 sim AccLayerRtBio MinLayer to LastLayer 4 sim K MinLayer to LastLayer 5 sim WFlux MinLayer to LastLayer Soil flux example sof 1 50 0 0000344 0 0000344 0 0000344 0 0000000 0 0000000 0 0000000 0 0000000 0 0000344 245 SH 10 50 0 0000545 0 0000545 0 0000545 0 0000000 0 0000000 0 0000000 0 0000000 0 0000545 243 30 20 50 0 0000434 0 0000434 0 0000434 0 0000000 0 0000000 0 0000000 0 0000000 0 0000434 242 28 30 50 0 0000409 0 0000409 0 0000409 0 0000000 0 0000000 0 0000434 0 0000000 0 0000844 248 34 40 50 0 0000571 0 0000571 0 0000000 0 0000000 0 0000000 0 0000000 0 0000000 0 0000000 240 26 50 50 0 0000773 0 0000773 0 0000000 0 0000000 0 0000000 0 0000000 0 0000000 0 0000000 240 26 60 50 0 0000563 0 0000563 0 0000000 0 0000000 0 0000000 0 0000000 0 0000000 0 0000000 240 26 70 50 0 000105
78. 00545 0000434 0000409 0000000 0000000 0000000 0001052 0000000 0001029 0000301 0000783 0000000 0002115 0000000 0000000 0000046 0000000 0000000 0000217 0000089 0000060 0000061 0000109 0000104 3 0 0 10 0 0 0 0 0 0 0 60 0 0 0 0 0 0 0 0 0 0 0 0 0 GA PS Vorcinn 3 5 TTeor c Manual 0000000 0000000 0000000 0000000 0000000 0000000 0000000 0000000 0000000 0000000 0000000 0000000 0000000 0000000 0000207 0000227 0000278 0001255 0001027 0001860 0001170 0000910 0001421 0001010 0000607 4 00 7 00 1 00 9 00 Sh 00 3 HOD t 2 5 00 7 00 10 00 10 OOO 0 00 OOOO O OFS O O Ov Or OO OOO EE O KE 157 28 00 15 00 28 00 21 00 21 00 32 00 18 00 24 00 24 00 25 00 26 00 22 00 27 UONDNONSOOOPHNANDNOUOPOO ON HM OMN GA D 230 280 314 2125 314 420 385 399 595 636 569 294 940 669 802 AL 395 9553 489 556 455 350 389 391 339 RU Vo ou JARONOO is as 0130101010 GA k OO k Printout of output files Model summary id example det Daily summary daily txt SUM Data File Name Date Time Day ETP PotEV AcEV SU RUN m SR IS SA Sa ar EE EM a a Ge E A E 2000000000 O0 ON NONOOOOoOrROo Duo DS bee jes oe eS N LA A day sim POTET sumPotEV sumev sumPotTrans sumActTrans Soil layer layer txt LAY Data File Na
79. 1 This equation is rearranged to solve for RESxxx and also divided by 1 65 to convert from CO to water vapor resistance Campbell 1977 ResSun COext COint PSSun RaCO 1 65 12 ResShade COext COint PSShade RaCO 1 65 13 To obtain the whole canopy non stress resistance to water vapor transfer the sun and shade lit resistances are weighted according to the proportion of sun and shade lit leaf area and added in parallel Stockle and Campbell 1985 NonStressRes LAI LAISun ResSun LAIShade ResShade 14 This is an optimization approach to predicting water vapor loss from a plant canopy since there is an implicit assumption that the plant only opens its stomates the amount necessary to achieve maximum photosynthesis and is never losing more water than required to achieve this rate Private procedure Limit_Photosynthesis This procedure is called every hour to limit the photosynthetic rate PS g m sh calculated in procedure Max Photosynthesis according to the stress factor PSStressFact calcaulated in procedure Critical Leaf Water Potential if the Critical Leaf Water Potential simulation option was selected by the model user or Simple Water Stress otherwise as follows PS PS PSStressFact GA PS Vorcinn 3 5 TTeor c Manual 57 This procedure also accumulates a factor LAIStressFact which is used in daily procedure Dry Matter Accumulation to accelerate the decline in leaf a
80. 1 Then if the depth is greater than another user input in the plant file namely plant MaxRootingDepth it is limited to that depth This would be appropriate if the user had field observations of a maximum or wanted to artificially limit rooting depth to certain horizons to simulated water stress 5 4 2 1 Crop model Stockle Riha maize source file stockle pas object name SRm_model public procedures Daily Growth End End Growth open det file check model PSTempFac public functions GetTransFrac PSTempFac is active is transpiring has matured private procedures Limit Photosynthesis Max Photosynthesis Dry Matter Accumulation Yield GetTransFrac private functions Growth Stages This submodel implements specific procedures for modelling the maize crop GA PS Vorcinn 3 5 TTeor c Manual 52 There are several differences between the original model and its implementation in GAPS which are summarized in the following table Current Implementation Stockle amp Campbell 1985 Water Stress Correction on not included partitioning of dry matter Root resistances as a function of not included time Root Density as function ofroot not included dry matter and thermal time Critical leaf water Critical eat water potential Critical eaf water potential 400 J 1 1800 J sos Conversion factor photosynthesis 0 40 2 0 46 0 50 3 0 31 0 34 4 to dry matter Expone
81. 150 iz 0 918 4 5 K kg s m3 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 CO OO OO OO OO OO OO OO OO OO OCH WFlux 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 WUptake kg m2 hr III IST 0 O9 2 2 DD 0E 0000 0E 0000 0E 0000 0E 0000 0E 0000 E 0000 E 0000 E 0000 E 0000 E 0000 E 0000 E 0000 E 0000 E 0000 E 0000 E 0000 E 0000 E 0000 E 0000 SA 9925095995 Oo DD 25 0E 0000 SoilTemp in units of kg m2 s in the LAY file 6 SOC AND sim K layer sim WFlux layer 3600 7 8 sim WUptake layer 3600 sim SoilTemp layer sim AccLayerRtBio layer C GAPS3 EXAMPLE SOF 5 24 1994 10 43 25 IT IF IT II DIT IDEE 836 GA PS Vorcinn 3 5 TTeor c Manual ActEv 123 196 156 147 000 000 000 378 000 370 108 281 000 7 01 000 000 00000000000 OO OO OO OO CH PotTrans ActTrans Drain kg m2 hr 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 156 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 002 0 000 0 000 0 000 0 000 0 000 0 121 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0 000 0
82. 2 0 0001052 0 0001052 0 0000000 0 0000000 0 0000008 0 0000212 0 0000849 244 30 80 50 0 0001621 0 0001621 0 0000000 0 0000000 0 0000000 0 0000000 0 0000000 0 0000000 240 26 90 50 0 0001797 0 0001797 0 0001029 0 0000000 0 0000000 0 0000338 0 0000000 0 0001366 241 27 100 50 0 0001593 0 0001593 0 0000301 0 0000000 0 0000000 0 0000000 0 0000301 0 0000000 240 26 110 50 0 0000783 0 0000783 0 0000783 0 0000000 0 0000000 0 0000000 0 0000792 0 0000009 242 28 GAPS Vorcinn 2 5 Tleer s Manual ee 120 130 140 150 160 170 180 190 200 210 220 230 240 Dd Us Um hi 50 0 0003694 50 0 0002115 50 0 0003149 50 0 0002550 50 0 0001969 50 0 0003917 50 0 0001633 50 0 0002077 50 0 0001697 50 0 0001311 50 0 0001482 50 0 0002116 50 0 0001311 1 2 decimal_day sim ETP sim PotEva sim ActEva sim PotTrans sim ActTrans 2292229229999 0003694 0002115 0002942 0002323 0001691 0002662 0000607 0000217 0000089 0000060 0000061 0000109 0000104 3 Plant flux example plf Gs Ghia 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000000 50 0 0000207 50 0 0000227 50 0 0000278 50 0 0001255 50 0 0001027 50 0 0001860 50 0 0001609 50 00001251 50 0 0001421 50 0 0002007 50 0 0001207 1 2 decimal_day sim PotTrans sim ActTrans sim RootWP leafWP oo
83. 240 26 0 00 177 89 0 010 0 010 66 4 66 2 18 0 00 0 00 3 36 5 55 0 00 240 27 0 00 195 00 0 010 0 010 38 4 38 1 87 0 00 0 00 0 00 0 62 2 49 240 26 0 00 186 65 0 010 0 010 30 2 30 2 30 0 00 0 00 0 00 4 25 6 55 244 30 0 00 102 20 0 010 0 010 96 10 96 0 00 0 00 0 00 0 00 0 00 0 00 240 126 0 00 329 74 0 010 0 010 35 6 35 5 96 0 00 0 00 0 00 0 82 5 14 241 27 0 00 237 72 0 010 0 010 70 9 06 0 00 0 64 0 64 0 10 0 74 0 00 238 25 0 00 291 89 0 013 0 012 97 7 26 0 00 0 71 0 71 0 00 0 71 0 00 237 124 0 00 268 66 0 019 0 016 46 5 55 0 32 0 91 0 91 0 00 0 84 0 38 230 17 0 00 214 91 0 034 0 026 62 8 58 0 00 4 04 4 04 0 00 4 04 0 00 211 98 0 00 363 09 0 092 0 072 16 1 92 0 00 3 24 3 24 0 00 3 24 0 00 181 68 0 00 181 52 0 217 0 175 co en CO COOC OO OO OO OO OO OO CH 000 000 000 000 000 000 000 000 000 000 000 000 000 000 001 003 007 020 042 CO e COOC OO OO OO OO OO OO CH 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 190 6 37 0 67 0 67 5 70 5 70 0 00 6 37 0 00 184 71 0 00 202 43 0 521 0 436 0 085 0 000 200 5 28 0 28 0 28 5 01 3 64 0 00 3 92 0 00 219 105 0 00 167 72 0 864 0 739 0 124 0 000 21 0 4 20 019 019 4 01 2 29 0 00 8 11 0 00 176 63 0 00 132 431 353 L 180 00 173 0 000 220 4 09 0 19 0 19 24 36 4 236 01 00 4 55 0 00 154 40 0 00 140 00 1 781 1 570 0 210 0 000 230 6 05 0434 0 31 5 74 208 9 0 00
84. 25 0 plant BiomassEnergy s kg M3 0 60 plant DeclineFraction s 4 0 plant MaxPotLAl s the following two ordered pairs are the x f at two points on the LAI vs heat units curve where x proportion of heat units f corresponding proportion of LAI 0 29158 0 2 Ist calibration point on LAI curve r r 0 1 0 1 0 34282 0 8 2nd calibration point on LAT curve r r 0 1 0 1 1 00 plant _LAIDeclineRate s 1 0 01 plant DroughtSensitivity s 62500 plant PlantDensity s pl ha 1 the following two ordered pairs are the x f at two points on the Max LAI vs population density curve where x population density pl ha 1 cf plant PlantDensity f corresponding proportion of maximum LAI attainable at that density 0000 0 2 Ist calibration point on LAI curve r r pl ha 1 0 1 50000 0 8 2nd calibration point on LAI curve r r pl ha 1 0 1 248 plant MaxHeightPerWeight s m kg 1 variables only for Constant crop model only for 4 00 plant _MaxTopDM s kg ha constant 0 00 plant _CanopyMax s kg m2 model 0 0 plant_BaseTemp s degrees C Save file save def GAPS 3 0 save file with the default values The save file must be saved with the extension SAV Lines starting with the sign are ignored at input Comments added after the input data preceded by a are also ignored 1 integer Number of hours n to save followed by n lines with the hours i 0 23h NumberOfHo
85. 3 default 1 2 PartDensity s Mg m3 default 2 6 HydCon s kg s m3 default 0 003 AirEntryPot s J kg default 0 3 BValue s default 7 8 InitWater s default 1 gt if 1 value is replaced by DUL DUL s default 0 3 DLL s default 0 1 InitSoilTemp s C default 20 Clay s cg kg default 25 Silt s cg kg default 25 SatWaterCon s default 1 gt if 1 value is replaced by 1 BulkDensity PartDensity CoarseFrag s default 0 LowBound BulkDensity PartDensity HydCon AirEntryPot BValue InitWater DUL DLL InitSoilTemp Clay Silt 0 010 350 2 650 0 00300 0 30 7 80 0 283 0 283 0 143 0 0 500250 0 050 350 2 650 0 00300 0 30 7 80 0 283 0 283 0 143 0 0 25 0 50 0 150 350 2 650 0 00300 0 30 7 80 0 283 0 283 0 143 0 0 25 0 25 0 0 300 350 2 650 0 00300 0 30 7 80 0 283 0 283 0 143 0 0 25 0 25 0 0 480 425 2 650 0 00300 0 30 7 80 0 273 0 273 0 143 0 0 25 0 25 0 0 660 500 2 650 0 00300 0 30 7 80 0 218 0 218 0 108 0 0 20 30 20 50 0 840 500 2 650 0 00300 0 30 7 80 0 218 0 218 0 108 0 0 25 0 25 0 1 000 550 2 650 0 00300 0 30 7 80 0 050 0 050 0 010 0 0 25 07 25 0 1 100 550 2 650 0 00300 0 30 7 80 0 050 0 050 0 010 0 0 20 30 25 0 1 300 550 2 650 0 00300 0 30 7 80 0 050 0 050 0 010 0 0 25 0 250 1 500 550 2 650 0 00300 0 30 7 80 0 050 0 050 0 010 0 0 25 0 25 0 GAPS Vorcinn 3 5 Tleer s Manual 144 Plant file example plt GAPS 3 0 s single Global variables Li
86. 40 crop RA s s m 20 crop RCopen s s m 0 60 crop AS s Main crop object variables loaded in croplib crop model Init 0 01 plant LAI s 0 01 plant InitialDryMatter s kg ha 60 plant MaxRootingDepth s m 0 0250 plant SowingDepth s m variables only for Stockle Riha crop model 2 00 plant_CanopyMax s kg m2 1500 plant _CriticalLeafWP s J kg 62500 plant _PlantDensity s pl ha 0 500 plant_HarvestIndex s 540 plant_Kernels per plant i 8 plant Kernel Growth Rate i mg d 7 0 plant CND Power s 0 0 plant_Pmax s mgCO2 m2Leaf sec 0 0 plant P Effic s mgCO2 J 0 0 plant P Curve s 0 plant_PT min s C 0 plant_PT opt s C variables only for Stockle Riha corn model GA PS Vorcinn 3 5 TTeor c Manual 145 3 plant Coeff 1 49 plant Coeff 2 56 plant Coeff 3 58 plant Coeff 4 65 plant Coeff 5 GA PS Vorcinn 3 5 TTeor c Manual 144 Save file example sav GAPS 3 0 save file with the default values The save file must be saved with the extension SAV Lines starting with the sign are ignored at input Comments added after the input data preceded by a are also ignored 1 integer Number of hours n to save followed by n lines with the hours i 0 23h NumberOfHours i Number of days n to save followed by n lines with the days i d 25 NumberOfDays i 270 280 290 Cropping Sequence file e
87. 7 plant_P Effic s mgCo2 J 0 75 plant_P Curve s 0 plant_PT min i C 25 plant Pr Opt 1 C variables only for Stockle Riha corn model 3 plant_Coeff 1 i vegetative 49 plant Coeff 2 pollination 56 plant _Coeff 3 late lag 58 plant _Coeff 4 early filling 65 plant Coeff 5 senescing the following two ordered pairs are the x f at two points on the height vs degree days curve where x degree days AccDD as a proportion of AccDD to pollination f corresponding proportion of MaxHeight 033 0 2 Ist calibration point on height curve r r 0 1 0 1 0 5 0 8 2nd calibration point on height curve r r 0 1 0 1 variables only for Stockle Riha wheat model only for 0 20 plant RowSpacing s m wheat 00 plant_Coeff 1 i emergencd 76 plant_Coeff 2 1 leaf 328 plant_Coeff 3 2 leaves 460 plant_Coeff 4 3 leaves 602 plant_Coeff 5 jointed 744 plant_Coeff 6 5 leaves 886 plant_Coeff 7 6 leaves 028 plant_Coeff 8 8 leaves 170 plant_Coeff 9 flag leaf extended 312 plant Coeff 10 booting completed 454 plant Coeff 11 heading completed 514 plant Coeff 12 flowering completed 892 plant Coeff 13 ripe the following two ordered pairs are the x f at two points on the height vs degree days curve where x degree days AccDD as a proportion of AccDD to booted f corresponding proportion of MaxHeight 0 3 0 2 lst calibration point on height curve r r 0 1 0 1 0 5 0 8 2nd calibration point on height
88. Curve number EPIC runoff nnnnonnnnenensnsensnsoseseseoresorersrsesesesreresesersese 113 5 8 Plant water uptake soil plant mterfacc 115 5 7 1 Potential driven water uptake 116 5 7 2 Plant available water uptake nen 119 5 7 3 EPIC model water uptake ooocoooccocccoccnnconnconnconncnnncnnnnnnnonnnnnnrnnnnnnncnnaoos 121 3 9 Water budget caian a ER u I n O aea 123 5 10 SOM temperature m ee rates Tanner nee wenn da ee 124 5 9 1 Heat e e E Ee 124 5 9 2 Simple harmonic soil temperature ooocoocccocnnnconocnnncnnncnnnnnnnonnnonncnnncnnncnnnos 126 6 CARS for Programmers a add 129 6 1 Changing GAPS MMS tt een ne mania line 129 6 2 Changing GAPS procedures oocoooccocccncnnncnnncnnncnnnonnnnnnnnnnonnnrr rr nnnrnnnnnnnnnnrnnnrnnnnnnnnns 129 PER A E ee 131 1 Introduction GAPS is a General purpose simulation model of the Atmosphere Plant Soil system Its outstanding features include the following 1 It represents soil plant and atmospheric processes in a variety of ways These representations can be selected independently of each other subject to some limitations Thus the model user can compare the effects of different ways of simulating the same phenomena 2 It is menu driven and includes an editing module for preparing data and parameter files 3 It can display graphs during the simulation run as well as after the run is complete allowing a dynamic understanding of the processes being simulated
89. DESQVIEW setup GAPS writes text directly to the screen and displays graphics It does not use serial ports it only uses diskettes if you specify data files on these It does not require or use any extended or expanded memory and it uses its own color schemes not DESQVIEW s GSB can run as a background task under DESQVIEW if you redirect its standard output to a disk file so that it is not writing to the screen while running in the background GA PS Vorcinn 3 5 TTeor c Manual 2 2 2 Installation GAPS is distributed on one 1 44Mb 3 5 diskette one 1 2Mb 5 25 diskette two 720Kb 3 5 diskettes or four 360Kb 5 25 diskettes To install GAPS put the first distribution diskette into a diskette drive connect to that drive e g with the DOS command a or b and type install for example A install Note that there is no harm in running the installation program several times e g to load parts of the distribution that you hadn t loaded previously or to update to a new version You will be presented with a short data entry screen To move around press the Tab key or use the mouse if installed To toggle a selection on or off press the space bar The amount of disk space required for each selection is given on the right of it By default everything is selected and the drive and path where GAPS will be installed is C GAPS3 Specify 1 the drive and path where you want GAPS to be installed th
90. GAPS General purpose Atmosphere Plant Soil Simulator Version 3 0 User s Manual July 1994 Susan J Riha David G Rossiter Patrick Simoens Department of Soil Crop amp Atmospheric Sciences Cornell University Ithaca New York USA GAPS computer program amp documentation Cornell Research Foundation 1994 ALL RIGHTS RESERVED This Software and all copies thereof are proprietary to Cornell Research Foundation and that title shall not pass to the User All applicable rights to patents copyrights trademarks and trade secrets in the Software are and shall remain in Cornell Research Foundation The User shall not sell the Software or copies thereof to others Cornell Research Foundation makes and the User receives no warranty express or implied and there are expressly excluded all warranties of merchantability and fitness for a particular purpose Cornell Research Fundation shall have no liability for consequential exemplary or incidential damages even it is has been advised of the possibility of such damages Correspondence regarding this manual or the GAPS program should be addressed to GAPS Project c o Dr Susan J Riha Department of Soil Crop amp Atmospheric Sciences 140 Emerson Hall Cornell University Ithaca NY 14853 USA Telex WUI 6713054 Attention Riha Soils FAX 607 255 8615 Attention Riha Email sjr4 cornell edu Notice This documentation may be freely copied or translated as long as this page in
91. Kc s 0 1 crop coefficient 20 BLC s W m2 K 0 RainFirst 1 h 24 Rainlast i h 2 50 WindHeight s m 0 Elevation s m 0 15 WorkMaxDepth n s m for n till 1 to traffic 2 0 05 WorkMaxDepth n s m 0 37 WorkLimitWN n s m3 m3 for n till 1 to traffic 2 0 37 WorkLimitWN n s m3 m3 9 08 WorkLimitWP n s J kg for n till 1 to traffic 2 9 8 WorkLimitWP n s J kg 0 05 Depth of evap s m 0 54 CO2ext s g m3 Soil file soil def GAPS 3 0 soil file with the default values The soil file must be saved with the extension SOL Lines starting with the sign are ignored at input Comments added after the input data preceded by a are also ignored s single i integer b boolean s70 string 70 NO NAME SoilName s70 0 78 SwAbs s 0 1 00 78 CN2 i 0 100 0 00 Slope s 2 WUD s 0 10 5 Layer i LastLayer Minimum of Layer and MaxLayer 1 1 layer inputline for n FirstLayer to LastLayer all s LowBound s m BulkDensity s Mg m3 default 1 2 PartDensity s Mg m3 default 2 6 HydCon s kg s m3 default 0 003 AirEntryPot s J kg default 0 3 BValue s default 7 8 InitWater s default 1 gt if 1 value is replaced by DUL DUL s default 0 3 DLL s default 0 1 InitSoilTemp s C default 20 Clay s cg kg default 25 silt s cg kg
92. LastDay i day of year 1 input line for every day MinTemp s C default 0 0 MaxTemp s C default 20 0 SolRad s MJ m2 d default 1 not known if 1 then sim NetRad 0 Precip s mm d default 0 0 RelHumid s default 1 not known Windspeed s m s default 1 not known if 1 then RA crop RA or 90 s m PanEV s mm d default 0 0 VaporDensity s g m3 default 1 not known SnowPack s cm default 0 0 MinT Mast SolRad Precip RelHumid Windspeed PanEV VaporDnsity Snow 0 0 20 0 1 0 0 1 1 0 0 1 0 0 Day 1 january 1 0 0 20 0 sch 0 0 1 1 0 0 0 0 2 0 0 20 0 1 0 0 D 1 0 0 1 0 0 3 0 0 20 0 1 0 0 eh 1 0 0 i 0 0 4 0 0 20 0 1 0 0 1 sii 0 0 lt T 0 0 5 0 0 20 0 0 0 Sl ze 0 0 Sch 0 0 361 0 0 20 0 1 0 0 1 1 0 0 1 0 0 362 0 0 20 0 1 0 0 Ki 1 0 0 Si 0 0 363 0 0 20 0 0 0 Al al 0 0 i 0 0 364 0 0 20 0 1 0 0 I 0 0 1 0 0 365 Location file location def GAPS 3 0 location file with the default values The location file must be saved with the extension LOC Lines starting with the sign are ignored at input Comments added after the input data preceded by a i are also ignored s single i integer b boolean s70 string 70 NO NAME LocationName s70 0 0 Latitude s N or S 43200 TSN s s 28 Alpha s Priestly Taylor coefficient 0 Kp s 0 1 Pan coefficient GA PS Vorcinn 3 5 TTeor c Manual 132A 1 0
93. LeafWP P ant CLWP_Power 2 where NonStressRes s m 1 is the non stressed stomatal resistance calculated in the procedure MaxPhotosynthesis LeafWP is the simulated leaf water potential J kg 1 calculated in the procedure Water Uptake plant CriticalLeafWP is a species dependent empirically derived value J kg 1 and plant S is a species dependent empirically derived constant The reduction in transpiration that occurs due to an increase in stomatal resistance is related to the contribution of stomatal resistance to the total resistance to vapor transport given by Campbell 1977 The ratio of evaporation from leaves with non stressed and stressed resistances PSStressFact is determined by the following relation from Campbell 1977 PSStressFact SSVD PSCON NonStressRes RA Re SSVD PSYCON StressRes RA Re 3 where SSVD is the slope of the saturation vapor density function g m3 Ech PSYCON is the psychrometer constant 0 494 g m3 Kl RA is the daily crop boundary layer resistance s m calculated at the beginning of the day in Daily Growth Begin and Re is the combined resistance for convection and longwave radiation heat transfer from the canopy surface assumed to be a constant 40 s nr Campbell 1977 Knowing the transpiration ratio PSStressFact the simulated actual transpiration ActTrans can be calculated as ActTrans PSStressFact sim PotTrans 4 Then a new simulated leaf water potential LeafWP
94. Manual AA AccTopDryMatter AccTopDryMatter ShootGrowth 11a AccRootDryMatter AccRootDryMatter RootGrowth 11b AccTotalDryMatter AccTotalDryMatter ShootGrowth RootGrowth llc and the rooting depth is determined from the accumulated dry matter RootingDepth 2 07 AccRootDryMatter 0 0427436 AccRootDryMatter 12 and adjusted by calling the ancestor model s LimitRootingDepth procedure The carbon reserve CRes is limited to 1 5 of the total dry matter on the theory that at most this proportion of the structural carbon can be labile CRes Min CRes 0 015 AccTotalDryMatter 13 Finally the current leaf area index LAIJ is determined From emergence until the flag leaf is extended the LAT is a function of accumulated top dry matter LAI LAL K AccTopDryMatter 0 237614 AccTopDryMatter 14a where LAI K adjusts for the effects of row spacing and also includes an empirical growth factor This is computed in the object constructor as LAL K 3 791 1 0 3 plant RowSpacing 100 15 where plant RowSpacing is the row spacing cm Note that this equation corrects for deviations from the standard 30cm rows used to calibrate the model Once the flag leaf is out LAI declines slowly according to real time Ifthe flag leaf is out but the head is not yet in the boot this decline is at the rate of 3 of the maximum LAI LAlatFlagLeafOut per day LAI LAlatFlagLeafOut 0 03
95. Richards Equation water flow method is suitable to use with the Potential driven water uptake method both conceptualizing the soil water in terms of its energy At the beginning of simulation the procedure Richards Equation Init is called to set up the module s private variables In particular this procedure computes the inter node saturated hydraulic conductivities given the layer saturated hydraulic conductivities in the soil input file In the present GA PS Vorcinn 3 5 TTeor c Manual OA implementation the inter node conductivity is simply taken as the lesser slower of the layer conductivities of the layer containing the node and the one below it At each time step the procedure Richards Equation is called to compute the soil water balance This procedure is broken down into a series of sub procedures e Hydraulic Conductivities calculate unsaturated hydraulic conductivities for each layer from the current water potentials e Soil Evaporation compute actual evaporation from the top soil layer e Jacobian set up simultaneous equations for determining new water potentials from the current water potentials and contents and hydraulic conductivities Thomas Algorithm solve this system of equations New Water Contents calculate the new water contents for each layer from the updated water potentials These are called in turn as many times as necessary until the numerical solution of the Richards
96. Shoot Root Ratio in Relation to Models Annals of Botany 61 433 49 GA PS Vorcinn 3 5 TTeor c Manual 134 Appendix A Common problems Run time errors GAPS or GSB may crash i e stop with an internal program error in which case you will see an error message at the top ofthe screen This section discusses the most common of these and which of them may be solved by the GAPS user Run time errors other than those listed below and also some of these are programming errors We would more than appreciate a note from you with the error message program code address like 09AB 137C and a brief description of what caused the crash A printout or diskette with the input files and scenario would help Error 200 Division by zero The denominator of an expression was numerically zero This may result from non physical inputs which cause empirical relations to be evaluated outside their calibrated ranges Error 203 Heap overflow This error is generated as GAPS attempts to allocate dynamic variables on the heap Many of these are generated only for specific GAPS models e g crop objects and soil layers You can avoid this error by recompiling GAPS to allow more heap space Error 205 Floating point overflow The result of a floating point calculation could not be represented in a floating point number This is commonly a result of division by a very small number It may result from non physical inputs which cause em
97. Stress LAIStr kg m2 hr J kg g m2 hr s m 1 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 10 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 20 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 30 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 40 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 50 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 60 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 70 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 80 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 90 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 00 2 0 000 0 000 1500 0 0 00 0 1 00 0 00 0 00 10 2 0 0000 0 0000 1500 0 0 00 0 1 00 0 00 0 00 20 2 0 0000 0 0000 1500 0 0 00 0 1 00 0 00 0 00 30 12 0 0000 0 0000 1500 0 0 00 0 1 00 0 00 0 00 40 12 0 0745 0 0756 1500 0 0 39 3200 1 00 0 00 0 00 50 2 0 0817 0 0828 1500 0 0 35 3200 1 00 0 00 0 00 60 2 0 1001 0 1008 1500 0 0 56 3200 1 00 0 00 0 00 70 12 0 4518 0 4536 1500 0 2433 3200 1 00 0 00 0 00 80 12 0 3697 0 3708 1500 0 2 72 3200 1 00 0 00 0 00 90 12 0 6696 0 6696 1500 0 10 00 3200 1 00 0 00 0 00 200 12 0 5792 0 4212 1500 0 11 71 3200 D 13 0 27 0 00 210 12 0 4504 0 3276 1500 0 11 61 3200 0 73 027 0 00 220 12 0 5116 0 5112 1500 0 ak gee 3200 1 00 0 00 0 00 230 12 0 7225 0 3636 1500 0 3 40 3200 0 50 0 50 0 83 240 12 0 4345 0 2196 1500 0 7 04 3200 0 50 0 50 0 83 Note that PotTrans and ActTrans are in units of kg m2 s in the PLF file 1 2 3 4 5 6 7 8 9 10 11 1 day 7 PS 3600 time step 2 hour 8 Nonstre
98. TTeor c Manual 118 sim WUptake I RootWP sim WP I soil NodeDepth I GR Res I 1 This equation is applied to each layer with a positive root soil resistance and a root water potential greater than 1500 J kel The actual transpiration sim ActTrans for the time step kg m2 sh is set equal to the sum of the uptakes from each layer 5 7 2 Plant available water uptake Plant water uptake from the layers in the soil containing roots i e plant F Root to sim LRoot is allowed to proceed until a lower limit of plant extractable water permanent wilting point soil DLL is reached The root density distribution in the soil profile is used to partition the transpirational demand between soil layers Demand not met in any one layer is transferred to other layers as an additional demand Root densities thus do not limit root water uptake in this simple representation but serve solely to partition transpiration in the soil profile This method accounts for multiple crops The first listed active crop takes up all the water it requests from a layer and so on down the profile lowering the available water content accordingly Then the next listed active crop does the same and so on This is the method used in the ALMANAC competition model Kiniry et al 1992 It assumes that there is no competition per se for water just that all crops extract what they can from the available water in each layer with roots The onset of drough
99. They provide values that are used throughout the other time step processes such as water flow heat flow photosynthesis and evapotranspiration 5 2 1 Function Air temperature This function procedure is called at every time step to determine the mean air temperature C for the time step from the daily values of minimum and maximum measured air temperature provided in the climate input file The current air temperature is determined by fitting a sine function to the maximum and minimum and then interpolating from this function over the time step The daily maximum temperatures clim MaxTemp C are assumed to occur at 1500 hours and minimum temperatures clim MinTemp C at 0300 hours To assure smooth interpolation the minimum air temperature of the following day is used after 1500 hours and the maximum of the preceding day prior to 300 hours The formula used is Am Temperature 0 5 MaxTemp MinTemp Max Temp MinTemp COS m 12 elapsed_hour 15 1 where elapsed_hour is the elapsed hour in the day 0 23 In this formula the factor z 2 ensures a period of 24 hours the factor elapsed_hour 15 ensures a maximum temperature at 1500 hours MaxTemp MinTemp 2 is the mean and MaxTemp MinTemp 2 the amplitude of the cosine function 5 2 2 Computation of solar angles source file atmoslib pas procedures SolarAngle SolarAngle Init SolarAngle Daily SolarAngle Done This module ca
100. Tipping Bucket LowBound Simple_Water_Uptake WaterUptake Bulk density BulkDensity Mg m Sol Temperature Default 1 2 Particle density PartDensity Mg m3 Soil_ Temperature Default 2 6 Saturated hydraulic HydCond kg s m3 WaterUptake Richards_Flow conductivity Matric_Flux_Potential Default 0 003 Air Entry potential AirEntryPot J kg WaterUptake Richards_Flow Mate Flux Potential Default 0 3 B value slope of BValue dimension less WaterUptake Richards Flow moisture release Matric_Flux_Potential curve plotted on a Default 7 8 log log scale Initial volumentric InitWater initial conditions for water content Tipping Bucket Richards Flow Default DUL Matric Flux Potential Field capacity DUL m3 m3 Tipping Bucket volumetric water EPIC_Water_Uptake Is Workable content drained Default 0 3 if flow method is upper limit rn Tipping_Bucket SK_model Soil_moisture_index GA PS Vorcinn 3 5 TTeor c Manual 15 Permanent wilting point volumetric water content lower limit InitSoilTemp Initial soil temperature Clay content lt 2 ul Silt content 2 20 u In the computer code all soil data are in the record soil and so their variable names are prefixed by the record name e g soil SatWaterCon Saturated volumetric water content i e total pore space Coarse fragments SimpleWaterUptake EPIC_Water_Uptake m3 m3 Default 0 1 initial cond
101. _Rate kg m2 s from the profile Drain_Rate Flux LastLayer time_step 2 Next the sub procedure Soil Evaporation is called to remove water by evaporation from the near surface layers reducing the simulated new water contents sim WN Finally the sub procedure Calculate Fluxes is called to calculate the change in water content for the whole profile in this time step and to update the simulated water contents for the next time step Procedure Infiltration This sub procedure is called for each layer with the input variable Flux layer kg m2 being the amount of water moving from the upstream layer which in the case of the surface layer is the atmosphere into this layer First the amount of additional water that the layer can hold Hold kg m2 1s calculated as the amount of water between saturation water content and the current water content Hold WS I WII KgFines I 1 where KgFines kg m2 converts from volume to mass WS is the layer s saturation water content m3 m3 and W is the layer s current volumetric water content m3 m3 If the flux into the layer is greater than the amount the layer can hold flow is assumed to be saturated and the sub procedure Saturated_Flow is called to calculate flux out of the layer and the new water content This sub procedure first determines the amount which can drain from the layer during the time step Drain kg m as Drain Profile SWCON WS I
102. a F TN 1 TN 2 6 where loca F is the weighing factor for the finite difference solution which is set as an input parameter in the location file Finally the soil temperatures for the next time step sim SoilTemp are set equal to those at the end of this time step TN 5 9 2 Simple harmonic soil temperature source file soillib pas procedures Harmonic Soil Temp Init Harmonic Soil Temp Daily Harmonic Soil Temp This method computes the soil temperature at the midpoint of each layer as a simple harmonic function of air temperature and depth It is adapted from the discussion of this problem on pp 223 229 of Monteith amp Unsworth 1990 which is similar to the approach found in Campbell 1977 pp 14 19 The soil is modelled as a uniform 3 dimensional body with respect to its thermal conductivity and the heat source is modelled as a diurnal sine wave of fixed amplitude and mean This is only true for soils with uniform thermal conductances by depth and laterally and uniform water content and for uniform daily maximum and minimum temperatures Obviously these conditions are very rarely met However the model provides a simple visualization of heat flow under these ideal conditions GA PS Vorcinn 3 5 TTeor c Manual 1726 Procedure Harmonic Soil Temp Init is called at the beginning of simulation to compute the time invariant parts of the method These are Omega the frequency of the daily sine wave whi
103. ac TempCoeff PARSun TempPower 8 PSShade TempFac TempCoeff PARShade empPower 9 Because of the way the factor coefficient and power are constructed photosynthesis is somewhat less than PAR Crop photosynthesis for the hour PS g m7 is then obtained by multiplying the photosynthetic rate for sunlit leaves PSSun g m sl by the sunlit leaf area index LA Sun and adding to this the photosynthetic rate for shaded leaves PSShade g m2 sly multiplied by the shaded leaf area index LAJShade this rate then being multiplied by the time steptime_step s to obtain a quantity PS PSSun LAISun PSShade LAIShade time_step 10 In the final section of this procedure a non stressed stomatal resistance to vapor loss is calculated for both shaded and sunlit leaves using Ohm s equation to model CO diffusion from the atmosphere into the leaves PSxxx COext COint RACO RESxxx 11 where xxx refers to either Sun or Shade ResSun is the sunlit stomatal resistance to water vapor transfer s m 1 ResShade is the shadelit stomatal resistance to water vapor transfer s m 1 COext is the atmospheric CO concentration 0 54 g m 3 COint is the CO2 concentration internal to the leaf assumed here to be 0 20 g m 3 RaCO is the leaf boundary layer resistance to CO transfer PSSun is the photosynthesis rate of sunlit leaves g m 2 s 1 and PSShade is the photosynthesis rate of shadelit leaves g m 2 s 1 This equation is r
104. ace attempting to satisfy the total evaporative demand to_evaporate kg m2 expressed as an amount rather than a rate to_evaporate sim PotEva time_step 2 For each layer from the top MinLayer to EvapLastLayer determined in procedure Tipping Bucket Init formula 1 is used to determine the amount of water available for evaporation from the layer Ifthis exceeds the remaining evaporative demand the amount water _evaporated is decreased to the total available for evaporation i e to_evaporate In either case the water is removed from the layer and added to the running sum of actual evaporation sim WN layer sim WN layer water_evaporated KgFines layer 3 sim ActEva sim ActEva water _evaporated time_step 4 and the remaining evaporative demand is decreased accordingly to_evaporate to_evaporate water _evaporated 5 This loop continues until the last layer in which evaporation can occur is reached or until there is no more evaporative demand whichever occurs first Note that according to this model the surface layer dries down to its lowest possible water content before the first sub surface layer dries below field capacity and so forth It is certainly possible that not all the evaporative demand can be met because there is not sufficient evaporable water in the near surface layers It is also possible that not all the evaporable water can be evaporated because of insufficient evaporative demand
105. actional water content m3 m 3 This equation has two parameters SMy m3 m3 and y cm which are determined experimentally for a set of similar soils The Dutch workers determined these values for 13 textural classes more or less corresponding to the 12 USDA classes as follows GA PS Vorcinn 3 5 TTeor c Manual 111 SMo y 0 395 0 1000 0 364 0 0288 0 439 0 0330 0 504 0 0207 0 509 0 0185 0 503 0 0180 0 455 0 0169 0 432 0 0096 0 475 0 0105 0 445 0 0058 0 453 0 0085 0 507 0 0065 0 540 0 0042 The dividing line between light and heavy clay is 65 clay This table should be used with caution in soils with dominance of shrink swell clays soils with high contents of sesquioxides soils with high organic matter contents slaking soils and soils with unusual packing density P M Driessen pp 217 221 in van Keulen amp Wolf 1986 discusses some of the many difficulties in estimating SMy y relations in such soils In summary to determine a critical water content 1 determine a critical water suction in cm of water based on the textural class and weight of machinery If this is expressed in MJ kg potential multiply by 10 2 to obtain cm 2 Select parameters SMo and y from Table 1 based on the textural class of the soil being modelled 3 Calculate according to equation 1 For example 90cm suction head of water in a clay loam corresponds to a moisture content of SM 0 445 e0 0058 In
106. al 4A not be selected by the GAPS user it merely serves as a common ancestor of the submodels maize and wheat in the crop model hierarchy Constructor Init This procedure is called by the simulation driver whenever an object oftype SR_model is created at run time Its purpose is to initialize the state of the crop model Destructor Done This procedure is called by the simulation driver whenever an object oftype SR_model is destroyed at run time Its only purpose is to deallocate the heap space used by the object Public procedure Daily_Growth_Begin This procedure is called by the simulation driver at the beginning of each simulated day It initializes the daily total photosynthesis SumPS and the daily accumulated stress index StressIndex and then calls its ancestor object s procedure of the same name It also computes the canopy resistance to vapor transport RA based on the windspeed if available otherwise from a constant plant RA taken from the plant file as in the Penman Monteith evapotranspiration method for use in the critical leaf water potential method of computing water stress Public procedure TimeStep_Growth This procedure is called by the simulation driver at each time step when the crop is actively growing It is called after determining the current soil temperature and potential evapotranspiration but before the plant water uptake and soil water flow Thus the model has a current estimate of potential ETP b
107. an object oftype SRw_model is created at run time Its purpose is to initialize the state of the crop model Destructor Done This procedure is called by the simulation driver whenever an object oftype SRw_model is destroyed at run time Its only purpose is to deallocate the heap space used by the object Public procedure Daily_Growth_End This procedure is called by the simulation driver at the end of each day It first calls private function Growth Stages to accumulate degree days and possibly move to a new growth stage Then the current day s water stress index accumulated during the day in the Critical Leaf Water Potential or Simple Water Stress procedures is added into the current growth stage s cumulative stress index these will be used to determine grain numbers at flowering If the crop has emerged but not yet done flowering private procedure Dry Matter Accumulation is called to simulate the conversion of photosynthate into dry matter otherwise if the crop is not yet ripe grain yield formation is simulated by calling private procedure Yield Finally the Daily Growth_End of the generic Stockle Riha model is called to accumulate a stress index Public Function GetTransFrac The proportion of light intercepted for this crop as a monoculture is computed according to Stockle 1985 as GetTransFrac 1 exp 0 82 LAD 1 where LAT m2 leaf m ground is the leaf area index of the growing crop GA PS Vorcinn 3 5
108. assumed to be responsive to the moisture environment Since these dynamics are combined with a functional equilibrium approach to GA PS Vorcinn 3 5 TTeor c Manual AR partitioning with respect to supply and demand for water biomass accumulation is sensitive to the water balance in the environment Constructor Init This procedure is called by the simulation driver whenever an object oftype SRt_model is created at run time Its purpose is to initialize the state of the crop model Destructor Done This procedure is called by the simulation driver whenever an object of type SRt_model is destroyed at run time Its purpose is to deallocate the heap space used by the object Private procedure Daily_Growth_Begin This procedure is called at the beginning of each day to initialize daily variables Sum_SoilTemp layer SumWN layer StressIndex and SumPS to 0 Private procedure LimitRootingDepth This procedure does nothing and is called only to override the procedure called at the level of Stockle Riha Procedure Light _Interception Here the simplified method of computing light interception by a plant canopy used at the level of Stockle Riha is overridden to account for the non homogeneity of the canopy in a tree plantation before canopy closure occurs It is based on a model developed by Jackson and Palmer 1979 1981 and assumes canopy units are shaped as ellipsoids with dimensions defined by the daily leaf area index LAI an
109. ater stress The wheat and maize models differ in their growth stages dry matter accumulation and grain yield formation This model can account for winter kill but does not account for vernalization This model has several important differences from the model presented in Stockle s PhD thesis Most notably we do not here attempt to model the nitrogen status of the soil or plant Any equations involving GA PS Vorcinn 3 5 TTeor c Manual AN nitrogen have been simplified by assuming that N is non limiting Other simplifications are 1 degree days are accumulated daily from the average temperature not hourly 2 root growth is not adjusted for the soil water potential 3 no carbon is translocated from the shoot to the grain A key concept of this model is the growth stage The plant is considered to be in one of a set of mutually exclusive stages from planting through harvest The stages control or modify various behaviors of the plant e g the rate of dry matter production The stages are listed in the enumeration data types SRw_GrowthStages and are pre emergence emerged one leaf two leaves three leaves jointed 5 leaves 6 leaves 8 leaves flag leaf extended boot completed heading completed flowering completed and ripe The plant moves from stage to stage according to accumulated heat units as explained in private function Growth Stages Constructor Init This procedure is called by the simulation driver whenever
110. ater uptake Private Procedure Grow_Sinkers This procedure creates the sinker or tap root structure from which new root growth can occur It is only called if today s accumulated photosynthate exceeds the amount required for the daily increment and the sinker roots have not yet reached the bottom of the profile The Sinker_Growth_Rate in units of m day 1s input by the user in the plant file and does not vary as a function of the environment In this procedure the sinker roots are incremented in length and then the layer in which the roots now end is computed in order to update sim LRoot the layer number of the last soil layer with roots In this step the tap root may have reached beyond the edge of a new layer so the amount of biomass to add to each layer s current root biomass is calculated and NewRtBio layer is updated This amount of biomass is calculated as the No of Sinkers per plant input by the user multiplied by the planting density the Sinker_Growth_Rate and the inverse of the length to weight ratio for coarse roots also input by the user in the plant file This quantity is then subtracted from the available photosynthate sumPS Since this procedure is called before the daily partitioning routine is called it implies that the model assumes that root extension growth will proceed regardless of other demands for carbon If the tap root has reached the bottom of the profile it is assumed to continue growing and adding biomass to
111. atric_Flux_Potential_TimeStep end Flow_method summarize water relations for the time step WaterBudget end TimeStep_Procedures From this organization it follows that a particular simulation process e g water flow in the soil may be made up of several procedures each corresponding to a time resolution The several procedures for each module are linked through private state variables shared by the procedures of the module The simulation driver also serves to summarize and report simulation variables in End Daily Procedures GA PS Vorcinn 3 5 TTeor c Manual 35 5 1 1 DepthAndHeight This procedure is called by End Daily Procedures at the end of each day It adjusts the overall maximum rooting depth and maximum canopy height by examining the state variables RootingDepth LRoot and crop CanopyHeight for each crop accessed by its pointer TheCrop The maximum or minimum as appropriate over all crops is used to set the state variables sim RootingDepth deepest rooting of any active crop sim LRoot highest numbered soil layer with roots of any crop and sim CanopyHeight top of canopy for all crops These state variables are then available for non plant procedures e g Penman ETP 5 2 Atmospheric processes This collection of modules simulate processes that occur exclusively in the atmosphere 1 e computation of air temperature solar angle and distribution of precipitation throughout the day
112. aturated vapor VaporDensity g Penman_ETP optional if not density entered will be estimated from the simulated air temperature oe CSC ES EC In the computer code all input climate data are in the record clim and so their variable names are prefixed by the record name e g clim MaxTemp A climate file with all this information for all 365 days in a year requires 30Kb disk space 3 4 1 2 Soil file File suffix sol A soil data file specifies a one dimensional soil profile as a function of depth The layers are numbered from 2 the layer whose upper boundary is the surface to an arbitrary maximum which is layer 19 in the versions of GAPS and GSB as distributed In the soil data file the user specifies the actual last layer which may be between 2 i e a one layer soil and 19 The program itself uses layer 1 for the air and a layer immediately below the last one specified for a lower boundary So in GAPS as distributed a soil profile may have up to 18 layers The number of layers which should be specified by the user depends on two factors the profile description from the field or laboratory and the requirements of the GAPS program The natural approach would be to specify one GAPS soil layer for each sampled layer However in some cases it may be desirable to split a sampled layer into several GAPS layers This is most important when using one of the numerical soil water flow procedures Richards Equation or
113. be defined The slope m 2 was estimated to be 0 05 cm stem area m leaf area with an intercept of zero Delta Area Tree 0 05 New_LA planting dens where Delta_Area_Tree is the change in stem cross sectional area per tree in cm and New_LA m2 leaf area per m2 of ground added yesterday is divided through by the planting density trees m to get leaf area per tree Note that because these units are on a per tree basis you must multiply by the planting densit trees m2 to get stemdiameter cm m2 per leaf area m2 m2 Knowing the amount of stem y 8 GA PS Vorcinn 3 5 TTeor c Manual 73 biomass required to meet the demand for water by the new leaf area allometric parameters are used to calculate the stem biomass corresponding to that area Ln_NewBio aWood bWood In Current_Diam Delta_Diam St_Demand exp Ln_NewBio planting_dens Stembio St_Demand where Ln_NewBio is the natural log of the estimate of stem biomass required kg tree This biomass per tree is multiplied by the planting density to convert it to biomass m ground Then the existing biomass is subtracted to get the updated demand for stem Ar Demand Since the demand for each day may not always be met with new stem biomass the balance is carried over from day to day and added to the new stem demand If there is sufficient photosynthate available to meet the sum of the demands for root and stem biomass each plant part is allocated i
114. can be produced on a wide variety of printers As distributed the printing output is directed to a TEXT file To change the printer setting select the Printer Setup option in the File menu You will be shown a list of printers select the one that is actually attached to your system GAPS assumes that the printer is DOS device LPT1 Usually this is associated with the first parallel port If your printer is actually connected to another port you will have to use the DOS assign command to associate the logical device LPT1 with the physical device to which the printer is attached For example the command assign lptl com2 will direct GAPS printer output and any other that uses LPT1 to the second serial port GAPS does not set any communications parameters for serial ports so these should be set up with the DOS mode command you d have to do this for other programs as well 2 4 Monitors If you have a graphics adapter but a monochrome monitor the autodetection logic used by the Turbo Pascal run time library will think that a color monitor is installed and you will be unable to see things correctly on the screen This is often a problem with laptops and other computers with LCD screens To tell GAPS to display output in monochrome regardless of the adapter type at the DOS prompt the command SET GAPSMODE MONO You can also put this command in your autoexec bat or a batch file which calls
115. cation Input Data Data File Name C GAPS3 EXAMPLE LOC locationFileNa me Site Name Redwood Co MN loca locationN ame Report Date 5 24 1994 date Report Time 10 42 15 time Latitude 44 53 loca Latitude Time of Solar Noon S 43200 loca TSN Priestley Taylor Alpha 1 26 loca Alpha Pan coefficient Pan_ETP 1 00 loca Kp Crop coefficient Pan_ETP S 1 00 loca Kc Boundary layer conductance E 20 loca BLC First Hour of rain S 0 loca RainFirst Last Hour of rain z 24 loca RainLast Wind height 5 0 loca WindHeigh t Elevation m A 305 loca Elevation Workability requirements for tillage Depth of workability m 5 0 150 loca WorkMaxDepth till Limiting water content m3 m3 0 370 loca WorkLimitWN till Limiting water potential J kg loca WorkLimitWP till Workability requirements for traffic Depth of workability m 0 050 loca WorkMaxDepth traffic I Limiting water content m3 m3 y 0 370 loca WorkLimitWN traffic Limiting water potential J kg 2978 loca WorkLimitWP traffic Depth to which evap can dry to DUL m 0 050 loca depth_of_evap Atmospheric CO2 concentration g m3 0 54 loca CO2ext Soil file printout soil txt GAPS Soil Input Data Soil File Name Soil Name Shortwave absorptivity Runoff Curve number Site slope m m Water use distribution Last Layer Report Date amp Time C GAPS3 EXAMPLE SOL Dickman SL 0 2 1 00 78 0 00 2 0 L2 5 24 1994 at 10 42 25 GA PS Vorcinn 3 5 TTe
116. ch is Q 2r 86 400 Hz and the layer of the soil profile which will be considered to represent the water status of the entire profile for diffusivity calculations Since most of the water and heat flux is near the surface we choose a depth of 10cm which is just below that where evaporation is typically effective and determine which layer of the profile contains this depth this layer is the representative layer KappaLayer Another approach would be to take the average water content of the profile but this would typically give too much weight to deep layers where the temperature wave is attenuated Either approach violates the assumptions on which the method is based anyway Procedure Harmonic Soil Temp Daily is called at the beginning of each day to compute those parts of the method that are reasonably constant during the day The first of these are the surface amplitude and mean value of the temperature wave computed from the air temperature as SurfaceAmplitude SmoothedMaxTemp SmoothedMinTemp 2 SurfaceMean SmoothedMaxTemp SmoothedMinTemp 2 1 where the Smoothed temperatures are 3 day averages centered on the current day Note that this method is really only valid if the driving function i e air temperature is a periodic function with constant amplitude and mean In most climates this is not the case So we approximate this by the 3 day values and accept discontinuities between days Second this procedure
117. changes DP I is found and once again substituted into the Jacobian matrix The soil water potential changes for each layer are calculated as DP I FGauss I CGauss DP I 1 1 except at the bottom boundary where the back substitution is started by DP LastLayer FGauss LastLayer BGauss LastLayer 1 The water potential is updated for each node as follows sim WP I sim WP I DP I 2 except at the bottom boundary where the potential for the dummy bottom layer is set equal to that of the actual last layer of the soil thereby re establishing the bottom boundary condition The new water potentials are not allowed to exceed the air entry potential for the layer When the DP 1 s for all the nodes in the profile become zero the correct values for the soil water potentials have been found Convergence is determined in procedure Jacobian by checking whether the FGauss I s are sufficiently close to zero 5 5 1 5 Sub procedure New_Water_Contents This procedure forms part of the iterative computation of the water status of the soil It is called iteratively after the new water potentials have been determined in procedure Thomas Algorithm to determine the new water contents sim WN for each layer given the updated water potentials according to the following empirical relation from Campbell 1985 sim WN I WS I soil AirEntryPot I sim WP I sotl BValue 1 1 where WS is the saturated water content
118. cluding the copyright notice and this authorization is inluded unchanged This document and all copies of it may not be resold without the express written consent of the Department of Soil Crop amp Atmospheric Sciences Cornell University Ithaca NY 14853 United States of America IBM is a registered trademark of International Business Machines MS DOS and PC DOS are registered trademarks of Microsoft Corp Table of Contents 1 Introduction TEE 1 2 Installing GAPS 2 2 20 12er aaa re nd aliadas is 2 2 1 System Reorements ss osina ae die 2 2 2 ENS O 3 E aa ar HR IHR IRA a NARBE IRA Ihn 4 DAM AMM dl Ra srl RN es e edo o Ate lea eed ale te 4 2 95 Updating input files dadas Le gd NG 5 3 Running CAPS a dd dia 6 li Starting E a osa 6 3 2 Interacting ek GA E 6 3 2 1 WEE 6 3221 Met Status line te hese rn dese at nds nbc nnd reine se 7 3 2 3 VHS deSktop as nn eet NE Sat acaba uni oe ate 7 ENEE ys serail vasa acae A TERN 8 33 1 Files an veces Babe neun inner 8 332 TTT 9 E E A A DEI 9 3 34 E e lea hie EADE seemeneteeibuenys 10 33 3 Rune sarah AAA AUER 10 3 3 Oe ae RN DT nern 10 3 4 The input and output files ooocooccnocnnoconnconncnnncnnnonononnnnnncnnnrnnnrnnnrnncrnnrnnnrnnnnnnnnns 11 34 L Rue id iaa 11 O anna hoe ded ee Zeene 28 FIS The GAPS Simulator an nen nr nis 29 3 5 1 RS EEN 29 E EE 30 4 Runnin E anne rin erneuern sonne 31 S ThE GAPS model ATI es e EES 33 5 1 Structure
119. content at which thermal conductivity rapidly increases This appears to be highly dependent on the clay content of the soil soil Clay Coeff3 1 1 0 2 6 V soil Clay I 100 4 The procedure SoilTemperatutre is called at each time step to compute the heat fluxes and the new soil temperatures by layer This procedure is broken down into five subprocedures which are called in order Boundary Conditions establish temperatures at the upper and lower soil layers Capacitance Conductance determine the thermal capacity and conductances e Jacobian set up simultaneous solution to the heat flow equations e Thomas Algorthim solve this system of equations e Calculate Fluxes determine the fluxes and new temperatures These are now discussed in sequence The subprocedure Boundary Conditions specifies the upper and lower boundary conditions used in the solution to the heat flow equations Heat transfer from the surface of the soil to the air is assumed to be directly dependent on the difference between air temperature and surface soil temperature times a surface boundary conductance loca BLC W m2 kl provided as parameter in the location input file Thus the thermal conductance K W m2 kl across the surface is set to this conductance and the air temperature AirTemp C is the temperature of the upper boundary K MinLayer 1 loca BLC sim SoilTemp MinLayer 1 AirTemp 1 The temperature below the profile is
120. crop The daily increase in rooting depth is calculated as RootingDepth RootingDepth 2 5 plant MaxRootingDepth DeltaHUF where plant MaxRootingDepth is the maximum root depth for the crop RootingDepth is also limited by the MaxRootingDepth and the soil profile depth The daily increase in biomass DailyTotalDM in t ha is calculated as a function of the photosynthetically active radiation PAR and the crop parameter for converting energy to biomass plant_BiomassEnergy in kg m2 ha MI It is adjusted with the crop growth regulating factor CropStressFactor and the CO2 enhancement factor ARatio DailyTotalDM 0 001 plant _BiomassEnergy PAR CropStressFactor ARatio GA PS Vorcinn 3 5 TTeor c Manual 27 Photosynthetic active radiation in turn is estimated as PAR 0 5 TheCompModel MySolRad MyCropl where PAR is the photosynthetic active radiation in MJ m2 the MySolRad function returnes the solar radiation in MJ m See the Competition module for a description of how the solar radiation is divided among multiple crops in the case that there is only one crop in this case EPIC the function is equivalent to the daily solar radiation times this crop s transpiration fraction see function GetTransFrac Daily change in root weight in t ha is computed with the equation DailyRootDM DailyTotalDM 0 4 0 2 AccUnits The daily changes in dry matter are accumulated in AccTopDryMatter AccRootDryMatte
121. ctor via the New statement case Comp_option of Comp_none Int Comp New comp_model_ ptr Init Comp AL ALMANAC Init_Comp New AL_model ptr Init else Init_Comp New comp_model_ptr Init end case The Comp_option variable is set to Comp_none when GAPS is loaded with a const statement in compete pas and then set to this or another option when the sequence file if any is read fileio load_sequence The constructor initializes the object s variables to zero no radiation or transpiration for any crop Destructor Done This destructor is called by the simulation driver as part of its finalization Finalize Dispose TheCompModel Done Its only purpose is to deallocate the heap space used by the object Even though the Pascal procedure is empty the compiler generates additional code to release the correct amount of memory from the heap GA PS Vorcinn 3 5 TTeor c Manual Q1 Public procedure BeginDay This procedure is called by the simulation driver at the beginning of each day when there are any active crop models after solar angles are computed but before any crop events including planting and harvesting Its first purpose is to partition the day s solar radiation among the active crop models In the default no competition model the first active crop gets all the radiation SolRadFrac first_crop TheCrop crop_i GetTransFrac SolRad first_crop clim SolRad real_day SolRadFrac fi
122. d leaf area density LAD and a height to width ratio of 3 1 The area of the shadow cast on a horizontal surface by the canopy given the sun angle for that time step is calculated as Shadow_Area W pi 4 sqrt W2 H cot SolElA where W is the crown width H is the crown height and So EIA is the solar elevation angle Since shadows will overlap at low sun angles a maximum of 100 ground area in shadow is defined The effective leaf area index for purposes of light interception is then calculated as LAI prime plant LAI Shadow_Area This accounts for the fact that there are large areas of the ground with no leaves above them and where there are leaves the leaf area density through which light must filter is much higher than is implied by the assumption that leaf area is evenly distributed in the horizontal dimension A standard Beer s Law analogy is then used to compute the sunlit leaf area from LAI prime LAISun prime 1 Shadow_area EXP K LAI prime K GA PS Vorcinn 3 5 TTeor c Manual AQ Converting back to standard LAI LAISun LAISun_ prime Shadow_area The percentage of ground area in sunlight is calculated here as 1 shadow_area or the area between trees plus the sunlit ground area below the trees Shadow_area EXP K LAI prime This is used to separate evapotranspiration into evaporation and transpiration In the calculation of diffuse light interception LAI prime is used
123. d output files as well as the simulation specifications such as the model procedures The easiest way to create a scenario file is with interactive GAPS set up the simulation run as you wish and then save the scenario file with the Scenario Save scenario menu In addition GSB accepts up to six additional parameters which allow you to override the names of input and output files given in the scenario file This allows you to use a single scenario file to specify the model procedures and invariant data files and a series of variant input and output files If you don t specify file extensions GSB will automatically use the same ones as GAPS as shown above If any ofthe files which are listed as parameters for GSB are not in the current directory you must specify their absolute or relative pathname as well as their name The optional parameters for GSB begin with a hyphen and a key letter which indicates the type of file name being specified and then continue with the actual file name For example c 3aclimate cli GA PS Vorcinn 3 5 TTeor c Manual 21 specifies that no matter what the scenario file says the plant parameters for the third climate should be taken from file aclimate cli Here is an example of a DOS batch file that invokes GSB several times illustrating some of the possibilities un GAPS for five climates with separate outputs quito set specifies model procedures and the plant soi
124. daily rainfall is sufficiently low no runoff occurs Above this value this equation can be viewed either as a two variable function or a family of parameterized one valued functions in either rainfall or retentivity GA PS Vorcinn 3 5 TTeor c Manual 113 The retention parameter s in turn is a daily adjustment of the curve number based on the current water status of the soil s s1 1 FFC FFC ey W FFC 0 where FFC is the day s fraction of field capacity s7 is a static amplitude parameter and wt and w2 are static shape parameters computed at the beginning of the simulation see below The daily fraction of field capacity is computed as a weighted average of the fractions of field capacity of each layer PF Lauer down to meter or the bottom of the profile whichever is shallower LastLayer Ges LayThick yer layer MidPointjayer FFC 5 SS er 3 2 LayThickjayer MidPointj4yer layer 2 where LayThick is the thickness of a layer and MidPoint is its midpoint both expressed in m and computed in the obvious way from the soil layer lower boundaries soil LowBound layer In this expression the denominator normalizes the result and the multipliers of FFC in the numerator give more weight to thicker layers and those nearer the surface The idea is to determine a composite single value representing the water status of the soil the closer to field capacity the more water will run off
125. default 0 0 MaxTemp s C default 0 0 SolRad s Mj m2 d default 1 not known if 1 then sim NetRad 0 Precip s mm d default 0 0 RelHumid s default 1 not known WindSpeed s m s default 1 not known if 1 then RA crop RA or 90s m PanEV s mm d default 0 0 VaporDensity s g m3 default 1 not known SnowPack s cm default 0 0 MinT MaxT SolRad Precip RelHumid WindSpeed PanEV VaporDnsity Snow 12 2 5645 5 3 0 0 44 5 sch 0 0 1 0 0 1 January 1 4 3 2 3 22 0 0 41 2 1 0 0 1 0 0 2 january 2 14 6 0 8 233 e 64 2 sch 0 0 sch 0 0 3 january 3 SEHR 59 3 4 4 04 3 62 0 1 0 0 1 0 0 4 January 4 AO Oo 4 3 VES 1852 1 0 0 1 0 0 5 january 5 20 7 6 2 4 6 ras 67 2 t 0 0 1 0 0 6 January 6 1340 250 6 0 0 1 62 57 ch 0 0 1 0 0 7 January 7 16 9 4 3 5 8 0 0 50 22 1 0 0 1 0 0 8 january 8 9 8 3 6 3 9 0 0 50 4 L 0 0 0 0 9 January 9 D 6 4 4 9 0 0 72 8 1 0 0 1 0 0 361 december 27 13 3 559 DL 0 0 62 4 1 0 0 I 0 0 362 december 28 422 35 ALBO 4 4 0 0 62 4 Sch 0 0 1 0 0 363 december 29 14 7 8 0 8 1 0 0 60 8 1 0 0 ze 0 0 364 december 30 9 2 2 7 1045 0 0 60 2 1 0 0 i 0 0 365 december 31 GA PS Vorcinn 3 5 TTeor c Manual 142 Location file example loc GAPS 3 0 location file Lines starting with the EN s single 1 integer Redwood Co MN LocationName 44 530 Latitude 43200 TSN 26 Alpha sl Kp 0 Kc 2
126. dix E is a tutorial designed to be read at the computer which introduces the user to the main features of GAPS GA PS Vorcinn 3 5 TTeor c Manual 1 2 Installing GAPS 2 1 System Requirements Operating system GAPS requires a computer capable of running one of the Microsoft operating systems MS DOS or PC DOS V3 0 or later or another operating system that emulates MS DOS either directly e g DR DOS or in a compatibility mode e g the vpix program running on Unix 386 CPU GAPS will run on processors of the Intel 8086 family or functional equivalent for reasonable performance we recommend at least a 12MHz 80286 Main memory GAPS requires a minimum 480Kbytes of free RAM but will run faster with more free memory since less swapping of overlays will be required GAPS does not use expanded LIM EMS or extended memory If you have extended memory you might want to set up a RAM virtual disk in this memory and set up GAPS to read and write its data files from this virtual disk Secondary memory The GAPS executable programs and support files require about 900Kb of disk space and so can be installed on 1 2Mb or 1 44Mb diskette as well as on a hard disk with 0 9Mb free space GAPS input files are in the range of 1Kb to 30Kb each a complete year s climate requiring 30Kb is the largest input file the size of the output files depends on the amount of output requested by the user in particular the numbe
127. djusted with 40000 0 8 density curve x2 this and the f2 previous field Maximum height plant_MaxHeightP Default Daily_Growth_End that can be attained erWeight per unit of total s m kg 1 dry matter Constant crop model specific variables Data field Variable name Units of Modules in which field is used measure Maximum top dry plant MaxTop kg ha Begin aa i matter Default 5 Maximum water plant_Canopy Max kg m2 Water Interception on canopy Default 0 3 Base Base temperature plant Base Temp Base Temp ec ally Growth Bnd Growth_End Extinction plant_ExtinctionC Default 0 65 GetTransFrac coefficient oeff Note that rooting depth is specified by two fields of the plant input file explicitly by MaxRootingDepth and implicitly by NRoot The latter depends on the layer boundaries in the selected soil input file The rooting depth is limited by the MaxRootingDepth t and by NRoot the deepest layer for which RootDens is specified in the plant input file A note on the S curve parameters used in Stockle and EPIC for various purposes these are two points on an S shaped curve that predict proportion of some 0 1 as a function of proportion of some other units to the maximum 0 1 If we assume that the S shaped curve is valid any two points should work However it seems best to avoid the tails and look for points where the response variable is between 20 and 80 of maximum A plant
128. dow is a screen area that can be moved resized tiled overlapped and closed More than one window can be open at any time but only one can be active the one you are currently working in The topmost horizontal bar of a window contains a close box on the left the filename in the middle and a zoom box on the right To quickly close the window click in the close box with the mouse To enlarge or shrink the window click in the zoom box The current position of the cursor line column is indicated on the bottom line of the window An asterisk on the left of the line and column numbers indicates the file has been modified since it was opened or last saved The resize corner in the lower right corner of the window allows you to make the window smaller or larger by dragging it with the mouse The contents of a window can be easily scrolled using the horizontal and vertical scroll bars on the lower and right border of the window To scroll one line at a time click the arrow at either end For continuous scrolling keep the mouse button pressed To scroll one page at a time click the shaded area to either side of the scroll box For quickly moving around drag the scroll box to any spot on the bar Without a mouse these actions can be done using the options in the Window menu or their corresponding hot key To scroll the text in a window use the arrow Page Up and Page Down keys Dialogs Most selections in GAPS are made in dialog boxes As wi
129. e 2 5 Updating input files for a description on how to use convert exe 6 Source code We recommend that this be loaded so that you can examine or print the source code which is the final authority on how the program works The source code files require about 720Kb of disk space These files are installed in subdirectory src under whatever directory you specified for the program GA PS Vorcinn 3 5 TTeor c Manual 3 7 Graphics drivers This is a list ofthe seven possible types and you can load any all or none ofthem You must load the one s that correspond to your system s graphics adapter s in order to see run time and post run graphs on the screen However you don t need any graphics drivers to set up simulation runs prepare input files print input and output files print post run graphs or run the batch version of the simulation program Refer to your computer s hardware documentation to determine what kind of graphics adapter is present on your system Each graphics driver requires about 6Kb of disk space When you are done filling in the form select the Install button to proceed with the installation You will be prompted to insert other distribution diskettes if necessary If you don t want to proceed with the installation press the ESC key or select the Quit button 2 3 Printers GAPS produces two kinds of output 1 listings of input and output files and 2 post run graphs The listings
130. e default is c gaps3 The installation program will create this directory if necessary 1f 1t already exists any earlier version of GAPS in the directory will be overwritten 2 GAPS 3 0 executable protected real mode If selected the GAPS 3 0 executable with all the support files needed to run GAPS will be installed The executables and support files require about 600Kb protected mode version or 400Kb real mode version of disk space The installation program determines whether or not your computer can use the protected mode version and installs the correct version of GAPS 3 GSB 3 0 command line executable GSB 3 0 is the command line version of GAPS 3 0 Together with the executable all the necessary files needed to run GSB are loaded 200 Kb of disk space are needed The executable is in real mode so it runs on all PC s 4 Tutorial examples These files require about 200Kb of disk space They are required to complete the tutorial examples in this manual These files are installed in subdirectory tutor under whatever directory you specified for the program 5 Converting program convert exe The conversion program convert exe allows you to update all the input files used in a previous version of gaps older than version 3 0 The soil files of versions older than 2 1 must be converted first using the older converting program sol_conv exe that came with release 2 1 This program requires 60Kb of disk space Se
131. e respective crop models via the virtual access method MySolRad which is defined in the base competition model The second purpose of this procedure is to compute an overall potential transpiration fraction for all crops taken together to be reported with the access function GetTransFrac This is simply the complement of the product of the various crop s interceptions Wallace s equation 10 TransFrac 1 IntFact As Wallace points out this shows that the total light intercepted by the mixture is independent of the individual species heights whereas the individual fractions are not 5 6 Soil water flow processes GAPS provides three ways of modelling the state and fluxes of soil water in the one dimensional soil profile The simplest in terms of both input parameter requirements conceptual view of the soil profile and implementation is the tipping bucket a capacity model based on the CERES maize model Jones and Kiniry 1986 This is an appropriate model if the modeller only has soil data on soil moisture contents at various field moisture states saturation field capacity and permanent wilting point and only needs to know the moisture content by depth GA PS Vorcinn 3 5 TTeor c Manual 05 A more fundamental point of view is taken by the Richards equation model in which water fluxes are driven by potential energy gradients of water This approach keeps track of the soil water potential soil
132. e selected graphs and toggle the grid on or off Status displays the current status of the computer coprocessor memory loaded scenario Specifications displays the current settings input and output files simulation models time specifications and selected graphs 3 3 5 Run The Run menu option causes the simulation to start with the current settings 3 3 6 Window The Window menu contains the window management commands GA PS Vorcinn 3 5 TTeor c Manual In Tile arranges all the open windows one next to the other so that none overlap Cascade stacks all open windows so that the file names are visible and the active window is on top Close all closes all the windows Size Move resizes or repositions the active window in response to the arrow keys To change the size of a window use the arrow keys in combination with the Shift key Press Enter when done With a mouse you can also resize a window by dragging its title bar Zoom resizes a window to the maximum size If already zoomed to the maximum it will restore it to its previous size With a mouse double click the windows top line to zoom it Next makes the next window active Previous makes the previous window active Close closes the active window 3 4 The input and output files 3 4 1 The input files Several kinds of input can be provided to run a simulation in GAPS 1 one or more climates specifyin
133. earranged to solve for RESxxx and also divided by 1 65 to convert from CO to water vapor resistance Campbell 1977 ResSun COext COint PSSun RaCO 1 65 12 ResShade COext COint PSShade RaCO 1 65 13 To obtain the whole canopy non stress resistance to water vapor transfer the sun and shade lit resistances are weighted according to the proportion of sun and shade lit leaf area and added in parallel Stockle and Campbell 1985 GA PS Vorcinn 3 5 TTeor c Manual A7 NonStressRes LAI LAISun ResSun LAIShade ResShade 14 This is an optimization approach to predicting water vapor loss from a plant canopy since there is an implicit assumption that the plant only opens its stomates the amount necessary to achieve maximum photosynthesis and is never losing more water than required to achieve this rate Private procedure Winter_kill This procedure is meant to simulate the potential for death of winter wheat due to cold temperatures The impact of air temperature and snow pack depth are considered A decreasing fraction of the crop is considered to be vulnerable to damage as the daily maximum air temperature temp increases above 17 6 kill temp 1 1 exp 4 0 20 temp 17 Similarly a decreasing fraction of the crop is considered vulnerable to damage as the snow pack is increased kill snow 1 1 exp 4 0 6 snow 2 5 where snow is snow depth in cm
134. ed from the soil water potential HA exp MW sim WPMinLayer R sim SoilTempMinLayer 273 1 GA PS Vorcinn 3 5 TTeor c Manual 07_ where MW is the molecular weight of water 0 018 kg mole sim WP MinLayer iS the simulated soil surface node water potential at the most recent time step J ke R is the gas constant 8 3143 J mole ol and sim Soiltemp is the soil temperature this time step C Once we have the relative humidity HA the evaporative flux sim ActEva kg m s of water from the surface layer is then calculated from this as sim ActEva sim PotEva HA clim RelHumid day 1 clim RelHumid day 2 where sim PotEva is the potential soil evaporation rate kg m2 sh and clim RelHumid is the relative humidity of the air Evaporation during second and third stage drying is controlled by the humidity of the evaporative surface and the liquid flux to the soil surface from deeper soil layers The derivative with respect to time of the evaporative flux sim DEva kg m s2 is calculated for use in sub procedure Jacobian as follows s m DEva sim PotEva MW HA R sim SoilTempMinLayer 273 1 clim RelHumid day 3 5 5 1 3 Sub procedure Jacobian This procedure sets up simulataneous equations for determining new water potentials from the current water potentials and contents The water flux WFlux kg m2 el positive downward in element may be determined from the current
135. edure Growth Stages case SR_PartioningStage of early PartFactor 0 125 DAE mid PartFactor 2 late PartFactor 0 135 DAE end case 2 This factor is in turn used to compute a the ratio PartRatio PartRatio PartFactor 1 PartFactor 3 PartRatio is then used to partition the daily gain in dry matter into top dry matter TopDryMatter kg m2 and root dry matter RootDryMatter kg m2 TopDryMatter DryMatter PartFactor RootDryMatter DryMatter 1 PartFactor 4 or equivalently RootDryMatter DryMatter TopDryMatter Rooting depth RootingDepth cm is empirically related to root dry matter Acevedo 1975 using a piecewise function of root dry matter by current depth GA PS Vorcinn 3 5 TTeor c Manual IR RootingDepth 1174 8 AccRootDryMatter if RootingDepth gt 82 then RootingDepth 7 28 121 3 AccRootDryMatter if RootingDepth gt 165 then RootingDepth 112 6 70 4 AccRootDryMatter 5 The rooting depth is corrected for the depth to which the seed was sowed RootingDepth RootingDepth plant SowingDepth 6 No correction for water stress on partitioning as included in Stockle and Campbell 1985 was used for these simulations When the maximum rooting depth plant MaxRooting Depth as specified in the plant input file is reached the roots are assumed to stop The development of leaf area LAI m leaf m2 ground depends on the growth stage During
136. ely and summed First a maximum photosynthetic rate given the current leaf temperature assumed to be equal to air temperature is computed using Pmax mg CO2 m2sch the maximum rate of photosynthesis Topt the optimal temperature for photosynthesis and Tmin the minimum temperature at which photosynthesis is possible in degrees c These parameters are all species specific and are defined by the user in the plant input file The function PSTempFac is called to compute the temperature factor which varies between zero and 1 and is multiplied by Pmax to get the temperature corrected photosynthetic rate If the air temperature is between Tmin and Topt PSTempFac increases quadratically PSTempFac T T nin CTopr Tmin C 2 opt opt Tmin Below the minimum there is zero photosynthesis and above the optimum it is assumed to be constant at the maximum Thus the possibly harmful effect of exceedingly high air temperatures are not directly reflected in the photosynthesis routine Gross sunlit and shadelit photosynthesis in mg ms is computed as a function of the photosynthetic parameters input by the user plant_P_curve plant_P _effic the modified maximum photosynthetic rate Pmax and the leaf area in sun or shade PSSun 1 2 PARSun Pmax PARSun Pmax 2 4__PARSun Pmax 2 GA PS Vorcinn 3 5 TTeor c Manual sn where the P_curve defines the curvature of the relationship between light and gross photosynthesis as the max
137. emperature function is linear from 1 optimum at 20 C or above to 0 no grain growth at 3 C or below This potential growth is then multiplied by a fixed sink factor of 0 42 GrainDemand 0 42 GrainGrowth 3 and a mass balance is computed as in Dry Matter Accumulation equations 6 9 with the difference that during grain filling the sink term ParallelDemand is computed only from the grain demand ParallelDemand GrainDemand Reserve GrainSaturation T where GrainSaturation is a constant 106 the same as for shoots and the computation of the derivative in 8 changes accordingly With the revised C reserve value CRes obtained by mass balance the actual grain growth are computed as GrainGrowth GrainDemand 0 42 CRes CRes GrainSaturation 10 where the 0 42 factor is the same as for equation 3 The actual growths is accumulated AccYield AccYield GrainGrowth 11a AccTotalDryMatter AccTotalDryMatter GrainGrowth 11c The carbon reserve CRes is limited to 10 of the total dry matter on the theory that at most this proportion of the structural carbon can be labile CRes Min CRes 0 010 AccTotalDryMatter 13 Finally the number of grains GrainNumber can be increased from the number determined at the beginning of grain filling one time procedure GrainNumber if there is sufficient nitrogen In this implementation of the Stockle model we assume that N is never limiting so set the
138. ent growth stage which may be changed by the passage of time or the accumulation of heat units First if the plant has not yet emerged and forty days have passed it is assumed that the seed has rotted in the ground A message is written to the simulation summary file and the growth stage is set to none which stops the crop simulation Next the function checks whether the plant has been killed by frost This occurs when the daily minimum temperature is below 2 2 C and the growing point is above the ground If the plant is killed and there has been no grain accumulation the growth stage is set to none which stops the crop simulation If there is any grain the growth stage is set to mature so that grain drying can continue to be simulated The heart of this procedure is the computation of heat units or accumulated thermal time as implemented in the corn growth model of Stockle and Campbell 1985 and based on data by Coelho et al 1980 The GA PS Vorcinn 3 5 TTeor c Manual SS heat units DD accumulated during each day are computed as a piecewise continuous function of mean daily air temperature truncated to the next lower integral degree C case trunc TMean of 6 20 DD 0 027 TMean 0 162 21 27 DD 0 086 TMean 1 41 28 32 DD 1 33 43 DD 0 083 TMean 3 67 else DD 0 end case 1 This function allows for maximum heat units in the range 28 32 C correspo
139. enu bar at the top the status line at the bottom and the desktop between the menu bar and the status line 3 2 1 The menu bar To activate the menu bar press the F10 function key When activated one of the menu options will be highlighted Use the left or right arrow key to highlight another menu option To deactivate the menu bar press the Escape key or press the F10 key again To select one of the menu options first highlight it and then press Enter Except for the Run option which starts the simulation on selection a submenu will popup with more options Use the up and down arrow keys the End and the Home key to highlight another submenu option within the same menu option Use the left and right arrow keys to popup another submenu Submenu options followed with an arrow lead to another subsubmenu with related options The Escape key brings you back to the previous submenu Options followed by three dots lead to a dialog box Shortcuts To select a menu option simply press the highlighted letter of the menu option in combination with the Alt key If the menu bar is already activated the Alt key can be omitted To select an option within a submenu simply press the highlighted letter of that option Some menu options are followed by a key combination To select those options simply press the key combination e g to cut a selected text from a file press the Shift and Del key together Some of these shortcuts are mentioned on the
140. equation converges i e the mass balance error is less than a pre defined limit of 10 6 kg m2 sl Non convergence is detected by counting the number of iterations and halting the simulation if a pre defined limit of 256 is exceeded Once the new water contents equilibrate by this iterative procedure the sub procedure Calculate Fluxes is called to record the new water contents and related fluxes These sub procedures are now discussed in turn 5 5 1 1 Sub procedure Hydraulic_Conductivities This procedure calculates unsaturated hydraulic conductivities for each layer from the soil water potentials of the most recent time step or the initial soil water potentials at the beginning of a simulation The unsaturated hydraulic conductivity sim K for each soil profile layer is calculated according to Campbell 1974 sim Klayer soil HydCondjayer soil AirEntryPotjayer sim WPlayer Nlayer 1 where soil HydCond is the saturated hydraulic conductivity kg s m3 soil AirEntryPot is the air entry potential J kg sim WP is the soil water potential J ke and the exponent N is computed as Nlayer 2 3 soil BValuejayer 2 where soil BValue is the slope of the water release curve moisture content vs water potential when plotted on log log scale 5 5 1 2 Sub procedure Soil_Evaporation This procedure computes the actual evaporation from the soil surface First the relative humidity HA of the soil surface layer is calculat
141. erStress or Temperature Stress Water stress factor is calculated as WaterStress sumActTrans sumPotTrans and WaterStress lt 1 with sumActTrans the daily actual transpiration daily root water uptake and saumPotTrans the daily potential transpiration The temperature stress factor is estimated with the equation TemperatureStress sin 1 2 AirTemp plant_BaseTemp plant_OptimumTemp plant BaseTemp where plant_BaseTemp is the base temperature for the crop in C and plant_OptimumTemp is the optimum temperature for the crop in C The heat unit factor HeatUnitFactor is computed using the equation HeatUnitFactor AccUnits AccUnits exp plant PointlLAI plant Pointf2LAI AccUnits where AccUnits is the daily heat unit index and plant_Point1 LAI and plant _Point2LAl are parameters of the crop computed during object initialization to fit an S shaped growth curve As soon as the AccUnits is more than the plant_DeclineFraction the LAI is calculated as follows LAI DeclineLAI 1 AccUnits 1 DeclineUnits plant_ LATDeclineRate where DeclineLAl and DeclineUnits are the LAI and the accumulated units at the day the LAI starts to decline and plant _DeclineRate is a crop parameter that governs the LAI decline rate The crop height CanopyHeight is estimated with the function CanopyHeight crop CanopyHeight Sqrt HeatUnitFactor where crop CanopyHeight is the maximum height for the
142. eral equation Y aD where Y is woody biomass in kg tree and D is stem diameter in cm The parameters a and b are often reported in the literature Parde 1980 and are input by the user according to the tree species being modelled In woody biomass aWood bWood In diameter In woody biomass aHeight bHeight In diameter cHeight In Height where aWood and bWood are the parameters relating diameter to tree woody biomass and aHeight bHeight and cHeight are defined for the log transform of the equation relating height m and diameter cm to woody biomass kg tree Y aDPH This equation is inverted to find tree height through time Private procedure Maintain The maintenance procedure computes the maintenance respiration costs of above and below ground biomass as a function of temperature and existing biomass A Ou of 2 is assumed With a reference temperature Tref of 20 C and a standard maintenance factor at the reference temperature MRef a temperature p p corrected maintenance factor MaintFact kg ke day is calculated for each plant part according to the following T_power Tm Tref 10 MaintFact MRef Q je Maintenance Biomass MaintFact where 7m is the mean temperature of the soil layer or atmosphere depending on the plant part and the units for Maintenance are kg biomass per m2 ground per day Maintenance respiration rates for new roots and older suberized roots are assumed
143. ermined that transpiration can not be occurring 1 e sim PotTrans lt 0 In this case the actual transpiration sim ActTrans and the uptake from each layer sim WUptake are set to zero This module makes extensive use of dynamic variables in order to save memory in those cases when this method of water uptake is not selected The dynamic variables are allocated on the heap in procedure WaterUptake Init which is called before simulation begins and deallocated in procedure WaterUptake Done which is called at the end of the simulation We now discuss the two sub procedures GA PS Vorcinn 3 5 TTeor c Manual 116 5 7 1 1 RootWaterPotential This procedure determines the current root water potential Contained within it is the procedure Resistances which calculates the root resistances in each layer Res I The root xylem resistance is assumed to be negligible and therefore the root water potential is the same at all soil depths Rearranging equation 1 to solve for sim RootWP gives Childs 1977 Riha 1984 sim WP NodeDepth GR sim LRoot sim PotTrans Res 1 RootWP sim LRoot 2 i plant FRoot Res i plant FRoot In this program we compute parts of this equation separately In particular SSumRes is the second term of the numerator of 2 and PSumRes is the denominatior of 2 The most complex part of the entire water uptake procedure is the calculation of the resistances at each layer Res I The
144. ernels_Per_Plant Kernel_Growth_Rate plant PlantDensity 10 4 1 where the factor 104 converts from hectares to m2 the Kernels Per Plant is an input parameter in the Ler put p plant file possibly reduced by water stress as explained above the PlantDensity plants hav is an input parameter in the plant file and the Kernel_Growth_Rate is an input parameter in the plant file converted to kg d in the constructor procedure SR Model Init The daily grain yield is accumulated into a total grain yield AccYield AccYield DailyYield 2 and this is limited by the maximum harvest index which is an input parameter in the plant file and the current total dry matter If AccYield AccTopDryMatter gt HarvestIndex then AccYield AccTopDryMatter HarvestIndex 3 Thus the accumulated yield on any given day can never exceed the harvest index times the accumulated dry matter 5 4 2 2 Crop model Stockle Riha wheat source file stockle pas object name SRw model public procedures Daily Growth End End Growth open det file public functions GetTransFrac PSTempFac is active is transpiring has matured check model private procedures Dry Matter Accumulation Yield Winter kill Max Photosynthesis private functions Growth Stages Grain Number This submodel implements specific procedures for modelling a wheat crop It uses the generic Stockle Riha procedures to simulate photosynthesis and w
145. estimates the thermal diffusivity Kappa m2 s71 of the profile using the current water status of the representative layer KappaLayer by linear interpolation in a piecewise linear function with the three known points being the diffusitivities at 0 20 and 40 volumetric water content in a medium textured soil In the current implementation these are fixed at the pairs 0 0 2 x 10 6 20 0 5 x 106 and 0 4 x 106 m ell following empirical data from Campbell 1977 figure 2 7 and Monteith amp Unsworth 1990 table 13 1 Knowing the diffusivity the damping depth m i e depth in the soil at which the wave is exactly n radians out of phase with the surface wave is computed as DampingDepth V 2 Kappa Q 2 Note that by doing this computation only daily we are assuming that the change during one day in the water content of the representative layer is not significant when compared to the other assumptions inherent in this method Procedure Harmonic Soil Temp is called at each time step to determine the soil temperature of each soil layer using the DampingDepth Surface Amplitude and SurfaceMean computed daily as well as the invariant wave frequency Q The temperature of the layer is taken to be the temperature at its midpoint This is determined by first computing the proportion of the damping depth at the node DampingFraction NodeDepth layer DampingDepth 3 and from this the amplitude of the wave at this depth Am
146. ethod for determining unsaturated hydraulic conductivity from moisture retention data Soil Sci 117 311 314 Campbell G S 1977 An introduction to environmental biophysics New York Springer Verlag 159 pp Campbell G S 1981 Fundamentals of radiation and temperature relations Physiological Plant Ecology I Encyclop Plant Physiol New Ser 12A Campbell G S 1985 Soil physics with BASIC transport models for soil plant systems New York Elsevier Childs S W J R Gilley and W E Splinter 1977 A simplified model of corn growth under moisture stress Trans ASAE 20 858 865 Dale R F Coelho D T and K P Gallo 1980 Prediction of daily green leaf area index for corn Agron J 72 999 1005 DeVries D A 1963 Thermal properties of soils p 210 235 in van Wijk W R ed Physics of Plant Environment Amsterdam North Holland Fisher M J Charles Edwards D A and M M Ludlow 1981 An analysis of the effects of repeated short term soil water deficits on stomatal conductance to carbon dioxide and leaf photosynthesis by the legume Macroptilium atropurpureum cv Siratro Aust J Plant Physiol 8 347 357 Foth H D 1962 Root and tap growth of corn Agron J 54 49 52 Fuchs M Campbell G S and R I Papendick 1978 An analysis of sensible and latent heat flow in a partially frozen unsaturated soil Soil Sci Soc Am J 42 379 385 Gardner W R 1960 Dynamic aspects of water availability to plants Soi
147. fWP Default 1500 Planting density plant_Plant plants ha Density Default 62500 Maximum harvest plant Harvest kg dry grain constructor Initializes for yield index Index kg above limits simulated harvest index ground dry End _ growth used to estimate matter yield from dry matter 1f not simulating yield Defaults 0 5 crop_model 0 44 SR_model Number of kernels plant Kernels per_ count constructor Initializes for yield per plant plant Default 570 SR_model Kernel growth rate plant Kernel _ mg d constructor Initializes for yield growth_rate Default 8 SR_model Power factor for plant CLWP_ dimension less Critical Leaf Water Potential critical leaf water Power potential equation Default 7 Maximum rate of plant_Pmax mgCO2 Max_Photosynthesis photosynthesis m2Leaf sec Default 1 0 GA PS Vorcinn 3 5 TTeor c Manual 22 Initial slope of plant P Effic mgCO2 J Max_Photosynthesis photosynthetic response curve Default 0 007 Curvature of plant_P Curve Default 0 75 Max_Photosynthesis photosynthetic response curve Temperature plant_PT_min Default 0 Max_Photosynthesis minimum for photosynthesis C Temperature plant_PT Opt Default 25 Max_Photosynthesis optimum for photosynthesis C Stockle Riha corn model specific variables 1 Varietal plant_Coeff 1 5 Defaults 3 49 SRm_model coefficients 56 58 65 Ze Ist point height heightS_yl as fitted De
148. fault 0 3 SRm_model GetHeight vs GDD curve by compete FitSCurve 0 2 x1 fl 2nd point heightS_y2 as fitted Default 0 5 SRm_model GetHeight height vs GDD by compete FitSCurve 0 8 curve x2 f2 Stockle Riha wheat model specific variables 1 Row spacing plant_Row Spacing m constructor Initializes for dry_matter_accumulation Default 0 20 GA PS Vorcinn 3 5 TTeor c Manual 23 Varietal plant _Coeff 1 13 Defaults 100 Daily_Growth_End coefficients 176 328 460 Growth_Stages 602 744 886 1028 1170 1312 1454 1514 1892 1st point height heightS_yl as fitted Default 0 3 GetHeight vs GDD curve by compete FitSCurve 0 2 x1 fl 2nd point heightS_y2 as fitted Default 0 5 GetHeight height vs GDD by compete FitSCurve 0 8 curve x2 f2 Accumulated stem plant_AccStemDM kg m2 Dry_Matter_Accumulation dry matter Default 0 0142 Accumulated leaf plant AccLeaf DM kg m2 Dry_Matter_Accumulation dry matter Default 0 0193 Daily elongation plant_Sink m d Dry_Matter_Accumulation rate of sinker roots GrowRate Grow_Sinkers Default 0 024 4 Number of sinker plant _NSink Default 3 Dry_Matter Accumulation roots per plant Grow_Sinkers Sinker root length plant LW_Sink m kg Dry_Matter Accumulation to weight ratio Default 10000 Grow_Sinkers Fine root length to plant LW _Fine m kg Drv Mater Accumulation weight ratio Default 13000 Maintain Initial
149. flow Tipping Bucket Tipping Bucket y Flow_me thod Plant water uptake Plant available water SimpleWaterUptake Uptake_ method Field hours not simulated Do_Fiel dHours Maize variation of Stockle Riha crop model Stockle Riha crop model Model options gt Yield Beginning simulation year A EREEREER REAN FIR TheYear First day 1 FirstDay Last day 365 LastDay Maize variation of Stockle Riha Stockle Riha crop model Model options gt gt Crop planted beginning growth on real day 123 gt gt Crop emerged on real day 138 gt Yield GA PS Vorcinn 3 5 TTeor c Manual crop model elapsed day 0 elapsed day 15 1538 gt gt gt 2 gt gt gt gt 22 gt gt KKK Crop Crop Crop Crop Crop Crop silked on real day 221 elapsed day 98 began late lag on real day 234 elapsed day 111 began grain fill on real day 237 elapsed day 1 senesced on real day 251 elapsed day 128 matured on real day 268 elapsed day 145 harvested on real day 296 elapsed day 173 generic crop model summary x xx xxx Accumulated top dry matter kg m2 2 05 AccTopDryMatte E Accumulated root dry matter kg m2 0325 AccRootDryMatt er Yield kg m2 S 0 84 AccGrainYield Grain moisture x 22 91 GrainMoisture Accumulated stress index 19 81 AccStressIndex Acc Degree Days from Emergence to Maturity 62 14 AccDDM Maize variation of Stockle Riha crop model Stockle Riha crop m
150. for sunlit leaves PARSun is assumed to be a function of the proportion of the total transmission coefficient of the atmosphere TTrans that is direct radiation i e 1 DTrans TTrans multiplied by the canopy extinction coefficient K plus the proportion of the total transmission coefficient of the atmosphere that is diffuse radiation 1 e DTrans TTRans PARSun PAR K 1 DTrans TTrans DTrans TTrans 5 The diffuse PAR for shaded leaves PARShade is calculated as a function of the proportion of the total transmission coefficient of the atmosphere TTrans that is the diffuse radiation coefficient multiplied by diffuse transmission coefficient of the canopy Kd plus the scattered irradiance within the canopy Sclrr PARShade PAR Kd DTrans TTrans Sclrr 6 The scattered irradiance Sc rr is estimated as Sclrr 1 DTrans TTrans PAR 0 07 1 1 0 1 LAl e SSOlElA 7 where DTrans is diffuse transmission coefficient of the atmosphere TTrans is total transmission coefficient of the atmosphere PAR is photosynthetically active radiation W m2 LAI is the leaf area index m2 leaves m ground and SSo ETA is the sine of solar elevation angle Private procedure Max_Photosynthesis This procedure is called hourly to calculate the rate of photosynthesis as a function of leaf temperature and irradiance using a non rectangular hyperbola Thornley and Johnson 1990 Sunlit and shadelit rates are calculated separat
151. g box appears Enter the time range and the graphs to view maximum 4 graphs can be displayed Press any key to return to the menu after viewing the graphs Plant flux pops up the open file dialog After selection of a plant flux output file extension plf the PostRun Graphs dialog box appears Enter the time range and the graphs to view maximum 4 graphs can be displayed Press any key to return to the menu after viewing the graphs Climate flux pops up the open file dialog After selection of a climate flux output file extension clf the PostRun Graphs dialog box appears Enter the time range and the graphs to view maximum 4 graphs can be displayed Press any key to return to the menu after viewing the graphs GA PS Vorcinn 3 5 TTeor c Manual Q Settings pops up the Postrun graph settings dialog box Print variables redirects the output to the selected printer instead of graphing the results to the screen If printing is set to text file you will be prompted for a file name Show grid displays the grid on the graphs Show symbols adds symbols to the graphs 3 3 4 Scenario The Scenario menu contains all the options needed to specify the input and output files the models to simulate and the graphs to display at runtime It also contains the commands to view the current selected specifications and status Load scenario pops up the Load Scenario dialog for selection of a scenario file extension set On
152. g the weather on a daily basis 2 a plant specifying various parameters associated with the plant Multipleplant files may be specified in a cropping sequence see 6 below 3 a soil describing a one dimensional soil profile 4 a location specifying various parameters associated with the site being simulated but not a specific soil or a particular year s weather 5 a save specification specifying the kind and quantity of output that you want GAPS to produce during the simulation run 6 a cropping sequence describing multiple crops relay or inter cropping Not all of these input files are necessarily required this will depend on the specific simulation you are attempting These files can be created and edited with the GAPS Editor File New a_file or File Open a_file menu options or by another DOS program e g as output from a spreadsheet macro They may be printed nicely formatted with the File Print a_file menu option The actual file structures can be interpreted by comparing the input file with the appropriate procedures in source file fileio pas along with the structure definitions from global pas You can print the sample input files unformatted supplied with GAPS directly from DOS or a program editor to see their actual structure The following list gives the default DOS file extensions input output procedures in fileio pas and structure names in global pas GA PS Vorc
153. gDD is the number of growing degree days since silking calculated in procedure Growth _Stages During the senescing growth stage leaf area declines from its maximum to zero as a function of time Dale et al 1980 LAI LAI at_leaf_maturity 0 15 real_day leaf maturity_day 10 where leaf_maturity_day is the day of the year on which the plant began to senesce Private procedure Yield This procedure is called at the end of each day after the daily dry matter accumulation has been determined to compute the current grain dry matter and moisture GA PS Vorcinn 3 5 TTeor c Manual 0 The action of this procedure depends on the growth stage If the plant is in the pollination stage the number of kernels per plant may be decreased if there is sufficient water stress PSStressFact If this is lt 0 25 on a scale of 1 no stress to O complete stress the kernels per plant are decreased by 10 Note that this will happen each day there is this much stress The stress factor is computed by one of the procedures Simple Water Stress orCritical Leaf Water Potential depending on whether the user selected the critical leaf water potential method of limiting photosynthesis If the plant is past the lag stage but not yet mature it is considered that photosynthate is actively being translocated to the grain The daily increase in grain dry matter Daily Yield kg m dl 1s then calculated as DailyYield K
154. hat you would not be able to take advantage of future versions of GAPS Second is that other users don t get the benefits of your insights We encourage you to contact us before undertaking any changes both to see if we or someone else might already be working on the same enhancement and to coordinate such changes with us The file newcrop pas presents a skeleton for a crop object that is descendent from the highest level crop model It explains the interfaces expected by the simulation driver GA PS Vorcinn 3 5 TTeor c Manual 13N Acevedo E 1975 The growth of maize Zea mays L under field conditions as affected by its water relations Ph D thesis Univ of California Davis 253 p Bouma J amp van Lanen H A J 1987 Transfer functions and threshold values from soil characteristics to land qualities pp 106 110 in Beek K J Burrough P A amp McCormack D E eds Ouantified land evaluation procedures Enschede ITC Bristow K L 1983 Simulation of heat and moisture transfer through a surface residue soil system Ph D thesis Washington State University Pullman Brouwer R 1962 Distribution of dry matter in the plant Netherlands Journal of Agricultural Science 10 361 76 Buttler I W amp Riha S J 1989 GAPS a general purpose simulation model of the soil plant atmosphere system Version 1 1 User s Manual Ithaca NY Cornell University Department of Agronomy Campbell G S 1974 A simple m
155. ia this function This function is called by crop models to determine their portion of the daily solar radiation Since each competiton model has its own BeginDa y procedure it can allow the default MySolRad to be called GA PS Vorcinn 3 5 TTeor c Manual 02 Public function GetTransFrac This function returns the fraction of total solar radiation that could be used for transpiration i e the fraction that hits the leaves for all crops taken together It is called by the PartitionETP procedure in atmoslib pas to partition total ETP into potential evaporation and potential transpiration The function simply returns the value of the object field TransFrac which is computed in procedure BeginDay of the various competition models Public function GetPotTrans This function returns the potential transpiraton rate for a single crop It is called from the SimpleWaterUptake and EPICWaterUptake time step procedures at the point when these uptake procedures need to know this rate in order to determine how much water is extracted from each soil layer The default no competition competition model gives the crop that portion of the potential transpiration rate that corresponds to the proportion of the solar radiation captured by the leaves of this plant calculated in BeginDay GetPotTrans sim ETP SolRadFrac crop_i Since each competiton model has its own BeginDay procedure it can allow the default Get PotTrans to be
156. icability Two important land qualities in agricultural operations are workability i e whether the land can be tilled and trafficability i e whether agricultural machinery can drive onto the land GAPS can simulate the number of hours per day when a given plant soil atmosphere environment is workable or trafficable GAPS simulates atmospheric and soil processes e g precipitation evaporation water movement in the soil on a less than daily time scale selected by the user This is typically an hour to four hours At each time step the moisture status of the soil by depth is known either in terms of soil water potential if the Richard s Equation or Matric Flux Potential is used to model water flow or in terms of soil moisture GA PS Vorcinn 3 5 TTeor c Manual 710 content if the Tipping Bucket approach is used to model water flow Also in each time period GAPS simulates the solar elevation angle from this it can estimate daylight and twilight hours At each time step GAPS determines whether the soil is dry enough to a sufficient depth to permit field operations If so the length of the time step is added to a daily sum These sums are accumulated and reported on a daily basis in the GAPS sum output file The determination of whether the soil can be worked or trafficked is based on two parameters 1 the depth to which the soil must be dry enough and 2 the critical soil water potential Richards equation
157. ification for each day specified in the output specification Their contents may be printed or graphed using the menu options File Print Layers soil e File Print Soil flux File Print Plant flux File Print Climate flux e Graph Layers soil e Graph Soil flux e Graph Plant flux e Graph Climate flux To see the variables included in these file and their output formats see source file simio pas procedures save_sim_lay_data save sim sol data save sim plt data save am ch data along with the appropriate variable definitions in global pas These files are read and printed by procedures printLayer printPlf printSof printClf of source file printout pas 3 5 The GAPS simulator This screen allows you to control the simulation Typically you will 1 select input files Scenario Input files 2 select the model procedures Scenario Model procedures F7 3 specify the names of output files Scenario Output files 4 specify the time of simulation both its length in days and the duration of each time step Scenario Time 5 specify the viewgraphs you want to see while the simulation is running Scenario Runtime graphs Select graphs F8 and 6 run the simulation Run F9 3 5 1 Run time graphs A major feature of GAPS is its ability to display a dynamic view of up to four out of a possible 40 aspects of the plant soi
158. ily minimum temperature is above the base value the entire day contributes to the heat units which are calculated as heat_units MeanTemp BaseTemp 1 However if MeanTemp is above 30 C this latter value is used instead of the mean This limits the heat units in the case of very warm days In the most general case the daily maximum is above the base and the daily minimum is below it In this case we must integrate a sine wave which represents the instantaneous air temperature over the period of time when this temperature is greater than the base The amplitude Amplitude of the sine wave is MaxTemp MeanTemp and the cutoff value Zeta is sin BaseTemp MeanTemp Amplitude Then the integral is computed as heat_units 1 1 Amplitude Cos Zeta MeanTemp BaseTemp 1 2 Zeta 2 Private Function water_stress This function computes a daily water stress coefficient on 0 1 extreme to no stress from the daily potential evapotranspiration ET the current soil moisture index SM on 0 1 very dry to saturated and a threshold index Threshold It is based on the SORKAM function WATCO First the threshold index is adjusted so that increasing potential ET results in additional water stress according to SORKAM equation 52 AdjustedThreshold Threshold 0 11 0 028 ET 1 If this is above 0 3 there is no stress to any plant process i e water_stress 1 Otherwise the stress is computed as the ratio
159. imum rate Pmax is approached and P_effic _ defines the initial slope of the relationship or the efficiency with which light is converted to photosynthate After converting mg to g crop photosynthesis for the hour is then obtained by multiplying the photosynthetic rate for sunlit leaves PSSun g m2 sh by the sunlit leaf area index LA Sun and adding to this the photosynthetic rate for shaded leaves PSShade g m sh multiplied by the shaded leaf area index LA Shade this rate then being multiplied by the time steptime_step s to obtain a quantity PS PSSun LAISun PSShade LAIShade time_step 10 In the final section of this procedure a non stressed stomatal resistance to vapor loss is calculated for both shaded and sunlit leaves using Ohm s equation to model CO diffusion from the atmosphere into the leaves PSxxx COext COint RACO RESxxx 11 where xxx refers to either Sun or Shade ResSun is the sunlit stomatal resistance to water vapor transfer s m 1 ResShade is the shadelit stomatal resistance to water vapor transfer s m 1 COext is the atmospheric CO concentration 0 54 g m 3 COint is the CO2 concentration internal to the leaf assumed here to be 0 20 g m 3 RaCO is the leaf boundary layer resistance to CO transfer PSSun is the photosynthesis rate of sunlit leaves g m 2 s 1 and PSShade is the photosynthesis rate of shadelit leaves g m 2 s 1 This equation is rearranged to solve for RESxxx and also d
160. in place of LAI in an equation otherwise identical to that described in SR_model Light Interception This version of Light_ Interception is called hourly by the function Get TransF rac for the fast growing tree model Procedure TimeStep_Growth in this procedure the soil water potentials from 5 a m Pre_Dawn_WP layer are stored for use in the root growth routine and Water Interception optional and Max Photosynthesis are called The sub procedure Accum_SoilTemp accumulates time step soil temperatures by layer in order to calculate an average at the end of the day for root respiration Similarly Accum Water accumulates the volumetric water content by layer for computing daily averages elsewhere Private procedure Critical_Leaf_Water_Potential The fast growing tree model uses a variation on the Stockle Riha procedure Critical Leaf Water Potential As in Stockle Riha a stress index WaterStressFact is calculated according to the hourly leaf water potential and CLWP_Power WaterStressFact is used to cut back potential transpiration sim PotTrans Z NonStressRes 1 LeafWP plant_CritialLeafwp P ant_CLWP_Power WaterStressFact SSVD PSYCON NonStressRes RA Re SSVD PSYCON Z RA Re sim ActTrans WaterStressFact sim PotTrans where SSVD is the slope of the saturation vapor density function g m x PSYCON is the psychrometric constant 0 494 g m Kb RA is the crop boundary layer resistance s mi and Re
161. ince the number of layers in which evaporation is effective can t be determined until that time In sub procedure Soil Evaporation the term soil DUL layer P_EvapFrac layer 1 represents a limiting water content below field capacity to which evaporation can dry the layer n b the layer can dry to field capacity simply by drainage The evaporation fractions P_EvapFrac are the fractions on 0 1 of field capacity to which each layer can be dried by evaporation Now we discuss how these are determined Both calculations begin with one input parameter loca depth_of evap m which is the user defined depth to which the soil can be dried to or below the drained upper limit by evaporation This depth should be based on observations of the soil after it has drained and been subject to evaporation for several days The default value is 0 05m 5 cm The evaporation fraction is a single value for the entire layer however its calculation is based on a continuous function of evaporative potential by depth At the soil surface we assume that evaporation could dry the soil completely i e at a depth of 0 m the evaporation fraction is assumed to be 0 At the maximum depth to which evaporation is effective evaporation can dry the soil only to field capacity i e at a depth of loca depth_of evap m the evaporation fraction is assumed to be 1 We want to fit a continuous function between these two points and we choose a logarithmic
162. inciples of environmental physics 2nd ed New York American Elsevier Nakayama K and A Nakamura 1982 Estimating potential evapotranspiration by the Priestley Taylor model J Agr Met 37 297 302 Norman J M 1982 Simulation of microclimates In Biometeorology in integrated pest management New York Academic Press Parde J 1980 Forest Biomass Forestry Abstracts 41 343 62 Penman H L 1948 Natural evaportion from open water bare soil and grass Roy Soc London Proc Ser A 193 120 146 Pook E W 1985 Canopy Dynamics of Eucalyptus marginata Hook III Effects of Drought Australian Journal of Botany 33 65 79 Priestley C H B and B J Taylor 1972 On the assessment of surface heat flux evaporation using large scale parameters Mon Weather Rev 100 81 92 Rauscher H M J G Isebrands G E Host R E Dickson D I Dickmann T R Crow and D A Michael 1990 ECOPHYS An ecophysiological growth process model for juvenile poplar Tree Physiology 7 255 81 Riha S J 1985 Estimating water fluxes in Douglas fir plantations Can J of For Res 5 701 707 Ritchie J T amp Crum J 1989 Converting soil survey characterization data into IBSNAT crop model input pp 155 167 in Bouma J amp Bregt A K eds Land qualities in space and time Wageningen PUDOC Ritchie J T J R Kining C A Jones and P T Dyke 1986 Model Inputs In Jones C A and J R Kiniry eds 1986 CERES Maize A simu
163. inn 3 5 TTeor c Manual 11 1 climates default file extension cli i o procedures load_climate structure climate_info 2 plants default file extension plt i o procedures load crop options in plant and the crop object Inits structure plant info 3 soil default file extension sol i o procedures load_soil structure sol mio 4 location default file extension loc i o procedures load location structure location_info 5 save specification default file extension sav i o procedures load_save structure save_output_info 6 cropping sequence default file extension seq i o procedures load_sequence structure dates and g seg q 1 0 p _seq plantFileNames The order and format of the data in the input files is important Comments can be added preceded with a sign All characters on an line following a sign are ignored at input Empty strings must be replaced by a sign eg when no save file is selected The data are followed by their variable name datatype and units of measure Since GAPS allows you to select which model procedures to include in a simulation you may not need all of these files or you may not need to fill in certain fields in a file For example if you are simulating the soil water balance under fallow i e no crop is being simulated you would not need to specify a plant file If you are simulating
164. is method of computing ETP has the least data requirements of the four methods found in GAPS The daily mean air temperature TMean C is calculated as TMean clim MinTemp real_day clim MaxTemp real_day 2 1 where clim MinTemp and clim MaxTemp are the measured daily minimum and maximum air temperatures in C Then daily potential evaporation ETPdaily is calculated as ETPdaily 700 Tm 100 ABS loca latitude 15 TMean Td 80 TMean 2 where Td is the dew point temperature C loca latitude is latitude Mean is mean temperature C and 7m is a factor which compensates for elevation computed as TMean 0 006 loca elevation 3 where loca elevation is the station elevation in m from the location input file The daily evaporative demand ET Pdaily is then distributed over the day using a sine function The instantaneous rate of potential evapotranspiration sim ETP kg m sly is computed as sim ETP 2 3 ETPdaily 0 05 POW SIN 0 0175 7 5 ellapsed_hour 4 secs in day 4 where ellapsed_hour is the elapsed time in a day h and secs_in_day is 86 400 s If the sine of the solar elevation angle is less than 0 sim ETP is set to 0 5 3 5 Partitioning evapotranspiration This procedure is called by the simulation driver each time step after the rate of potential ETP sim ETP has been determined by one of the four methods listed above It partitions the estimate
165. is the combined resistance for convection and longwave radiation heat transfer from the canopy surface assumed to be a constant 40 s m Campbell 1977 A separate photosynthesis stress index PSStressFact is calculated in the same manner but taking the differential diffusion rates of CO and H O into consideration by dividing the resistances by 1 65 PSStressFact SSVD PYSCON NonStressRes 1 65 RA Re GA PS Vorcinn 3 5 TTeor c Manual 7A SSVD PSYCON Z 1 65 RA Re Note that in the other versions of Stockle Riha crop model this distinction is not made for purposes of reducing photosynthesis and PSStressFact is set equal to WaterStressFact Private procedure TimeStep_Stress In this procedure either SRt Critical Leaf Water PotentialorSimple Water Stress are called depending on which was selected by the user Then Limit Photosynthesis is called to multiply PS the timestep potential photosynthesis by PSStressFact Private procedure Dry_Matter_Accumulation This procedure contains six subroutines and is called at the end of each day to calculate maintenance respiration suberization of roots growth of sinker roots partitioning of photosynthate to roots stem and leaves and distribution of biomass above and below ground Throughout this section allometric equations defining the relationship between stem diameter and woody biomass or tree height are utilized Log transformations are made of the gen
166. isk of runoff is much higher at such sites The curve number for moist conditions is then adjusted for site slope according to the empirical equation CN2s CN 1 3 CN3 CN2 1 2 e 13 86 soil Slope J 5 GA PS Vorcinn 3 5 TTeor c Manual 114 where soil Slope is the site slope m ml The effect of this equation is to increase the curve number exponentially with a low coefficient as slope increases The factor CN3 CN2 along with equation 4 ensures that CN2s does not increase past 100 Note that even at zero slope there is some adjustment in fact CN is decreased if CN2 was not the maximum of 100 This is because CN is considered to represent CN at sites with a 0 05 m ml slope Using the adjusted curve number for moist conditions a curve number CN7 for dry conditions is derived using the empirical equation CN CN2s 20 100 CN25 100 CN25 e 0 0636 100 CN J 6 I won t try to explain this equation If the resulting value of CN7 is less than 0 4th of CN2g it is set to this value This sets a floor on CN ensuring that there is still a reasonable chance of runoff even in dry conditions With CN 2 3 in hand we can proceed to compute the shape parameters wz and w2 These are obtained from a simulataneous solution of equation 2 with three known points at FFC 1 0 we want the retention parameter s to be its value for wet conditions i e s3 at FFC 0 5 we
167. itions for Soil Temperature evaporation procedures of Richards Equation Matric_Flux_Potential C Default 20 cg kgofthe Soil_Temperature fine earth fraction Default 25 not used in any currently implemented module included for completeness cg kel of the fine earth fraction Default 25 Tipping Bucket Richards Equation Matric Flux Potential m3 m3 Default 1 BulkDensity P artDensity m3 m3 Default 0 The disk space required for a soil file depends on the number of layers and the data recorded for each layer The maximum size of a soil file is 3 5Kb GA PS Vorcinn 3 5 TTeor c Manual Ta 3 4 1 3 Location file File suffix loc A location refers to a place on the earth s surface without reference to the soil or crop At a given location there are typically a variety of soils and experimental treatments on the various soils Defaults for all variables are set in procedure clear_location source file fileio pas The location input data file contains the following parameters 11 Location name LocationName In 1 O u Time of solar noon Pan coefficient conductance Alpha factor for Alpha Priestly Taylor equation BL NorS Default 0 S Default 43200 Hour of day rain RainFirst h 0 24 or irrigation starts Default 0 Hour of day rain or RainLast h 0 24 irrigation stops Height above canopy
168. ivided by 1 65 to convert from CO to water vapor resistance Campbell 1977 ResSun COext COint PSSun RaCO 1 65 12 ResShade COext COint PSShade RaCO 1 65 13 To obtain the whole canopy non stress resistance to water vapor transfer the sun and shade lit resistances are weighted according to the proportion of sun and shade lit leaf area and added in parallel Stockle and Campbell 1985 NonStressRes LAI LAISun ResSun LAIShade ResShade 14 This is an optimization approach to predicting water vapor loss from a plant canopy since there is an implicit assumption that the plant only opens its stomates the amount necessary to achieve maximum photosynthesis and is never losing more water than required to achieve this rate Private procedure Limit_Photosynthesis This procedure is called every hour to limit the photosynthetic rate PS g m sh calculated in procedure Max Photosynthesis according to the stress factor PSStressFact calcaulated in procedure Critical Leaf Water Potential ifthe Critical Leaf Water Potential simulation option was selected by the model user or Simple Water Stress otherwise as follows PS PS PSStressFact This procedure is redefined in the maize model see below to also stress the LAI GA PS Vorcinn 3 5 TTeor c Manual al Private procedure Critical_Leaf Water_Potential This procedure is called at each time step to compute the stress coefficient
169. justed by a temperature function TFG on 0 1 which relates growth to optimal and sub optimal temperature TFG TOpt exp 1 023 TMeanK TOpt TMean TMeanK 3 GA PS Vorcinn 3 5 TTeor c Manual oi where TMeanK is today s mean temperature K TMean is today s mean temperature C and TOpt is the optimum temperature C for growth which is considered to be 25 C for shoots and 20 C for roots Thus the potential growth is adjusted as ShootGrowth ShootGrowthMax TFG 25 4a RootGrowth RootGrowthMax TFG 20 4b These potential growth rates are then multiplied by a partitioning factor which adjusts the demand for growth in the two sinks These are both a fixed fraction of 0 42 ShootDemand 0 42 ShootGrowth 5a RootDemand 0 42 RootGrowth 5b With the sources photosynthate NetPS and C reserve InitReserve set equal to CRes and sinks shoot and root demand and residual C reserve Reserve we then compute a mass balance FRes as FRes NetPS InitReserve Reserve ParallelDemand 6 where ParallelDemand kg m2 represents the total demand for C computed as ParallelDemand ShootDemand Reserve ShootSaturation RootDemand Reserve RootSaturation 7 where the Saturation are C saturation constants fixed at 10 6 for shoots and 10 for roots implying that the shoot demand contributes about an order of magnitude to the total demand more than the root demand
170. kept constant at the initial soil temperature of the last layer i e the soil temperature at this depth is considered to be constant which is a reasonable estimate in soils deeper than about 1 meter sim SoilTemp soil LastLayer 1 soil InitSoilTemp soil LastLayer 2 The subprocedure Capacitance Conductance uses the empirical coefficients calculated in the procedure SoilTemperature Init and the current water status of the soil to determine the thermal conductance and heat capacitance for each layer The heat capacitance CP MJ m2 ke sl is calculated multiplying the volumetric specific heats of soil SpecHeatSoil 2 4 MJ m3 Kl and water SpecHeatWater 4 18 MJ m3 Kl by the fraction of the soil volume currently occupied by the mineral soil and soil water water respectively and normalizing by the layer thickness LayThick m and time step CP I SpecHeatSoil soil BulkDensity I soil PartDensity I SpecHeatWater sim WN I LayThick I time_step 3 where the term soil BulkDensity I soil PartDensity I is the volume fraction of the soil taken up by mineral soil and sim WN is the current volumetric water content GA PS Vorcinn 3 5 TTeor c Manual 195 The equation used to estimate the soil thermal conductance KI W m2 ol from the empirical coefficients and water content is taken from McInnes 1981 K I Coeff1 1 Coeff2 1 sim WN I Coeff1 T Coeff4 I exp Coeff3 1
171. l location and save specification quito ccuec0001 oclsl quito ccuec0002 oc2sl quito ccuec0003 oc3sl q q n uito ccuec0004 oc4sl uito ccuec0005 oc5sl ow use a different soil at the same location for the same set of climates This soil is described in file FILZ Self quito sj3 ccuec0001 ocls2 quito sj3 ccuec0002 oc2s2 quito sj3 ccuec0003 oc3s2 quito sj3 ccuec0004 oc4s2 quito sj3 ccuec0005 oc5s2 there are now ten output files You may also run GSB from another DOS program using the exec system call This is a convenient way to run large numbers of simulations the control program builds the command line for GSB and then executes it The batch simulations should not be used blindly Use the interactive GAPS to explore several of the combinations and ensure that the simulations are doing what you expect Then you can use GSB to run large numbers of closely related simulations GA PS Vorcinn 3 5 TTeor c Manual ER 5 The GAPS models The core of GAPS is the set of simulation modules These provide a flexible framework for simulating the atmosphere plant soil system Modules may be selected and combined according to 1 input data requirements 2 components of the system that will be simulated and 3 desired model of a system component We encourage GAPS users to examine the source code for each module To this end each section of this chapter begins with a list of the mod
172. l Sci 89 63 73 GA PS Vorcinn 3 5 TTeor c Manual 131 Gardner W R and C F Ehlig 1962 Some observtions on the movement of water to the plant Agron J 54 453 456 Gates D M 1980 Biophysical Ecology New York Springer Verlag Gerik T J Rosenthal W D amp Duncan 1988 Field Crop Res 19 63 79 Hesketh J and D Baker 1967 Light and carbon assimilation by plant communities Crop Sci 7 285 293 Hillel D 1980 Introduction to soil physics Orlando Academic Press Hillel D 1980 Fundamentals of Soil Physics New York Academic Press Hofstra G and J D Hesketh 1969 Effect of temperature on the gas exchange of leaves in thelight and dark Planta 85 228 237 Jackson J E and J W Palmer 1979 A Simple Model of Light Transmission and Interception by Discontinous Canopies Annals of Botany 44 381 83 Jackson J E and J W Palmer 1981 Light Distribution in Discontinous Canopies Calculation of Leaf Areas and Canopy Volumes Above Defined Irradiance Contours for use in Productivity Modelling Annals of Botany 47 561 65 Johnson I R 1990 Plant respiration in relation to growth maintenance ion uptake and nitrogen assimilation Plant Cell and Environment 13 319 28 Jones C A and J R Kiniry eds 1986 CERES Maize A simulation model of maize growth anddevelopement College Station TX Texas A amp M University Press 194 pp Jones C A J T Ritchie J R Kining and D C Godwin 1986 Sub
173. l atmosphere system as this is being simulated You can select up to four run time graphs at a time using the Scenario Runtime graphs Select graphs menu option or by pressing F8 There is also a second selection screen because only 42 options will fit on a screen You access this screen using the Scenario Runtime graphs More graphs menu option The graphs selected with this screen also count towards the four graph limit If more than four graphs are selected on the two screens the first four in order of appearance on the screens will be shown and saved in the scenario file GA PS Vorcinn 3 5 TTeor c Manual 20 3 6 Scenarios File suffix set GAPS makes it easy to re run simulations by allowing the program user to save the set of model procedures input and output file specifications view graphs simulation dates and time step in a scenario file The Scenario menu option Save scenario is used to save the scenario you are asked for a file name the extension set is automatically appended and GAPS writes the simulation specifications to this file To re run a simulation select menu option Scenario Load scenario and then select an existing scenario file from the list that is presented This file will be read setting the simulation options and in addition the input files named in the scenario file will be read into memory At this point menu option Run will start the simulation A scenari
174. l evapotranspiration can be written as sim ETP loca ALPHA NetRad G SSVD SS VD PSYCON LAMB 1 where sim ETP is the simulated potential evapotranspiration kg m2 s loca ALPHA is the Priestley Taylor factor 1 08 to 1 50 NetRad is the net radiation W m2 G is the soil heat flux W m2 SSVD is the slope of the saturation vapor density function kg m3 K PSYCON is the psychrometric constant 0 494 g m 3 K 1 and LAMB is the latent heat of vaporization of water 2450 J g 1 at 20 C Net radiation NetRad W m 2 is calculated as NetRad LWR SwAbs clim SolRad 11 574 SpaRad SpaceSum 2 where LWR is net longwave radiation W m 2 soil AS is the short wave absorptivity of the soil surface default 0 78 clim SolRad is measured solar radiation MJ m2 al being converted to W m2 by GA PS Vorcinn 3 5 TTeor c Manual TR multiplication with 11 574 1 86400 s dl 1 000 000 SpaRad is the theoretical solar radiation above the atmosphere for a given time step W m2 calculated in module SolarAngles and SpaceSum is the theoretical solar radiation for a day W m calculated in module SolarAngles Net longwave radiation LWR W m 2 is calculated assuming the soil or plant surface is equal to air temperature LWR EA ES ST AirTemp 273 4 3 where EA is the long wave atmospheric emissivity ES is the long wave emissivity of the soil or canopy surface constant 0 97 ST is the Stephen Bolt
175. lation model of maize growth anddevelopement College Station TX Texas A amp M University Press 194 pp Rosenthal W D Vanderlip R L Jackson B S amp Arkin G F 1989 SORKAM a grain sorghum crop growth model TAES Computer Software Documentation Series MP1669 College Station TX Texas Agricultural Experiment Station Rossiter D G 1991 Modern computer programming techniques for environmental simulation modelling SCAS Teaching Series 1 Ithaca NY Department of Soil Crop amp Atmospheric Sciences Cornell University Sharma M L 1985 Estimating Evapotranspiration Advances in Irrigation 3 213 281 Shaw E M 1988 Hydrology in practice 2nd ed London Van Nostrand Reinhold International Shinozaki K K Yoka K Hozumi and T Kira 1964 A quantitative analysis of plant form the pipe model theory II Further evidence of the theory and its application in forest ecology Japanese Journal of Ecology 14 133 39 GA PS Vorcinn 3 5 TTeor c Manual 132 Spitters C J T amp R Aerts 1983 Simulation of competition for light and water in crop weed associations Aspects of Applied Biology 4 467 483 Shuttleworth W J and I R Calder 1979 Has the Priestley Taylor equation any relevance to forest evaporation J Appl Meteorol 18 639 646 Stewart R B and W R Rouse 1977 Substantiation of the Priestley Taylor parameter for potential evaporation in high latitude J Appl Meteorol 16 649 650 Stoeckle C
176. lculates the solar elevation angle for any given latitude day of the year and hour of the day First the solar declination angle angle which the sun s rays make with the earth s equatorial plane is calculated knowing the day of the year Then the solar elevation angle is calculated on an hourly basis from the solar declination angle latitude and time of day in relation to solar noon when the sun is directly north or south of the point of observation Knowing the solar elevation angle and the solar constant i e the mean annual radiant flux density outside the earth s atmosphere and normal to the solar beam 1360 W m2 the theoretical irradiance above the atmosphere can be estimated The irradiance above the atmosphere SpaRad W m7 at any time during the day can be calculated according to Campbell 1977 GA PS Vorcinn 3 5 TTeor c Manual Ze SpaRad SinElevAngle SolarConstant 1 where SolarConstant is the solar constant 1360 W m2 and SSo EIA is the sine of the solar elevation angle at the time of the day In turn the sine of the solar elevation angle SSo ElA for any time of the day can be calculated as Campbell 1977 1985 SinElevAngle SolDcA sin loca Lat 0 01745 cos loca Lat 0 01745 cos 0 2618 Time loca Tsn 3600 CSolDcA 2 where SolDcA is the sine of the solar declination angle CSo DcA is the cosine of the solar declination angle loca Lat is the latitude loca Tsn is the time of solar noon
177. leaf area and the daily leaf dry matter accumulation The specific leaf area SpecificLeafArea is computed from the daily mean temperature and PAR by SORKAM equation 37 as SpecificLeafArea MeanTemp 10 1 0 00178 MeanTemp 0 000809 MeanTemp PARInt 0 0308 4 where the factor 1071 converts from cm gl to m2 kel This specific leaf area is then decreased by water stress In SORKAM this is done for each leaf individually in procedure LEAF here we apply the same principle to the entire top The SLA is decreased linearly from its value as calculated in 4 at soil moisture indices gt 0 5 no significant stress to no new leaf area at SMI 0 SpecificLeafArea SpecificLeafArea 2 SMI if SMI lt 0 5 5 The SLA is limited to at most 40 This is then used to determine LAI LAI LAI SpecificLeafArea DailyLeafDryMatter 6a In growth stage 3 the LAI is constant i e from end of leaf growth to anthesis In stage 4 i e during grain filling the LAI declines linearly by the base 1 C heat units LAI LAI LAlLossIn4 GDD_4_to_5 DailyUnits1 6b where LAlLossIn4 is the amount of LAI lost for each heat unit a constant 0 4 normalized by the base 1 C heat units needed to go from anthesis to physiological maturity a constant 880 The LAI must be non negative GA PS Vorcinn 3 5 TTeor c Manual 22 5 4 4 Crop model CONSTANT source file constant pas object name SC model public pr
178. librium evapotranspiration to predict ETP The proportionality factor is supposed to compensate for the elimination of the aerodynamic component from the Penman equation see the description of the Penman module Despite the empirical nature of the proportionality factor ALPHA the Priestley Taylor equation is based on reasonable physical grounds It reduces input data requirements and can be used in situations where wind speed data and therefore aerodynamic resistances are not available It also does not require knowing relative humidity vapor density Priestley and Taylor experimentally determined an average value for ALPHA of 1 26 which is supported by the observation that the radiation component is generally four to five times as large as the aerodynamic component An ALPHA very close to this value has since been confirmed by several investigators Stewart and Rouse 1977 Davies and Allen 1973 when water supply to the evaporating surface is not a limiting factor To improve estimates under advective conditions several attempts were made to estimate ALPHA from available climatic data such as air temperature Jury and Tanner 1975 or air temperature and net radiation Nakayama and Nakamura 1982 Others attempted to correlate ALPHA with soil surface moisture Davies and Allen 1973 The Priestley Taylor equation has also been used to predict evapotranspiration from forests Shuttleworth and Calde 1979 The Priestley Taylor equation for potentia
179. ll any plant processes at all The crop is assumed to be active between the planting and harvest dates specified in the plant input file but in addition this function checks whether the crop simulation has been stopped by some other means in which case the growth stage is 6 Public Function is_transpiring This function returns True if and only if the crop object is transpiring i e actively growing in which case the simulation driver will call the crop s GetTransFrac function before partitioning potential GA PS Vorcinn 3 5 TTeor c Manual TER evapotranspiration into evaporation and transpiration In this model the crop is transpiring only during growth stages 1 through 4 Public Function has_matured This function returns True if and only if this grain crop has matured i e grain filling has stopped but grain drying is proceeding in which case the generic crop model s Daily_Growth_End procedure will simulate grain drying In this model this function is a direct translation of the matured growth stage Private Function heat_units This function is called by various of the daily growth processes to determine the daily heat units above some base temperature BaseTemp C It is based on the SORKAM function HFUNC The function is called with the base temperature and the daily mean MeanTemp both in C If the daily maximum temperature is less than the specified base there are no heat units If the da
180. major differences e The way in which demand is apportioned to the different soil layers EPIC does not translate unsatisfied demand downwards Instead of the explicit root density distribution used in the Plant available water uptake method the EPIC method uses an negative exponential distribution of roots with depth described by one parameter soil WUD which is an input parameter from the soil file Demand is approportioned to depth in a curve that ranges from linear for WUD approaching 0 from above to increasingly curved for increasing values of WUD The fraction of the total demand apportioned to the layers of soil from the surface down to the lower boundary ow_boundhayer 18 ade SEN x 1 UD x dow_bound low_bound AN ayer roots At the surface this function is 0 and at the lower boundary of the rooting zone it is 1 WUD controls the curvature higher values of WUD imply that more of the demand is apportioned to near surface layers In this EPIC model unmet demand is not transferred downwards so that a high WUD models the situation where dry surface soils can not be compensated for by moist subsoils Here is a MathCAD worksheet showing the curve for some typical values of WUD GA PS Vorcinn 3 5 TTeor c Manual 191 EPIC water uptake parameter WUD rooting depth 100 Depth of the deepest roots depth 0 rooting depth Depths at which to evaluate the function Cumulative proportion of total demand satisfied
181. may be selected by the GAPS user This allows the different crop models e g SORKAM and Stockle Riha to be compared with the same atmospheric soil and water uptake models e individual leaf development is not modelled instead we replaced this part of SORKAM with a model of composite LAI development e tillering is not modelled e the code is structured so that this crop model is a descendent object type of the generic GAPS crop model object type Rosenthal er al 1989 describe the objective of SORKAM as follows The simulation model SORKAM describes the morphological development of a well fertilized single grain sorghum plant in response to the environment Growth and development are assumed to be unaffected by insects and diseases SORKAM is intended as a guide for further research to evaluate growth and development of grain sorghum Since the GAPS implementation of SORKAM does not predict individual leaf development its use by crop physiologists may be limited However the GAPS implementation does predict growth stages photosynthesis stress dry matter and grain yield Throughout this description we refer to the original SORKAM documentation in particular to their subroutine names like LEAF and equation numbers like 53 Constructor Init This procedure is called whenever an object of type SK_model is created at run time Its purpose is to initialize the state of the crop model for example setting the current
182. me Date Time PTran ATran Drain WCC mm day LA UD Es UU A OO OO OO OO OO OC OO OC CH C GAPS3 EXAMPLE SUM 5 24 1994 10 42 59 UNPOONNDOONJSOOOOOOOO0O000000 a HRA b GA UI e OO OO OO OO OO OO CO OCH CH OO vn JO w J On OO Oe OO CO OC OC CH o N OOOO O O OO e Mr OLD O OO 0 60W 0 0 0 C GAPS3 EXAMPLE LAY 5 24 1994 10 43 8 GA PS Vorcinn 3 5 TTeor c Manual ISR 0 0 6 0 0 245 0 1 0 0 0 242 SO AR DD 24 1 6 4 5 0 0 246 0 0 0 0 0 240 0 0 0 0 0 240 0 0 0 0 0 240 1 1 0 1 8 243 D 0 0 0 0 240 A 5 6 0 0 240 0 0 6 2 5 240 0 4 3 6 6 244 0 0 0 0 0 240 0 0 8 5 1 241 1 0 7 0 0 238 Du 0 To 060 238 0 0 8 0 4 230 0 4 0 0 0 211 e EA E81 0 6 4 0 0 184 0 2319 050 219 0 3 1 0 0 176 0 4 6 0 0 154 0 3 2 0 0 170 0 2 1 0 0 175 8 9 10 sumDrain Sumwcchange SumWI ProfileWater ProfileAvail NetHeatFlux 131 129 128 132 126 26 26 30 26 27 26 30 126 SCH 125 24 17 98 68 71 05 63 40 56 61 11 13 14 15 16 17 W m2 kg m2 0 0 50 0 0 01 0 01 0 0 59 1 0 01 0 01 0 0 68 9 0 01 0 01 0 0 67 3 0 01 0 01 0 0 81 1 0 01 0 01 0 0 106 4 0 01 0 01 0 0 108 1 0 01 0 01 0 0 119 2 0 01 0 01 0 0 177 9 0 01 0 01 0 0 195 0 0 01 0 01 0 0 186 6 0 01 0 01 0 0 102 2 0 01 0 01 DOS 13290004 0 01 0 01 0 0 237 7 0 01 0 01 6 0 291 9 0 01 0 01 0 0 268 7 0 02 0 02 DD 214 9 0 03 0 03 0 0 363 1 0 09 0 07 0 0 181 5 0 22 0 17 0 0 202 4 0
183. me that file will be overwritten Printer Setup pops up a dialog box with a list of all the printers described in the gaps prt file The default is TEXT FILE which allows printing to text files instead of a printer Highlight a printer and select Ok to select it The number of the selected printer is saved in the Gaps configuration file gaps cfg Print pops up a submenu with all the filetypes that can be printed After selection of a filetype the Print file dialog box appears with the filename filter set to the selected filetype eg cli for climate files Move around and select the file you want to print DOS shell leaves GAPS temporarily to enter commands at the DOS command line To return to GAPS type EXIT at the command line and press Enter This option may not work when in real mode GA PS Vorcinn 3 5 TTeor c Manual AN Exit exits GAPS and returns you to the DOS command line 3 3 2 Edit The Edit menu lets you cut copy and paste text in windows You can also open the Clipboard window to view or edit its content To select text press Shift while pressing any arrow key The selected text will be highlighted To select text with a mouse drag the mouse pointer over the desired text To select a whole line double click anywhere in the line To extend or reduce the selection Shift click anywhere in the document Undo takes back the last editing command Cut removes the selected te
184. med to be negligable air temperature vapor density and windspeed must be known The Penman Monteith equation may be applied to both soil and cropped surfaces First we consider the computation of variables that are needed to predict evapotranspiration from either soil surfaces or crop canopies These are found in procedure Penman_ETP The saturation vapor density SVD g m 3 and the slope of the saturation vapor density function SSVD kg m 3 K 1 are calculated as a function of air temperature as described in the Priestly Taylor method above The actual vapor density VD g m 3 is updated on a daily basis using one of three methods in the following order of preference First if there is a measured value of vapor density for the day GA PS Vorcinn 3 5 TTeor c Manual 20 clim VaporDens real_day in the climate file this is used If not but if there is a measured value of relative humidity for the day clim RelHumid real_day in the climate file which should be the value of relative humidity at the maximum temperature VD is calculated multiplying the daily relative humidity by the saturated vapor density at the daily maximum temperature VD clim RelHumid real_day SVD clim MaxTemp real_day 1 If neither of these values are known we assume that the minimum daily air temperature is usually dew point temperature and calculate VD using equation 6 in section 6 3 1 1 To apply the Penman Monteith equation to a soil su
185. mount of water stored in the plant then we obtain the following way of calculating sim ActTrans the actual transpiration i e the water uptake by the plant under steady state in the plant in kg m sl emo sim RootWP sim WP NodeDepth GR sim ActTrans 1 Res i plant FRoot where plant FRoot and sim LRoot are the first and last soil layers containing roots sim RootWP I is the root water potential at anode J kg sim WP I is the soil water matric potential at the same node J kg I NodeDepth I is the depth of node J from the soil surface m GR is the acceleration of gravity downwards 9 8 m 72 and Res I is the root and soil resistance of layer J which is considered to surround node kg s m When we begin this procedure at each time step soil water potentials with depth WP 7 and the potential transpiration rate sim PotTrans are known If we can compute the resistances to water flow with depth we can then calculate a single root water potential that will result in the sum of water flowing from soil to roots at each soil depth exactly equal to the potential transpiration Consequently this procedure is broken down into two main parts which are called in sequence RootWaterPotential determine the root water potential e RootWaterUptake determine the water taken up from each layer knowing the root water potential However this whole process is bypassed if on entry to the procedure it is det
186. move to a new growth stage Then the current day s water stress index accumulated during the day inthe Critical Leaf Water Potential orSimple Water Stress procedures is added into the current growth stage s cumulative stress index these will be used to determine grain numbers at flowering If the crop has emerged but not yet matured private procedure Dry Matter Accumulation is called to simulate the conversion of photosynthate into dry matter This is simulated by calling private procedure Yield Finally the Daily_Growth_End of the generic Stockle Riha model is called to accumulate a stress index Public Function GetTransFrac The proportion of light intercepted for this crop as a monoculture is computed according to Stockle 1985 as GetTransFrac 1 exp 0 823 LAI 0 0286 LAL 1 where LAI m leaf m ground is the leaf area index of the growing maize crop Public Function PSTempFac This procedure computes a correction factor for the effects of air temperature on photosynthetic rate of maize It assumes that the leaf temperature LeafTemp C equals air temperature argument AirTemp and uses an equation from Stockle and Campbell 1985 derived from data of Hofstra and Hesketh 1969 PSTempFac 1 37893 0 184573 LeafTemp 7 6341E 03 LeafTemp 1 98485E 04 LeafTemp gt 2 15152E 06 LeafTemp 1 Private Function Growth_Stages This function is called at the end of each day and it returns the curr
187. mulas to estimate runoff from daily precipitation the current water content of the soil the site slope and the runoff curve number developed by the USDA Soil Conservation Service SCS 1972 The advantage of this method is that it uses readily available data daily rainfall and the curve number This latter summarizes the runoff characteristics of the site with respect to soil type land use and management Curve numbers range from 0 no risk of runoff to 100 extreme risk of runoff Runoff curves are easily obtained for all USA soils from the EPIC data set or SCS hydrology tables which take into account the soil s hydrologic group based on infiltration rate hydrologic condition e g surface sealing land use and management practices For example fallow on soils in group D results in a curve number of 94 close seeded legumes on contoured and terraced soils in group A in good hydrologic condition results in a curve number of 51 The basic idea of the curve number method is to estimate runoff from the daily rainfall and a retention parameter which is adjusted according to the soil water content The equation used to calculate runoff is Runoff Precip 0 2 s 2 Precip 0 8s if Precip gt 0 2 s Runoff 0 if Precip lt 0 2 s 1 where Runoff is the daily runoff Precip is the daily precipitation and s is the retention parameter all expressed in kg m i e mm of water The value 0 2 s is a threshold so that if the
188. n comes together with the Borland Pascal compiler Some bugs in Turbo Vision had to be fixed An un official list of bugs in Turbo Vision 2 0 is put together by Brad Williams and can be downloaded via ftp at vtucs cc vt edu in the turbo vision faq directory as TVBUGSx ZIP Except for the Turbo Vision framework the complete source code for GAPS is provided A simple flowchart is given in appendix D The compiler settings memory sizes and directory settings used to compile the executables is given at the beginning of the files gaps pas gsb pas and readme pas 6 1 Changing GAPS limits In a practical computer program it is necessary to place limits on the size of data structures In GAPS these are as follows Variable names in source file global pas are given in parentheses and the approximate additional memory in bytes needed for each increment in brackets 1 the maximum number of time steps in a day MaxTimeStep fixed at 24 12 i e every 5 minutes penalty 0 2 the maximum number of years that can be simulated in one run MaxYears fixed at 11 penalty 70 3 the highest numbered soil layer MaxLayer fixed at 20 This is one greater than the number of soil layers since layer 1 represents the atmosphere so that the maximum number of soil layers is 19 penalty 128 static up to 48 dynamic depending on procedures selected at run time 4 the maximum number of crops that can be simulated MaxCrops fixed at 6 penal
189. nce error is less than a pre defined limit of 10 6 kg m2 el Non convergence is detected by counting the number of iterations and halting the simulation if a pre defined limit of 256 is exceeded Conductivities are calculated by sim KJayer soil HydCondjayer MFPJayer AirEntryMFPiayer P gt layer 3 where the exponent B3 is derived from the slope of the moisture release curve by B3layer 2 soil BValuejayer 3 soil BValuejayer 3 4 Soil evaporation is computed exactly as in the Richards Equation method The mass balance equations are set up similarly but the difference in matric flux potential approach are the gradients The Thomas Algorithm is the same but the values obtained by the back substitution are the new matric flux potentials not the water potentials If any matric flux potential becomes too negative it is set to a small positive potential 0 000001 J ke The the new water contents sim WN are computed from the new matric flux potentials MFP and the constant saturated water content WS and the matric flux potential at saturation AirEntryMFP by sim WNlayer WSlayer MFPlayer AirEntryMPP layer soil BValue 3 5 After the numerical solution converges we can compute the fluxes in subprocedure Calculate Fluxes from the final matric flux potentials sim WFlux I sim K I sim WP I sim K I 1 sim WP I 1 A N NodeDelta I GR sim K I 6 5 5 4 Workability and Traff
190. nction is the modified growing degree days based on Barger 1969 which constrains the maximum temperature to 30 C and the minimum to 10 C Private procedure Max_Photosynthesis Both sunlit and a shaded rates of photosynthesis PSSun and PSShade g m2 sl are then calculated assuming that photosynthesis is related to PAR according to an equation given for maize by Hesketh and Baker 1969 This rate is then modified for leaf temperature using a temperature factor TempFac which 1s obtained by calling the correct virtual procedure for the submodel The code TempFac PSTempFac AirTemp calls one of the virtual functions e g SRw_model PSTempFac for wheat which returns the temperature factor See the submodels for a description of the computation of the temperature correction factors This factor which depends on leaf temperature is further multiplied by another linear factor that does not vary with temperature TempCoeff This is crop specific and is set by the constructor of each Stockle Riha submodel For maize this is 6 2527E 05 0 7 and for wheat 1 6 2 23583E 05 So the product of the linear factors is on the order of 1 Another crop specific factor is TempPower which is the exponent to which PAR is raised This is set by the constructor of each Stockle Riha submodel For maize this is 0 507578 and for wheat 0 695407 Given these factors PAR is converted to PS by these equations GA PS Vorcinn 3 5 TTeor c Manual
191. ndSpeed is not known SR_model Critical_Leaf Water Potential Penman _ ETP Penman ETP when crop is growing cf loca AS Plant record variables are local to the general crop model and are loaded when the new crop is initialized Data field Variable name Units of Modules in which field is used measure Initial Leaf Area m2 m2 crop_model constructor ee Index for SK_model Default 0 07 dra matter accumulation daily_plant_growth SR model Growth_Stages Max_Photosynthesis model GetTransFrac Note inital LAI gt 0 07 Initial dry matter InitialDryMatter kg ha crop_model constructor initializes for SR_model Default 0 Dry_Matter_Accumulation SK_model dry_matter_accumulation Maximum rooting MaxRooting m SK_model daily _plant_growth depth Depth SR_model Default 1 20 Dry_Matter_Accumulation note for water uptake roots are considered to exploit the entire layer in which MaxRootingDepth occurs Sowing depth SowingDepth m SR_model Dry _Matter_Accumulation Default 0 025 SK model emergence daily_plant growth GA PS Vorcinn 3 5 TTeor c Manual 21 All the following variables are local to specific crop models Stockle Riha crop model specific variables Data field Variable name Units of Modules in which field is used measure Maximum water plant Canopy Max kg m2 leaf on canopy Default 2 Critical leaf water plant Critical J Kg Critical_Leaf Water Potential potential Lea
192. ndingly less heat units from 6 27 C and 33 43 C and no heat units i e effectively no plant development above and below this range The daily heat units are added into the accumulated heat units since emergence AccDD Then the accumulated heat units are compared to the number of units necessary to move to the next growth stage which of course is dependent on the current growth stage These transition heat units are stored in the constant array AccDD_to growth_stage These are the crop coefficients of the plant data input file and are read in when the crop is initialized in the constructor AN model Init However the transition from growth stage senescing to mature is not based on heat units since the plant is not actively growing instead this transition is effected when the simulated LAI drops below 0 01 LAI is adjusted in private procedure Dry Matter Accumulation In addition even if the plant is not yet in the senescing stage but is past the vegetative stage it will be forced to maturity if the LAI has dropped below 0 01 because of water stress If the growth stage is past emergence but before senescence the number of days since emergence is incremented This number of days is used in the piecewise dry matter partitioning function in Dry Matter Accumulation Finally the standard base 10 C growing degree days is computed This is not used in the simulation but may be shown on a graph The actual fu
193. nes starting with the Comments added after the input data 1 integer plant file The plant file must be saved with the extension EN s70 string 70 SPER sign are ignored at input preceded by a are also ignored crop options loaded in croplib load crop option crop options 1 amp 1 Stockle Riha maize 0 proc _status 1 gt Canopy water interception 0 proc _status 2 gt Critical leaf water potential 0 proc _status 3 gt 0 proc _status 4 gt 0 proc _status 5 gt 0 proc _status 6 gt 0 proc_status 7 gt 0 proc_status 8 gt 0 proc_status 9 gt loaded in croplib crop_model init corn late crop PlantName s70 123 crop SowingDate i d 296 crop HarvestDate i a 1500 crop RootWP s J kg 0 0020 crop RootRad s m 2 5E 0010 crop RootRes s m4 kg s 3 crop FRoot i 0 crop NRoot i 50000 00 crop RootDens 3 s m m3 for n FRoot to NRoot 40000 00 crop RootDens 4 s m m3 for n FRoot to NRoot 27000 00 crop RootDens 5 s m m3 for n FRoot to NRoot 8000 00 crop RootDens 6 s m m3 for n FRoot to NRoot 3000 00 crop RootDens 7 s m m3 for n FRoot to NRoot 6700 00 crop RootDens 8 s m m3 for n FRoot to NRoot 2300 00 crop RootDens 9 s m m3 for n FRoot to NRoot 690 00 crop RootDens 10 s m m3 for n FRoot to NRoot 50 crop CanopyHeight s m
194. ng a water potential y 100cm 9 8 MJ kel 0 Imbar for the upper limit and y 15 000cm 147 15 MJ kel 5mbar for the lower limit These values can also be estimated from soil textural data and organic carbon content using empirical equations contained in CERES Maize Ritchie et al 1986 and later work along the same line e g Ritchie amp Crumb 1988 The Tipping Bucket water flow method is well matched with the Plant available water uptake method both conceptualizing the soil layers as compartments which have a volumetric water capacity At the beginning of the simulation the procedure Tipping Bucket Init is called to determine time invariant coefficients for the module including evaporation and drainage coefficients At each time step the procedure Tipping Bucket is called to compute the soil water balance This procedure is broken down into a series of sub procedures e Null Setting initialize inter layer fluxes and drainage rate to zero e Infiltration model the downward flow of water from bucket to bucket Soil Evaporation evaporate from the soil surface Calculate Fluxes record the new water contents These sub procedures as well as the main control procedure are now discussed in detail 5 5 2 1 Procedure Tipping_Bucket_Init This procedure is called at the beginning of the simulation to estimate time invariant coefficients used in the dynamic simulation These deal with inte
195. nopyWater kg m2 ground then we assume that all the water on the canopy is evaporated and that potential transpiration is reduced by this GA PS Vorcinn 3 5 TTeor c Manual AR amount due to the energy needed to evaporate the water Otherwise the potential transpiration rate is set equal to zero and canopy water reduced by the amount evaporated Private procedure Light_Interception In procedure Light Interception the sunlit and shadelit leaf areas are calculated and direct and diffuse photosynthetically active radiation PAR interception is summed It is only called in the daytime i e when the solar elevation angle is positive At night photosynthesis is assumed to be zero and the stomatal resistance is set at a high value representative of closed stomates 3200 s m This procedure begins by determining the amount of leaf area that is sunlit An extinction coefficient X for a spherical random leaf angle distribution is calculated as a function of the sine of the solar elevation angle SSo EIA as follows K 0 5 SSolEIA 1 This equation as well as others for calculating extinction coefficients for different types of leaf inclination angles is presented and discussed in Campbell 1977 The sunlit leaf area index LA Sun is then calculated as a function of the total leaf area and extinction coefficient LAISun 1 EXP K LAD K 2 where LAJ is the leaf area index m2 leaves m 2 ground and K is the can
196. ns the Open File dialog appears prompting for the def file The different directories are listed To move to a subdirectory double click on the directory name or highlight the name of the directory and select Open To move a directory up towards the root select the directory After selection of a def file climate def location def soil def save def pconst def pcorn def plant def psorkam def pepic def ptree def or pwheat def a new file Untitled will be created with the content of the selected def file You can put your own comments in the def file so that all the new files you create will contain those comments To save the new file under a filename with the appropriate extension cli sol loc plt or sav while in the Save file as dialog move to the directory where you want to save the file enter the new name and select Ok The current directory is displayed at the bottom of the Save file as dialog Open pops up a submenu with the 6 different types of input files and the 6 types of output files After selection of a filetype the Open file dialog appears prompting for the file to open For selection and moving around in the Open file dialog see New Save saves the file of the current active window to disk Save as allows you to save the file of the current active window under a different name Enter the new name optionally with drive and directory and click or choose Ok If you pick an existing filena
197. nt of F for reduction of 1 0 0 8 1 2 photosynthetic rate 1 after Stockle 1983 2 Monteith 1981 3 during early vegetative phase 4 during late vegetative phase A key concept of this model is the growth stage The plant is considered to be in one of a set of mutually exclusive stages from planting through harvest The stages control or modify various behaviors of the plant e g the rate of dry matter production The stages are listed in the enumeration data types SRm_GrowthStages and are pre emergence vegetative pollination late lag early grain filling senescing i e late grain filling and mature The plant moves from stage to stage according to accumulated heat units and days as explained in private function Growth_Stages Constructor Init This procedure is called by the simulation driver whenever an object of type SRm_model is created at run time Its purpose is to initialize the state of the crop model Destructor Done This procedure is called by the simulation driver whenever an object of type SRm_model is destroyed at run time Its only purpose is to deallocate the heap space used by the object GA PS Vorcinn 3 5 TTeor c Manual Sd Public procedure Daily_Growth_End This procedure is called by the simulation driver at the end of each day It first accumulates a stress factor which is used to limit LAI It then calls private function Growth Stages to accumulate degree days and possibly
198. o file requires about 2 5 Kb on disk GA PS Vorcinn 3 5 TTeor c Manual Ed 4 Running GSB Program gsb exe is a stripped down version of GAPS with the same simulation procedures as the interactive version but a non iteractive command line user interface intended for batch processing This will be of interest to you if you need to run large numbers of simulations with only slightly changed parameters For example we used this program in a project to investigate the effects of climate change on US agriculture using a large number of synthetic climates You run program gsb exe from the DOS command line Without any parameters it will show the correct usage as follows Batch simulation gsb lt scenario file name gt lt filetype gt lt sequence gt lt filename gt Scenario file names have the default extension set Valid filetypes and their default extensions are c climate cli p plant PLE s soil Sol 1 loca Loc x Save Sav q sequence seq 0 output sum and det can t be overridden Code c may optionally be followed by a sequence number For example c 2 second year s climate c by itself is equivalent to c 1 For multiple plants use a cropping sequence file As this shows GSB must be run with at least one parameter the name of a simulation scenario file GAPS set file The scenario file contains the names of the input an
199. ocedures Begin growth Daily Growth Begin Daily Growth End TimeStep Growth End Growth open det file write summary public functions GetTransFrac is active is transpiring has matured private procedures Water Interception This model simulates a constant crop that grows immediately to final dimensions From planting to harvest the crop is active transpiring and mature and has a constant height rooting depth LAI and biomass It is useful to simulate situations with a more or less steady state vegetative cover and also to examine the non dynamic effects of competition on another crop model Constructor Init This procedure is called whenever an object of type SC_model is created at run time Its purpose is to initialize the state of the crop model Destructor Done This procedure is called whenever an object of type SC_model is destroyed at run time Its only purpose is to deallocate the heap space used by the object Public procedure Begin_Growth This procedure is called at the beginning of crop growth It computes several parameters that do not vary during the course of the simulation including e the accumulated total dry matter AccTotalDryMatter which is set to the maximum value of Plant_MaxTopDM and plant InitialDryMatter e the accumulated top dry matter AccTopDryMatter Plant_MaxTopDM e the accumulated root dry matter AccRootDryMatter AccTotalDryMatter AccTopDryMatter e the ro
200. odel Model options gt Yield Acc degree days from emergence to maturity 62 14 summary water budget kg m2 or mm Total Precipitation 586 AccPrecip Total Runoff A 0 AccRunoff Total Water Input to Surface S 586 AccWI Total Potential ET 1319 AccETP Total Potential Transpiration 420 AccPotTrans Total Actual Transpiration S 296 AccActTrans Total Potential Evaporation E 899 AccPotEva Total Actual Soil Evaporation x 262 AccActEva Accumulated Deep Drainage 64 AccDrain nitially in profile 245 InitialWater Finally in profile 184 FinalWater Change in Storage 61 FinalWater InitialWater KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK Ending simulation on 5 24 1994 at 10 40 49 Daily summary example sum BSS oo w o 40 LA ANAN OCON Gs vs vs A AA kA OO OO CH GAPS Vorcinn 2 5 Tleer s Manual TINA O 64 0 64 0 64 0 00 0 00 0 00 0 64 0 00 245 31 0 00 50 01 0 010 0 010 98 0 98 0 98 0 00 0 00 0 00 0 98 0 00 242 29 0 00 59 12 0 010 0 010 81 0 81 0 81 0 00 0 00 0 00 0 81 0 00 241 28 0 00 68 94 0 010 0 010 86 0 86 0 86 0 00 0 00 3 62 4 48 0 00 246 32 0 00 67 33 0 010 0 010 24 1 24 0 00 0 00 0 00 0 00 0 00 0 00 240 26 0 00 81 05 0 010 0 010 68 1 68 0 00 0 00 0 00 0 00 0 00 0 00 240 26 0 00 106 38 0 010 0 010 32 1 32 0 00 0 00 0 00 0 00 0 00 0 00 240 26 0 00 108 07 0 010 0 010 67 2 67 2 67 0 00 0 00 0 12 1 04 1 75 243 30 0 00 119 23 0 010 0 010 10 4 10 0 00 0 00 0 00 0 00 0 00 0 00
201. odel The first is intended to be matched with the Richard s Equation or Matric Flux Potential soil water flow models since these consider water from the point of view of its potential energy in J kg of water The second is intended to be matched with the Tipping Bucket soil water flow model since these GA PS Vorcinn 3 5 TTeor c Manual 115 consider water from the point of view of its volumetric content in soil layers The third matches the model described by Williams J R Jones C A and Dyke P T 1989 as part of EPIC An interesting point is that these procedures do not actually remove water from the soil profile i e the water content sim WN is not affected That step occurs during the water flow procedures using the per layer water uptake sim WUptake calculated here 5 7 1 Potential driven water uptake source file soillib pas procedures WaterUptake Init WaterUptake WaterUptake Done In this method the amount of water flowing from soil to roots is considered to be directly dependent on how much more negative the root water potential RootWP is compared to the soil water potential sim WP in a layer Gardner 1960 Water flow into roots has also been considered inversely dependent on the resistance to water flow in the soil and in the root Gardner and Ehlig 1962 If we combine these two concepts with the assumption that there is steady state water flow through the plant i e there is no change in the a
202. of a series of buckets each having a specified capacity to hold water Each bucket corresponds to a soil layer the dimensions and properties of which are specified in the soil input data file Water is transferred from one layer to the next downward in the soil profile if the amount entering the layer exceeds the layer s water holding capacity This is analogous to tipping a bucket thereby letting some water spill out of it to the one below The capacity of each soil layer to hold water is calculated as the difference between the saturation water content WS and the current volumetric water content sim WN both expressed as m3 m3 This method is not iterative the capacities at the beginning of the time step are used to estimate the redistribution of water during that time step Also in this method water can not move upwards between layers although water can evaporate from the upper layers Input requirements for this procedure include values for bulk density and particle density to calculate saturation water content field capacity or Drained Upper Limit DUL and wilting point or Lower Limit volumetric water contents LL Ideally values for DUL and LL should be obtained from field measurements as described by Jones and Kiniry 1986 They can be estimated using the method presented in the Workability and Trafficability section of this manual using equation 1 of that section and its associated tables usi
203. of potential evapotranspiration sim ETP into potential transpiration sim PotTrans and potential soil evaporation sim PotEva according to the fraction of solar radiation intercepted by the canopy This procedure first obtains TransFrac the fraction of light absorbed by the total canopy by a call to the competition model TransFrac TheCompModel GetTransFrac GA PS Vorcinn 3 5 TTeor c Manual 4 See the description of the competition module for the computation of this transmission fraction Using this transpiration fraction TransFrac the simulated rate of ETP is partitioned as follows sim PotTrans sim ETP TransFrac 1 sim PotEva sim ETP 1 0 TransFrac 2 or equivalently sim PotEva sim ETP sim PotTrans 2 The potential transpiration is further divided by the competition module into the potential transpiration of each active crop model GA PS Vorcinn 3 5 TTeor c Manual 43 5 4 Plant processes The crop models in GAPS are arranged in a hierarchy using the inheritance feature of the object oriented language Turbo Pascal 7 0 There is a generic crop model crop_model which defines the fundamental structure of all GAPS crop models but which does not itself implement a complete crop model and can not be selected by the GAPS user Descended from this are four main crop models Stockle Riha based on the work of Stockle amp Campbell 1985 and adapted by I Buttler and S Riha maize D Rossite
204. of these private procedures below Public procedure TimeStep_Growth This is called at each simulated time step Although SORKAM only changes the plant s state once a day other GAPS procedures in particular the plant water uptake procedures operate on a less than daily time step Both water uptake methods are based on the time step s simulated potential transpiration which is first calculated by the atmospheric procedure Partition ETP and then modified by the crop model to account for water stress that reduces transpiration This procedure simply reduces simulated potential transpiration by a fraction sim PotTrans sim PotTrans Watco 1 where Watco is a fraction which is computed for just this purpose in the private function SK_model_water_stress each day see below Public Function GetTransFrac The proportion of light intercepted for this crop as a monoculture is computed according to SORKAM equation 51 as GetTransFrac 0 53 LAI9 5 where LAI m2 leaf m ground is the leaf area index of the growing crop This is gt 1 for LAI gt 3 56 which is impossible therefore the result is limited to 1 0 If LAI gt 1 0 53 0 53 then GetTransFrac 1 SORKAM is unusual in that it doesn t estimate the fraction with a negative exponential function of increasing LAL Public Function is_active This function returns True if and only if the crop object is active i e if the simulation driver should ca
205. of wind Boundary layer Default 24 WindHeight m speed measurement Default 2 GA PS Vorcinn 3 5 TTeor c Manual dimension less Default 1 26 dimension less Default 1 0 dimension less Default 1 0 W m2 K Default 20 0 SolarAngle Linacre ETP SK_model emergence for tropical cultivars only SolarAngle Priestly_Taylor_ETP Pan_ETP Pan_ETP Soil_ Temperature Distribute_Precipitation Distribute_Precipitation Penman_ETP Elevation Depth to which soil must be dry in order to till to traffic Water content at which soil must be below in order to till to traffic Water potential at which soil must be below in order to till to traffic Maximum depth to which evaporation can dry soil to less than the DUL CO concentration of the atmosphere Elevation WorkMaxDepth till WorkMaxDepth traffic WorkLimitWN till WorkLimitWN traffic WorkLimitWP till WorkLimitWP traffic depth_of evap CO2ext m above mean sea level Default 0 m Defaults 0 15 0 05 Defaults 0 37 J kg Defaults 9 8 m Default 0 05 g m Default 0 54 Linacre_ETP Is_workable Is_workable if water flow method is Tipping_Bucket Is_workable if water flow method is Richards Equation or Matric_Flux_Potential Tipping_Bucket SR_maize_model Critical_Leaf Water Potential In the computer code all location parameters are in
206. omputed as WUptake TheCrop crop_i PotTrans 1 e soil WUD 1 e soil WUD soil LowBound 1 soil LowBound TheCrop crop_i LRoot aboveUptake 2 GA PS Vorcinn 3 4 Tleor s Manual 122 where TheCrop crop_i PotTrans is the rate of transpirational demand kg m s for the crop soil WUD is the water use distribution parameter soil LowBound i the depth for the current layer and soil LowBound TheCrop crop_i LRoot the root zone depth for the crop The aboveUptake is the water use rate for all the layers above the current layer results from previous calculations as the procedure works downwards If the soil water storage is less than 25 of the plant available soil water if soil DUL i soil DLL i 4 soil DLL i gt sim WN i then then the potential water uptake calculated for the current layer is reduced with the factor exp 20 sim WN i soil DLL i soil DUL i soil DLL i 5 where sim WN i is the soil water content in layer i Thereafter if the estimate of water uptake exceeds the available water in the layer if WUptake time_step gt LayerAvail i then the water uptake is limited to the plant available water WUptake LayerAvail i time_step The crop s active transpiration is accumulated as well as the total uptake in the layer TheCrop crop_i ActTrans TheCrop crop_1 ActTrans WUptake sim WUptake layer sim WUptake layer WUptake The
207. ooooooooooocoooooooooooo 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000021 000023 000028 000126 000103 000186 000117 000091 000142 000101 000061 3 1500 1500 1500 1500 0000000 0002115 0000000 0000000 0000046 0000000 0000000 0000217 0000089 0000060 0000061 0000109 0000104 3 9 9090092209 9 4 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 CO OCH CO CO COOC COOC OO OO OO OO OO OO OCH 4 a GA PS Vorcinn 3 5 TTeor c Manual 0 0000000 0 0000000 0 0000000 0 0000000 0 0000000 0 0000000 0 0000207 0 0000207 0 0000006 0 0000227 0 0000227 0 0000000 0 0000278 0 0000278 0 0000000 0 0001255 0 0001255 0 0000000 0 0001027 0 0001027 0 0000000 0 0001860 0 0001860 0 0000000 0 0001609 0 0001170 0 0000000 0 0001251 0 0000910 0 0000000 0 0001421 0 0001421 0 0000000 0 0002007 0 0001010 0 0000000 0 0001207 0 0000607 0 0000000 5 6 7 7 Drain rate 8 Win H WC change 10 ProfileWater Dl ProfileAvail 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00 0 00 0 1 00 0 00 0 00
208. opy extinction coefficient computed according to equation 1 The shaded leaf area index LAIShade is computed as the difference between the total leaf and the sunlit leaf area LAIShade LAI LAISun 3 Following this photosynthetically active radiation PAR W m2 is calculated from the daily solar radiation assuming that half of the short wave spectrum is PAR PAR 0 5 DailyRad SpaRad 4 where DailyRad is today s proportion of theoretical solar radiation and was computed in the daily growth begin procedure as DailyRad TheCompModel MySolRad MyCropl MJd_to_W SpaceSum where the function MySolRad is the portion of clim SolRad measured daily solar radiation MJ m2 dl allocated to this crop by the competition module which is then converted to W m2 by multiplication with 11 574 1 86400 s dl 1000 and SpaceSum is the theoretical solar radiation for a given day W m2 Thus DailyRad is a proportion 0 1 of theoretical daily radiation Returning to equation 4 SpaRad is the theoretical solar radiation above the atmosphere during the time step W m2 so that when this is multiplied by DailyRad we have the radiation flux density to this crop during this time step W m GA PS Vorcinn 3 5 TTeor c Manual 40 This computed PAR W m2is then used to calculate direct and diffuse photosynthetically active radiation PARSun W m2 and PARShade W m2 by the method of Norman 1982 The direct PAR
209. or c Manual 15A soilFileName soil soilName soil SwAbs soil CN soil slope soil WUD soil LastLayer date time Water Content Initial Cl soil Temp Initial DUL DLL m3 m3 deg C 28 0 28 0 14 20 0 25 28 0 28 0 14 20 0 25 28 0 28 0 14 20 0 25 28 0 28 0 14 20 0 25 27 0 27 0 14 20 0 25 22 0 522 0 11 20 0 25 22 0 22 0 11 20 0 25 05 0 05 0 01 20 0 25 05 0 05 0 01 20 0 25 05 0 05 0 01 20 0 25 05 0 05 0 01 20 0 25 7 8 9 11 soil InitSoilTemp 12 soil Clay layer 13 soil Silt layer 14 soil Satwt 15 CoarseFrag NumberOfHours NumberOfDays Layer Lower Bulk Particle Saturated Air Entry B no Boundary Density Hydr Conductivity Potential Value m Mg m3 kg s m3 J kg 2 0 01 1 35 2 65 0 00300 0 30 7 80 3 0 05 135 2 65 0 00300 0 30 7 80 4 0 15 1 35 2 65 0 00300 0 30 7 80 5 0 30 1 35 2 65 0 00300 0 30 7 80 6 0 48 1442 2 65 0 00300 0 30 7 80 7 0 66 150 2 65 0 00300 sall SD 7 80 8 0 84 1 50 2 65 0 00300 0 30 7 80 9 1 00 1 55 2 65 0 00300 0 30 7 80 10 1 10 EN 2 65 0 00300 0 30 7 80 11 1 30 1255 2 65 0 00300 0 30 7 80 12 1 50 1 58 2 65 0 00300 0 30 7 80 1 2 3 4 5 6 1 layer 6 soil AirEntryPot layer 2 LowBound layer 7 soil BValue layer 3 soil bulkDensity layer 8 soil InitWater 4 soil PartDensity layer 9 soil DUL layer 5 soil HydCond layer 10 soil DLL layer Plant file printout id example plt Save file printout save txt GAPS Save Format File Data
210. or R as Z R 0 1 gt z 1 3x2 z In z 1 gt x2 In 1 1 5 For each layer we set x x2 i e the top boundary of the layer is the bottom boundary of the previous layer so the corresponding contribution to the definite integral in 3 are the same with a change of sign and we then calculate the new contribution to the definite integral in 3 by z R soil LowBound layer 1 6 x2 z In z 1 7 Here equation 6 expresses the change of variables 2 We now complete the computation of the definite integral 3 to obtain the evaporation fraction Integral x2 x1 R 8 and divide by the layer thickness to obtain an average evaporation fraction over the layer EvapFrac layer Integral LayThick layer 9 where LayThick is the layer thickness m so that EvapFrac is a fraction The procedure of equations 5 9 is followed for each layer until EvapFrac becomes greater than 1 i e the layer on average is too deep for evaporation to affect it or the bottom of the profile whichever comes first The final layer in which evaporation is effective is recorded in module variable EvapLastLayer which controls the evaporation loop in the time step procedure If the surface layer as specified in the soil input file is too thick even the first layer s fraction will be greater than 1 To allow evaporation in this special case we arbitrarily set the fraction to and evaporate only from thi
211. or tillage and about 5cm for traffic only n b this 5cm depth was used by Bouma amp van Lanen in the studies cited below Determination of the critical water potential should ideally be done with a field study of infiltration rate or penetrometer resistance versus water potential see e g Bouma amp van Lanen 1987 Such studies reveal a critical or threshold water potential which corresponds to a penetrometer resistance of approximately 50 KPa In studies reported by Bouma and van Lanen this resistance corresponded to a pressure head of 90 cm water for a heavy clay and to 40 cm for a sand In GAPS potentials are always expressed as MJ kel the conversion between the units is based on the acceleration due to gravity 9 8m s 2 so that to obtain potentials in MJ kg for GAPS one multiplies the pressure head expressed in cm by 0 098 For example 90 cm of water is equivalent to 8 82 MJ kel If the Tipping Bucket water flow model is used the critical water potential must be converted to an equivalent critical volumetric water content m m Ideally this relation should be determined experimentally A set of soil moisture vs pressure head relations has been collected in the Netherlands van Keulen amp Wolf 1986 p 81 and an equation has been developed which allows prediction of water content SMy from the suction head yy SMy SM e Un Y 2 1 where y is expressed in cm of water i e MJ kg x 10 20 and SMy is fr
212. ost always gives the best results and will be used hereafter Other sources sinks not represented in 6 such as root extraction gravitational flux precipitation or irrigation are added explicitly to the mass balance term in 7 and such become part of the solution Root extraction i e sim WUptake is added as a sink to each layer Evaporation is assumed to be only from the surface so sim ActEva is added as a sink to the top soil layer only Water input from precipitation or irrigation sim WInput MinLayer is assumed to be only at the surface so this term is added as a source to the top soil layer only GAPS at present can not simulate ground water tables or lateral fluxes from soil layers this could be done by calculating source or sink terms WInput for the lower layers Equation 7 can be written for each node in the simulated soil profile resulting in LastLayer equations in LastLayer 2 unknowns Boundary conditions are used to reduce the number of unknowns by two so that the system of equations can be solved simultaneously The three choices for boundary conditions are 1 measured values 2 assumed constant flux and 3 assumed constant potential For the profile s upper boundary the soil water potential can be set to the air entry potential during infiltration in order to simulate saturation or to a specified flux density in the case where the water input is less than the infiltration rate At the bottom of the profile the poten
213. oting depth RootingDepth plant MaxRootingDepth e and the leaf area index LAI plant LAI or minimum 0 07 Public procedure Daily_Growth_End This is called at the end of each simulated day The growing degrees days is calculated as GDD Tmax Tmin 2 plant BaseTemp and GDD gt 0 The growing degrees days are accumulated into AccDD GA PS Vorcinn 3 5 TTeor c Manual Ra Public procedure TimeStep_Growth This is called at each simulated time step This procedure calls the Water Interception procedure if Canopy Water Interception proc_status 1 in the plant input file was checked Public Function GetTransFrac The proportion of light intercepted for this crop as a monoculture is computed as GetTransFrac 1 exp plant_ExtinctionCoeff LAD where LAI m2 leaf m ground is the leaf area index of the growing crop Public Function is_active This function returns True between the planting and harvest dates specified in the plant input file Public Function is_transpiring This function returns True between the planting and harvest dates specified in the plant input file Public Function has_matured This function returns True between the planting and harvest dates specified in the plant input file Private Procedure Water_Interception This procedure is identical to the Water_Interception procedure called in the Stockle Riha model 5 4 5 Crop model EPIC model source file epic pas object name SE model
214. out The solution is to limit the depth to which the soil must be dry enough to the depth to which evaporation is effective Thus GAPS automatically adjusts the depth to which the soil must be workable to the evaporation depth ifthe Tipping Bucket water flow method has been selected GAPS vs reality When calibrating GAPS predicted field hours against observed field hours e g experiment station records it is necessary to determine what kind of field operations could be performed and set up the parameters depth moisture status to correspond with this For example tillage hours are usually less than traffic hours for such purposes as sidedressing with hours for planting in between It may be necessary to simulate field hours for several classes of field operations and then combine them according to the mix of operations in a time period 5 7 Runoff Some of the precipitation that reaches the soil surface does not infiltrate into the soil but instead runs off the site Without taking runoff into account the simulated soil may be wetter than the actual soil GAPS provides only one way to estimate runoff 5 6 1 Curve number EPIC runoff source file rainlib pas procedures Runoff_CN Init Runoff_CN Daily Runoff_CN Done access functions Runoff_CN GetThreshold This method of estimating runoff closely follows the method which forms part of EPIC Williams et al 1989 It operates on a daily time step using empirical for
215. ow is assumed to be unsaturated First the layer s new water content is calculated by sim WN I W I Flux I sim WUptake I time_step KgFines T 3 where the current water content W replaces the saturation water content WS of equation 3 and there is no saturated flow the Drain term in 3 This new water content will be less than the saturated water content If this new water content is not above field capacity i e sim WN I lt soil DUL then the infiltration process is stopped by setting the flux out of this layer Flux 1 to zero Otherwise some water is assumed to drain out of this layer to the next and the sub procedure UnSaturated_Flow is called to calculate this flux out of the layer and re adjusted the water content as follows This sub procedure first determines the amount which can drain from the layer during the time step Drain kg m2 as Drain Profile SWCON sim WN I DUL I KgFines I 5 where sim WN I DUL I is the volume of water presently contained in this layer above field capacity and Profile SWCON controls the speed of drainage as explained above for equation 2 This amount is then moved out of the layer by recomputing the layer water content and the flux into the next layer sim WN I sim WN I Drain 6 Flux I Drain KgFines I 7 At the end of this subprocedure Flux I is the amount of water moving out of this layer Procedure Soil_ E
216. perature and potential evapotranspiration but before the plant water uptake and soil water flow Thus the model has a current estimate of potential ETP but only the previous time step s estimates of root water potentials In the generic crop model this procedure does nothing Itis a placeholder for the procedure of the same name in descendent crop model object types Public procedure Daily_Growth_End This procedure is called by the simulation driver at the end of each day after the descendent crop model has finished simulating daily growth It accumulates the total dry matter and if there is any grain accumulated on a matured grain crop calls a procedure to simulate grain drying Public procedure End_Growth This procedure is called by the simulation driver at the end of crop growth i e at harvest or the end of the simulation It logs this fact to the simulation summary file and resets some state variables for the run time graphs Public Function GetTransFrac The proportion of light intercepted by the canopy for this crop as a monoculture is computed as a simple function of the leaf area index GetTransFrac 1 exp 0 5 LAT 1 where LAI m2 leaf m ground is the leaf area index of the growing crop Note that when LAI 0 i e there is no crop GetTransFrac is 0 1 e all light reaches the ground as LAI increases GetTransFrac increases exponentially towards 1 Public Function is_active This function returns
217. pirical relations to be evaluated outside their calibrated ranges Error 206 Invalid numeric format in Read This is most likely called by an incorrect input data file If you prepare your data files using correct formats you should not get this error if you do it s a programming error See the read statements in the appropriate load_ procedure in source file fileio pas for the formats of each data item Error 256 Non convergence of iterative solution See the section on the soils input file 3 4 1 2 above for a discussion of how soil files can be changed to avoid this error Error 259 Couldn t balance carbon The Stockle Riha wheat model uses an iterative Newton Raphson root finding method to determine the daily partitioning of available C to roots shoot grain and reserve If this doesn t converge error 259 is generated GA PS Vorcinn 3 5 TTeor c Manual 124 Appendix C Input and output files An example is given for most input and output files Comments are printed in italic Def files Climate file climate def GAPS 3 0 climate file with the default values The climate file must be saved with the extension CLI Lines starting with the sign are ignored at input Comments added after the input data preceded by a are also ignored s single 1 integer b boolean s70 string 70 NO NAME ClimateName s70 FirstDay i day of year 365
218. plitude SurfaceAmplitude e DampingFraction 4 This equation shows that at the damping depth the amplitude is reduced to 1 e or 37 of the surface amplitude Finally the temperature is computed as GA PS Vorcinn 3 5 TTeor c Manual 197 sim SoilTemp layer SurfaceMean Amplitude sin elapsed_secs Q Damping Fraction 5 where elapsed_secs is the number of seconds into the day which converts the frequency of the wave into a fraction of a day Note that DampingFraction has the effect of lagging the temperature wave as the depth increases GA PS Vorcinn 3 5 TTeor c Manual 198 6 GAPS for Programmers GAPS was written in the Turbo Pascal language Borland International versions 4 5 6 and 7 and 9 Delphi 2 over a period of seven years and growing by several programmers see acknowledgements Because of the multiple cooks the design and coding style is not always as consistent as we would like To compile the current version of GAPS you need the command line compiler tpc or bpc for Turbo or Borland Pascal 5 5 6 0 or 7 0 and the Turbo Vision 2 0 application framework The DOS interface was built using the object oriented application framework Turbo Vision 2 0 from Borland International The Turbo Vision source code and object files are copy protected If you want to re compile the GAPS source code you need to buy the Turbo Vision library from Borland Often Turbo Visio
219. potential are computed as AirEntryMFPlayer soil HydCondjayer soil AirEntryPotjayer 1 3 soil BValue 1 The procedure Matric Flux Potential is called at each time step to update the water status potentials and contents of the soil The first step is to estimate the current matric flux potentials from the volumetric water contents sim WN the saturation water content WS the air entry matric flux potential and the slope of the moisture release curve MFPlayer SC soil AirEntryMFPlayer E sim WN ayer WSlayer oll BValue 3 2 As in procedure Richards Equation this procedure then continues with series of sub procedures which are called iteratively until the mass balance is satisfied GA PS Vorcinn 3 5 TTeor c Manual 1N0 e Hydraulic Conductivities calculate unsaturated hydraulic conductivities for each layer from the current matric flux potentials e Soil Evaporation compute actual evaporation from the top soil layer e Jacobian set up simulataneous equations for determining new matric flux potentials from the current matric flux potentials water contents and hydraulic conductivities Thomas Algorithm solve this system of equations New Water Contents calculate the new water contents for each layer from the updated matric flux potentials These are called in turn as many times as necessary until the numerical solution of the modified Richards equation converges i e the mass bala
220. potential evapotranspiration using any method other than Pan your climate file does not need the field for Pan evaporation and your location file need not specify the pan and crop coefficients Refer to the description of each model procedure for the input data required for each one The following sections describe each file in more detail 3 4 1 1 Climate file File suffix cli Climate Data Files are used to tell the GAPS simulator about the daily weather These files can contain a maximum of one year of data 365 days for multi year simulations you must create a separate climate file for each year Data field Variable name Units of Modules in which field is used measure Minimum air MinTemp AirTemperature temperature Soil_ Temperature Harmonic Soil Temp Linacre ETP Penman_ETP SR_model Growth_Stages Max Photosynthesis Critical Leaf Water Potential Maximum air MaxTemp same as MinTemp temperature GA PS Vorcinn 3 5 TTeor c Manual 12 md Relative humidity RelHumid at dimension less Penman_ETP Richards Equation Tmax Matric Flux Potential Wind speed WindSpeed Penman ETP D m 3 Solar radiation SolRad MJ m d Atmos_Trans Priestley_Taylor ETP Penman ETP SR model Max_Photosynthesis SK_model dry_matter_accumulation 4 Precipitation Precip m Distribute_Precipitation Tipping_Bucket Richards Equation Matric_Flux_ Potential SR_model Water_Interception El S
221. procedure keeps track of the amount taken up so far 1 e above the next layer to be considered aboveUptake aboveUptake WUptake And the water available in this layer is reduced so that there will be less for the next plant LayerAvail layer LayerA vail layer WUptake time_step Note that after following this algorithm for the entire rooting profile there may be some unsatisfied demand This will be the difference between actual and potential transpiration for the crop The entire process is repeated for subsequent active crops 5 9 Water budget This procedure is called by the simulation driver at the end of each time step regardless of the soil water flow and plant water uptake models selected by the user to update several variables reported by GAPS in the simulation summary sum output file using the time step s values of corresponding variables just computed One set of variables relates to the accumulated water budget in kg m2 SumPotTrans SumPotEva total potential transpiration and evaporation SumActTrans SumEV total actual transpiration and evaporation GA PS Vorcinn 3 5 TTeor c Manual 192 SumWIn total water added to the profile e g rainfall SumDrain total drainage from the bottom of the profile SumWCChange cumulative change in profile water The current total profile water ProfileWater and the amount of this which is plant available ProfileAvail both in m3 m3 are also
222. r and AccTotalDryMatter after division by 10 to convert to kg m Finally the yield AccYield in t ha is calculated as AccYield AccTopDryMatter HIA plant_MinHl WUR WUR exp 6 13 8 83 WUR 100 plant_MinHI and HIJA plant HarvestIndex AccUnits AccUnits exp 11 1 10 AccUnts 100 WUR AccActTrans AccPotTrans WUR lt 1 where HTA is the simulated potential harvest index plant_MinHl is the minimum harvest index for the crop WUR is the water use ratio plant _HarvestIndex is the potential harvest index AccActTrans is the actual plant water use rate in mm d and AccPotTrans is the potential water use rate in mm d Plant height is limited by plant weight so that plants can t be unrealistically thin First the specific mass of the plant in kg pl is computed as PlantSpecMass AccTotalDryMatter kg m 2 plant PlantDensity pl ha 1 10000 m2 ha 1 y gt kg pl 1 Then the model checks whether this specific mass is too small to support the plant height that was calculated previously if so it limits the height accordingly if PlantSpecMass gt 0 0001 then if crop CanopyHeight PlantSpecMass gt plant_MaxHeightPerWeight then crop CanopyHeight PlantSpecMass plant MaxHeightPerWeight Public Function GetTransFrac The proportion of light intercepted for this crop as a monoculture is computed as GetTransFrac exp plant_ExtinctionCoeff LAI where LAI m
223. r and S Riha wheat and J Phillips fast growing tree SORKAM adapted by D Rossiter and S Riha from the work of Rosenthal et al 1989 EPIC adapted by P Simoens and S Riha from the work of Williamset al 1989 and CONSTANT by P Simoens These in turn have sub models specialized by crop species Stockle Riha or cultivar group SORKAM In GAPS crop model objects are created and destroyed dynamically that is during the execution not the compilation of the program Access to the objects is by means of pointer variables which contain a memory address of the object not the object itself and which must be dereferenced using the Pascal operator to access the object itself 5 4 1 Crop model generic source file croplib pas public procedures Begin Growth Daily Growth Begin TimeStep Growth Daily Growth_End End Growth TimeStep Stress open det file write summary a check model public functions GetTransFrac is_active is_transpiring has_matured private procedures grain moisture report progress This model implements the skeleton of a crop model and in addition implements behavior that is shared by all the descendent crop models status reporting based on plant and harvest date exploitation of soil layers by roots and grain drying Constructor Init This procedure is called by the simulation driver whenever any crop object is created at run time Its purpose is to initialize the s
224. r layer drainage and soil evaporation Drainage The profile drainage coefficient Profile_SWCON a fraction on 0 1 is used in the sub procedure Infiltration to limit the amount of water that can move out of a layer in one time step This is to reflect the fact that water must move through pores at a finite speed The drainage coefficient is thus a substitute for the saturated hydraulic conductivity GA PS Vorcinn 3 5 TTeor c Manual IN The profile coefficient is estimated as the slowest i e numerically smallest of the layer drainage coefficients SWCON which are estimated as the ratio of the pore space above the drained upper limit to to the total pore space SWCON WSjayer DULjayer WSlayer q Here WS which is the saturated water content m m3 1s taken as a direct estimate of the total pore space This formula implies that drainage is more rapid with a greater difference between saturation and field capacity which corresponds to more large freely draining pores Evaporation Evaporation from the soil surface is modelled in sub procedure Soil Evaporation That sub procedure needs a static estimate of 1 how deep in the profile evaporation is effective and 2 how dry each near surface layer can become solely due to evaporation These are determined as variables EvapLastLayer and P EvapFrac respectively This latter variable is a dynamic Pascal variable allocated on the heap at run time s
225. r of days and hours within each day to save Thus GAPS can be run on a system with no hard disk if need be Coprocessor A math coprocessor Intel 80x87 or functional equivalent is not required but will speed up the program considerably especially if computation intensive model procedures such as the Richards Equation or Soil Temperature are selected The installation procedure automatically selects the correct version ofthe GAPS executables for your system depending on whether or not a coprocessor is installed Numerical results are identical on systems with and without a coprocessor since floating point calculations on non coprocessor systems are performed by emulating the 80x87 Borland International s 8087 emulation library Monitor A graphics monitor is not required to run GAPS but is required to see the run time and post run graphics The graphics software uses Borland International s bgi graphics descriptor files and you need only install the one that matches your graphics adapter CGA EGA VGA Hercules IBM 8514 AT amp T 400 and IBM PC3270 graphics are all supported The batch version of GAPS called GSB requires 250Kb of free RAM It writes text to the screen using DOS calls and so does not require a graphics adapter Multitasking operating systems GAPS can run under several popular multitasking operating systems as a DOS task Under DESQVIEW 2 x GAPS requires a 300KB partition Other information for
226. rea during the pollination late lag and early grain filling growth stages 1f actual transpiration is less than 90 of potential transpiration LAlStressFact LAIStressFact 0 8 sim TRatio 1 where sim TRatio is the ratio of actual to potential transpiration Private procedure Dry_Matter_Accumulation This procedure is called at the end of each day to compute the amount of new dry matter produced during the day In this model daily dry matter accumulation DryMatter kg m2 dl 1s directly related to the daily photosynthesis SumPS g m2 dl using average conversion factor PSFact which depends on the growth stage DryMatter PSFact SumPS 1000 1 Daily photosynthesis SumPS is accumulated throughout the day in procedure Max Photosynthesis based on the time step s photosynthetic rate and possibly reduced by water stress in procedure Limit Photosynthesis The conversion factor is assumed to be 0 40 as suggested by Monteith 1981 during the vegetative growth stage During the pollination late lag and early filling growth stages this factor is assumed to be 0 33 after which it is zero 1 e no dry matter is accumulated during senescence The daily accumulated dry matter is partitioned into top and root dry matter following the method of Foth 1962 A partitioning factor PartFactor is calculated based on the number of days since plant emergence DAE days and the partitioning stage SR_PartitioningStage maintained by proc
227. res to be carried out at that time resolution depending on the model options selected by the user For example the subdriver for the elementary time step conceptually is as follows the actual code is in source file simula procedure TimeStep Procedures GA PS Vorcinn 3 5 TTeor c Manual 234 subdriver called at each time step procedure TimeStep_procedures begin atmospheric values SolarAngle Air_Temperature Distribute_Precipitation soil temperature case SoilTemp_method of Variable Numeric_Soil_Temperature_TimeStep Harmonic Harmonic_Soil_Temperature_TimeStep end potential ETP case ETP_method of Priestley Priestley_Taylor_ETP_TimeStep Penman S Penman_ETP_TimeStep Linacre Linacre_ETP_TimeStep Pan Pan_ETP_TimeStep end PartitionETP if ActiveCrops gt O then begin at least one crop is active competition model TheCompModel TimeStep grow the plants for crop_i 1 to global MaxCrops do if TheCrop crop_i lt gt nil and TheCrop crop_i is_transpiring then TheCrop crop_i TimeStep_ Growth take up water case Uptake_method of Potential_driven WaterUptake_TimeStep Plant_available SimpleWaterUptake_TimeStep Epic_water_uptake EPICWaterUptake_TimeStep end Uptake_method end at least one crop is active soil water flow case Flow_method of Richards_Equation Richards_Equation_TimeStep Tipping_Bucket Tipping_Bucket_TimeStep Matric_Flux M
228. rface several variables must be calculated These are found in sub procedure Soil Res of procedure Penman ETP Daily First the aerodynamic resistance to vapor transfer RA s m 1 for a soil surface is calculated based on the theory of turbulent transport if a windspeed at a specified height is known For a soil surface the zero plane displacement D is assumed equal to 0 m The momentum roughness parameter ZM is assumed equal to 0 01 m The vapor roughness parameter ZV is assumed to be 20 of the height of the momentum roughness parameter The calculation is thus RA LN loca WindHeight D ZV ZV In loca Windheight D ZM ZM K 2 clm Windspeed 2 where loca Windheight is the height above soil surface at which windspeed was measured m D is the zero plane displacement m ZM is the momentum roughness parameter 0 01 m ZV is the vapor roughness parameter 0 2 ZM K is the von Karman constant 0 4 and clim Windspeed is the measured windspeed m s 1 If windspeed is not known the aerodynamic resistance to vapor transport is assigned a constant value of 90 s m l Also in this procedure shortwave absorptivity ABS is assigned a value from the soil input file To apply the Penman Monteith equation to a crop surface these same variables must also be determinated These are found in sub procedure Crop Res of procedure Penman ETP Daily First an aerodynamic resistance for the boundary layer above the crop is calcula
229. rocedure dry matter accumulation as follows DailyLeafDryMatter 0 6 DailyTopDryMatter la DailyRootDryMatter 0 5 DailyTopDryMatter DailyGrainDryMatter 0 in fractionation stage 1 DailyLeafDryMatter 0 22 DailyTopDryMatter 1b DailyRootDryMatter 0 25 DailyTopDryMatter DailyGrainDryMatter 0 in fractionation stage 2 DailyLeafDryMatter 0 lc DailyRootDryMatter 0 25 DailyTopDryMatter DailyGrainDryMatter 0 in fractionation stage 3 DailyLeafDryMatter 0 1d DailyRootDryMatter 0 DailyGrainDryMatter 0 9 DailyTopDryMatter in fractionation stage 4 The grain yield if any is accumulated GA PS Vorcinn 3 5 TTeor c Manual 2 AccYield AccYield DailyGrainYield 2 and similarly for the roots AccRootDryMatter AccRootDryMatter DailyRootDryMatter 2 The rooting depth cm is determined as an empirical function of the total root dry matter and the base 7 C heat units accumulated since emergence AccUnits 1103 following SORKAM equation 44 RootingDepth plant MaxRootingDepth 0 5 0 5 sin 3 03 AccUnits1to3 GDD_to_4 1 487 plant SowingDepth 3 where GDD_to_4 is the number of heat units needed to reach anthesis This depth is of course limited to the maximum rooting depth specified in the plant input file Next the leaf area index is determined In growth stages 1 and 2 i e until the end of leaf growth it is determined from the specific
230. routine Structure In Jones C A and J R Kiniry eds 1986 CERES Maize A simulation model of maize growth anddevelopement College Station TX Texas A amp M University Press 194 pp Jury W A and C B Tanner 1975 Advection modification of the Priestley Taylor ET formula Agron J 67 840 842 van Keulen H amp Wolf J eds 1986 Modelling of agricultural production weather soils and crops Wageningen Pudoc Kiniry J R Williams J R Gassman P W amp Debaeke P 1992 A general process oriented model for two competing plant species Transactions ASAE 35 3 801 810 Lambers H A van der Werf and H Konings 1991 Respiratory Patterns in Roots in Relation to Their Functioning In Y Waisel A Eshel and U Kafkafi Eds Plant Roots the Hidden Half Marcel Dekker Inc New York pp 925 Linacre E T 1977 A simple formula for estimating evaporation rates in various climates using temperature data alone Agric Meteorol 18 409 424 McInnes K J 1981 Thermal conductivities of soils from dryland wheat regions of Eastern Washington M S thesis Washington State University Pullman GA PS Vorcinn 3 5 TTeor c Manual IER Monteith J L 1964 Evaportion and environment In the State and Movement of Water in Living Organisms 19th Symp Soc Exp Biol Monteith J L 1981 Climatic variation and the growth of crops Q J R Meteorol Soc 107 749 774 Monteith J L amp Unsworth M H 1990 Pr
231. rror FGauss for each node KL sim WPH KII 1 sim WP 1 1 FGauss I 1 N T NodeDeltal 1 1 K 1 1 sim WP I 1 KLI sim WP 1 1 NII NodeDeltal I GR KII 1 Kl sim WNLI WII KgFines I time_step where W is the old water content m3 m and sim WN is the new water content m3 m3 An appropriate mean water potential is calculated for each node using a weighted mean of the water potential at the i th time step and the water potential at the 1 1 th time step WP I n WPJ C n WPL 8 where J denotes time denotes the node number and n is a weighing factor between 0 forward difference or explicit method and 1 backward difference or implicit method When using the forward difference method fluxes conductivities and capacities are calculated using the water potential gradient at the beginning of the time step If n 1 fluxes are evaluated using the new water potentials only If n 0 5 the method is called time centered or the Crank Nicholson method and the arithmetic average of the water potential at the beginning and end of the time step is used to calculate fluxes of water The choice of n depends on the time constant of the system and strongly affects the numerical stability and accuracy of the solution When n 0 the solution can be unstable if the time steps chosen are too large or the fluxes of water entering the profile are great For water flow problems n 1 alm
232. rst_crop where first_crop is the first listed crop in the cropping sequence file that is active All other crops receive no radiation SolRad crop_1 0 SolRadFrac crop_1 0 where crop _i are all the crops except first_crop These two arrays SolRadFrac and SolRad are stored in the competition object and are provided to interested parties i e the respective crop models via the virtual access method MySolRad which is defined in the base competition model Its second purpose is to compute an overall potential transpiration fraction for all crops taken together to be reported with the access function GetTransFrac In the default no competition model this is simply the transpiration fraction from the first active crop which was computed immediately before as SolRadFraclfirst_crop TransFrac SolRadFrac first_crop Public procedure TimeStep This procedure is called by the simulation driver as part of its TimeStep Procedures each time step when there are any active crop models after solar angles precipitation soil temperature ETP computation and partitioning but before any plant procedures The default no competition model does nothing at this time scale Public function MySolRad This function supplies the daily solar radiation MJ m d available for one crop model This is simply the value of SolRad crop_i computed by the competition model as part of its daily procedure and stored for later access v
233. rvest or the end of the simulation This procedure sets the growth stage to none to stop crop simulation and calls the generic crop model s end growth procedure Public Function is_active This function returns True if and only if the crop object is active 1 e if the simulation driver should call any plant processes at all The crop is assumed to be active between the planting and harvest dates specified in the plant input file but in addition this function checks whether the crop simulation has been stopped by some other means in which case the growth stage is none Public Function is_transpiring This function returns True if and only if the crop object is transpiring i e actively growing in which case the simulation driver will call the crop s GetTransFrac function before partitioning potential evapotranspiration into evaporation and transpiration In this model the crop is transpiring only during the growth stages vegetative pollination late lag early filling and senescing Public Function has_matured This function returns True if and only if this grain crop has matured i e grain filling has stopped but grain drying is proceeding in which case the generic crop model s Daily_Growth_End procedure will simulate grain drying In this model this function is a direct translation of the matured growth stage Private procedure Water_Interception This procedure is called at each time step if the Water In
234. s these values can not be determined until emergence since they depend on the daylength See the description of procedure Emergence for this calculation Private Procedure Emergence This procedure is called at the end of each day when the plant is in growth stage 0 i e pre emergence to simulate the development of the seed and seedling until emergence If the seed has not yet germinated heat units base 6 3 C are accumulated until the threshold value of 18 is reached at which time the radicle has penetrated the seed coat Once the seed has germinated heat units base 11 4 C are accumulated until the threshold value of 51 is reached at which time the plumule has penetrated the seed coat Once the plumule has broken through the seed coat heat units base 11 4 C Units11 are accumulated and the plumule length is computed as Plumule_length Plumule_ length Units11 DCoeff 1 where DCoeff is the plumule extension rate a constant 3 1 cm c l When the plumule length reaches the sowing depth the plumule has emerged and the growth stage is changed to stage 1 Also if this is a tropical cultivar model option tropical the threshold degree days to stages 2 and 4 are computed from the daylength following SORKAM equations 4 and 7 as GA PS Vorcinn 3 5 TTeor c Manual AN GDD to_2 370 400 daylength 13 6 2 GDD to 4 GDD to 2 1020 120 daylength 13 6 3 ifthe daylength is greater
235. s layer GA PS Vorcinn 3 5 TTeor c Manual IAS Finally this procedure allocates storage for the evaporation fractions using the module variable P_EvapFrac and copies the evaporation fractions EvapFrac to the newly allocated array for use in the time step procedure Procedure Tipping_Bucket main procedure This is the control procedure called at each time step from the simulation driver Dynamic input to this procedure are the current volumetric water contents by layer W m3 m3 It first calls sub procedure Null_Settings to reset all inter layer fluxes Flux and the drainage rate DrainRate from the bottom of the profile to zero Then the water flux into the soil surface Flux MinLayer kg m2 is computed as Flux MinLayer WInput MinLayer time_step 1 where WInput MinLayer kg m2 sh is the rate of water addition to the surface for this time step of duration time_step s which was calculated in procedure Distribute Precipitation of the atmospheric processes library prior to this water flow procedure being called Next for each layer from the surface downwards the sub procedure Infiltration is called to move water into and out of the layer recomputing Flux layer to be the flux out of the layer and computing new water contents sim WN For all layers below the surface the layer s flux in is initialized to the previous layer s flux out The flux out of the bottom layer is the drainage rate Drain
236. ssRes 3 sim PotTrans 3600 9 PSStressFac GAPS Vorcinn 2 5 Tleer s Manual SPA 4 sim ActTrans 3600 10 1 PSStressFac 5 sim RootWP 11 LAIStressFac 6 leafWP Climateflux climfl txt CLF Data File Name C GAPS3 EXAMPLE CLF Date 5 24 1994 Time 10 44 8 Day Hour ETP ActEV ActTrans HeatFlux SimNetRad Airtemp AP SS W m2 C 1 12 84 4 84 4 0 0 0 0 230 1 10 12 133 7 133 7 0 0 0 0 280 1 1 2 20 12 106 5 106 3 0 0 0 0 314 7 9 0 30 T2 100 3 100 3 0 0 0 0 21232 Ru 40 12 140 1 0 0 0 0 0 0 317 3 FB 50 12 189 6 0 0 0 0 0 0 421 0 2 6 60 12 138 1 0 0 0 0 0 0 385 9 059 70 12 258 1 Paolo 0 0 0 0 399 6 7 8 80 2 397 6 0 0 0 0 0 0 595 6 9 0 90 12 440 8 252 4 0 0 0 0 636 8 10 4 00 iz 390 8 73 8 0 0 0 0 569 5 10 0 10 12 192 4 192 1 0 0 0 0 291 4 8 5 20 2 906 1 0 0 0 20 0 0 940 5 28 9 30 12 518 8 518 8 0 0 0 0 669 7 13 2 40 12 772 4 0 0 50 8 0 0 802 8 28 7 50 12 625 9 0 0 304 7 0 0 723 0 Zieh 60 12 483 0 11 3 68 2 0 0 555 2 21 4 70 12 960 8 0 0 30743 0 0 955 1 32 9 80 12 400 6 0 0 251 9 0 0 489 2 18 0 90 12 509 5 53 52 456 3 0 0 556 8 24 8 200 12 416 3 21 8 287 0 0 0 455 6 24 7 210 12 321 6 14 7 Baras UA 0 0 350 8 25 0 220 12 363 3 15 0 348 6 0 0 389 9 26 2 230 12 51971 26 7 247 8 0 0 591 6 22 0 240 12 321 6 2923 148 9 OQ IRA Pad ies Note that ETP ActEV and ActTRans are in units of kg m2 s in the CLF file 1 2 3 4 5 6 7 8 1 day 5 sim ActTrans ktw 2 hour 6 sim HeatFlux 3 sim ETP ktw 7 sim NetRad 4
237. sted by this procedure Thus the plant is considered to have a fresh source of carbon each day the photosynthate and a labile non structural carbon pool the reserve First the net photosynthesis NetPS kg m2 1s computed from the daily photosynthesis SumPS g m2 depending on the growth stage NetPS 0 60 12 44 SumPS 1000 in the vegetative stages up to booting la NetPS 0 80 12 44 SumPS 1000 after booting 1b Next the potential daily shoot growth ShootGrowthMax kg m2 is determined by a piecewise function which depends on the growth stage In the earlier stages this is a fixed amount ShootGrowthMax 7 2 x 104 from emergence until 2 leaves 2a ShootGrowthMax 4 05 x 103 2 or 3 leaves 2b In the later stages the function also includes a linear term based on the heat units accumulated since a specific growth stage was entered From jointing until the flag leaf is fully out this relation is ShootGrowthMax 6 48 x 103 3 672 x 102 AccDD AccDD to Jointed 389 2c From when the flag leaf is fully out until the end of flowering this relation is ShootGrowthMax 8 88 x 102 0 176 AccDD AccDD_to FlagLeafOut 176 2d From these functions it should be clear that potential shoot growth increases as the plant moves through the growth stages Maximum potential root growth is a constant 0 0025 kg m2 dl up until the end of flowering Next both the shoot and root potential growths are ad
238. t stress may be delayed by one time step for the first listed crop and advanced one time step for the other crops but this is a minor effect If there is only one crop this method is equivalent to the method of GAPS V3 and earlier Procedure SimpleWaterUptake Daily is called at the beginning of each day to calculate the total surface area of roots in the profile for each crop TheCrop crop_iJ TotalRoots m2 m3 from the root length density TheCrop crop_i crop RootDens m m3 and the thickness LayThick m within the rooting zone This can be done once a day because the rooting depth only can change daily LRoot crop_i TotalRoots RootsDens crop_i crop_i layer LayThick nyer 1 layer plant FRO gop i Procedure SimpleWaterUptake is called at each time step to compute the amount of rate of water uptake by the plant from each layer sim WUptake kg m elt and the rate of actual transpiration TheCrop crop_i ActTrans for each crop kg m el which is the sum of the uptake rates from the layers as well as the overall actual transpiration sim ActTrans which is the sum of the per crop transpiration This procedure works downwards from the top layer First the plant available water LayerAvail kg m in the layer is computed as the difference between the current water content sim WN m m and the wilting point soil DLL m mr converted to a mass LayerAvailli sim WN 1 soil DLL 1 KgFines
239. t units Before anthesis the base 7 heat units are accumulated into AccUnits1t03 After anthesis but before physiological maturity the base 1 heat units are accumulated into AccUnits4 The heart of this procedure is the attempt to move to the next growth stage This is based on a comparison of the accumulated heat units with threshold values GDD_to_2 GDD to 3 GDD to 4 and GDD 4 to 5 that must be reached in order to move to the next stage These threshold values are set as follows The base 1 degree days from anthesis to maturity are a constant 880 GDD_4 to_5 880 2 The base 7 degree days to reach the end of leaf growth is computed in the object constructor Init from the number of leaves NLeaves varietal coefficient 1 from the plant input file as GDD to_3 50 NLeaves 40 5 71 14 29 NLeaves 3 where the first term expands all leaves but the last at the rate of 50 degree days per leaf expansion and the last term expands the flag leaf SORKAM eqn 26 This expression substitutes for the simulation of individual leaf growth as found in SORKAM Note that later maturing varieties are those with more leaves For temperate cultivars model option temperate the remaining values are determined in the object constructor Init from the number of leaves following SORKAM equations 3 and 6 as GDD to 2 12 9 27 6 NLeaves 4 GDD to 4 289 72 45 84 NLeaves 5 For tropical cultivar
240. tate of variables shared by all crop models such as the accumulated and daily dry matter rooting depth etc Destructor Done This procedure is called by the simulation driver whenever any crop object of is destroyed at run time Its only purpose is to deallocate the heap space used by the object Even though the Pascal procedure is empty the compiler generates additional code to release the correct amount of memory from the heap Public procedure Begin_Growth This procedure is called by the simulation driver at the beginning of crop growth It logs this fact to the simulation summary file GA PS Vorcinn 3 5 TTeor c Manual dd Public procedure Daily_Growth_Begin This procedure is called by the simulation driver at the beginning of each day Its only function is to determine the soil volume exploited by roots As rooting depth calculated by the various descendent crop models increases additional layers of the soil profile containing roots are activated The root length density in each layer does not change from the values plant RootDens specified in the plant input file This means that once the rooting depth exceeds the upper boundary of a soil layer this layer is instantly fully exploited by roots according to the fixed root root density Public procedure TimeStep_Growth This procedure is called by the simulation driver at each time step when the crop is actively growing It is called after determining the current soil tem
241. ted based on the same equation used for calculating the aerodynamic resistance of the boundary layer above a soil However in this case the height of zero plane displacement D is no longer zero but assumed to be 64 of the canopy height m assigned in the plant input file updated The momentum roughness parameter ZM is assumed to be 13 of the canopy height and again the vapor roughness parameter ZV is assumed to be 20 of ZM Campbell 1977 If windspeed is not known then some assumed value plant RA for the aerodynamic resistance is called from the plant input file The canopy resistance can either be assigned and held constant or can be made a function of plant leaf water potential environmental vapor density deficit radiation air temperature or soil soil water potential factors depending on the crop being modeled either in this procedure or the null sub procedure Bulk Canopy Resistance Shortwave absorptivity is assigned a value from the plant input file The Penman Monteith equation is applied in the sub procedure Penman_ETP First net radiation sim NetRad W m 2 is calculated as the sum of absorbed shortwave radiation and net longwave radiation sim NetRad LWR SwAbs clim solrad real_day value 11 574 SpaRad SpaceSum 3 where LWR is net longwave radiation W m 2 SwAbs is the shortwave absorptivity of the soil soil SwAbs or crop plant AS clim SolRad is daily solar radiation MJ m 2 al being converted to
242. terception simulation option was selected by the model user It computes the amount of water intercepted by and evaporated from the canopy and the amount of throughfall i e water reaching the soil surface It adjusts the rainfall during the time step so that less water is applied to the soil surface for soil water balance calculations If there is any rain during the time step this procedure is called to compute the water intercepted by the canopy the total amount of water on the canopy CanopyWater kg m ground and the rate of throughfall to the soil WInput MinLayer i e the adjusted precipitation kg m2 sl The amount of water on the canopy is initially calculated as the amount of water previously on the canopy at the end of the previous time step plus the current time step s rainfall The throughfall to the soil is computed as the difference between this amount and the amount that the canopy is storing on its surface This amount is computed as the product of the plant Canopymax the amount of water potentially held per m of surface area of leaves which is input in the plant file and the current leaf area So if the canopy can store all this time step s water no precipitation reaches the soil otherwise the overflow amount from the canopy reaches the soil Water can then be evaporated from the canopy If the amount of potential transpiration kg m2 ground is greater than or equal to the amount of water stored on the canopy Ca
243. th windows dialog boxes can be moved around and have a close box which is equivalent to pressing the escape key Five basic types of onsceen controls can be present in a dialog box radio buttons check boxes action buttons input boxes and list boxes GA PS Vorcinn 3 5 TTeor c Manual TR Press the Tab key or Shift Tab to move the cursor from one group of controls to the other Use the arrow keys to move the cursor to the next or previous control To toggle a check box or radio button on or off press the space bar To select an action button e g Ok or Cancel press the Enter key with the cursor on that button Selecting the cancel button pressing Escape or clicking the close box will put away the dialog box without saving any changes With a mouse simply click on a button or box to select it 3 3 The menu The main menu contains the following options File Edit Graph Scenario Run and Window The menu options with their submenu options are discussed briefly below 3 3 1 File The File menu contains the options for creating editing and saving input and output files selecting the printer printing of any file shell to DOS and quit the program About displays some general information about GAPS 3 0 Press Esc or Spacebar or click Ok or press Enter to close the box New pops up a submenu with the 5 different types of input files climate location soil plant and save file After selection of one of these optio
244. the vegetative stage the relationships originally included in Stockle and Campbell s model and based on independent data sets of Acevedo 1975 have been synthesized to the following conversion from above ground dry matter AccTopDryMatter kg m2 LAI 7 6 AccTopDryMatter 7 Once vegetative LAI reaches a set value 4 1 in this model the expansion of leaf area slows down dramatically from the vegetative rate of 7 6 m2 leaf kel dry matter continuing at a rate of 0 5 m leaf kg 1 dry matter LAI 3 85 0 5 AccTopDryMatter 8 These two equations intersect at LAI 4 1197 but are not continuous in any derivative Development of LAI during the vegetative stage is not directly affected by water stress except as this affects photosynthesis and dry matter production By contrast during the pollination late lag and early grain filling growth stages leaf area is reduced as a function of attained leaf area index and thermal time since silking Dale et al 1980 with a correction for water stress as proposed by Stockle and Campbell 1985 The more water stress has been accumulated during the vegetative phase the more rapid will be the decline of leaf area The relation is LAI LAI at silking 0 035 FillingDD 1 AccLAIStressFact 9 where AccLAlStressFact is the accumulation in procedure Daily Growth End over the day of each time step s LAlStressFact calculated in procedure Limit Photosynthesis and Fillin
245. the record loca and so their variable names are prefixed by the record name e g loca Latitude A location file requires about 1 4Kb on disk 3 4 1 4 Plant file File suffix plt A plant data file describes the crop s management and static parameters e g its genetic characteristics Defaults for some variables are set in procedure clear_plant source file fileio pas The plant data file contains the following parameters Global variables GA PS Vorcinn 3 5 TTeor c Manual IR Data field Variable name Units of Modules in which field is used measure 1 Crop model Crop_option from the fixed list of crop models default none 2 Plant simulation proc status 1 9 dimension less model Crop record variables are global and loaded at crop initialization Data field Variable name Units of Modules in which field is used measure Sowing date SowingDate Day of year Default 1 Harvest date HarvestDate Day of year Default 365 Root radius RootRad m Default 0 002 Default 2 5 x 1010 Root resistance to water flow 3 Initial and limiting RootWP J kg root water potential Default 1500 Simula SR model Growth_stages is_active crop_model is_transpiring is_active Simula SR_model is_active SK_model is_active crop_model is_transpiring is_active WaterUptake SR_model Critical_Leaf Water Potential crop_model constructor but only used in SR_model The
246. tial may be set to a known value for example zero GA PS Vorcinn 3 5 TTeor c Manual 00 for a water table The potential could be set at some value that can be considered constant for the duration of the run Or there could be some depth at which no water flux is assumed to occur Writing 7 for each node and expressing the set of simultaneous equations as a tridiagonal matrix results in the so called Jacobian matrix shown below for a soil with four layers The BGauus terms are the diagonal elements the AGauss terms are the lower diagonal and the CGauss are the upper diagonal BGauss 1 CGauss 1 0 0 DP 1 FGauss 1 AGauss 2 BGauss 2 CGauss 2 0 TDP 2 FGauss 2 0 AGauss 3 BGauss 3 CGAuss 3 DP 3 FGauss 3 0 0 AGauss 4 BGAuss 4 DP 4 FGauss 4 where FGauss I is the mass balance error for node J and the elements of the Jacobian are computed as the derivatives of the mass balance term by the the water potential at the appropriate node i e above at and below the current node CGauss I d FGauss I d sim WP I 1 K I 1 NodeDelta I 10 BGauss I d FGauss I d sim WP K I NodeDelta I 1 K I NodeDelta I CP I GR N I K I sim WP I 11 except at the top node where the derivative of the water potential also includes the derivative of the rate of actual evaporation and there is no higher layer BGauss MinLayer d FGauss MinLayer d sim WP MinLayer
247. to differ with new active roots being more costly to maintain Lambers et al 1991 Growth respiration is calculated separately by decreasing that day s sum of GA PS Vorcinn 3 5 TTeor c Manual 71 photosynthate by 25 Johnson 1990 With respect to stem biomass it is assumed that only the outer living tissue is respiring and therefore the amount of biomass used in the above calculation is scaled down from total stem biomass The reference maintenance factors used are estimated from measurements of other woody species Rauscher et al 1990 Maintenance respiration at 20 C MRef New White Root Suberized Roots Stem Leaf The maintenance requirement is then subtracted from the existing biomass of that plant part with old and new root biomass calculated separately for each soil layer This procedure therefore accounts for death and senescence of root biomass If the growth allocated to each soil layer is less than the maintenance cost for that day there will be a net decrease in roots for that layer Private Procedure Suberize In order to account for the transformation of white fleshy roots to woody roots over time this routine transfers a fraction 0 03 day of the new root biomass in each layer to old root biomass Only new roots are used in the calculation of root water uptake but old roots which have a lower respiration rate and are therefore more stable over time provide the infrastructure for new root growth and w
248. ts full requirement and any left over is partitioned to leaf dry matter However if there is less photosynthate than the demand dry matter is divided according to the relative weights of the demands for stem and roots Root Part DryMatter Rt_Demand Rt_Demand St_Demand Siem Part DryMatter Root Part in which case no dry matter is allocated to leaves that day This assures that the canopy will not continue to expand until the tree has the ability to supply sufficient water to the leaves Private Procedure Distribute_Roots This procedure controls the distribution of new root biomass in the profile as a function of soil water potential and pre existing biomass The pre existing biomass BaseRtBio layer is calculated as all of the new root biomass plus half of the old root biomass The fraction to be allocated to each layer is calculated as PotGro layer BaseRtBio layer laythick layer 1 Pre_Dawn_WPflayer 500 RtGrowth layer PotGro layer sumPotGro Root Part where PotGro is the potential root growth in that layer under the conditions of the function defined and sumPotGro is the sum of potential root growth in all layers calculated for the purpose of defining the fraction Note that a pre dawn soil water potential Pre_Dawn_WP of 500 J kg is the lower limit for root growth 1 e no growth will occur in that layer as long as the pre dawn potential is 0 5 MPa or lower This assures that root growth is
249. ty 70 These could be all changed by a non programmer to allow more detailed or longer running simulations The penalty for increasing these limits is the extra space required to hold correspondingly larger data structures as well as longer running time for the additional time steps or soil layers To change these limits you simply need to edit the source file global pas with any text editor change the corresponding constant definition and then rebuild GAPS and GSB The resulting executables will incorporate the changed limits 6 2 Changing GAPS procedures It is certainly possible to change GAPS to suit your particular modelling needs There are three major classes of changes you might make 1 modifying an existing GAPS method GA PS Vorcinn 3 5 TTeor c Manual 120 2 expanding the method repertoire with another way of doing something that GAPS can already do and 3 expanding GAPS to simulate a phenomenon not now simulated An example of the first type of change would be changing the computation of light transmitted through the canopy as a function of leaf area an example of the second type of change would be adding another way of simulating soil temperature an example of the third type of change would be adding a simulation of the soil solution ionic equilibrium There are two problems with changing GAPS on your own First is that your changes may be incompatible with enhancements which we may make so t
250. uct heat i e its thermal conductivity and on the heat capacity of the soil The thermal conductivity of the soil is to a large degree a function of its water content and bulk density The procedure SoilTemperature Init is called at the beginning of the simulation to compute four empirical coefficients Coeffl Coeff4 which are used to estimate the thermal properties of the soil in the numerical solution of heat flow equations These coefficients are computed separately for each layer Coeff4 is the thermal conductivity when the soil is oven dry 1 e soil WN 0 and can be approximated from the moist bulk density soil BulkDensity Mg m3 following Campbell 1985 Coeff4 I 0 3 0 1 soil BulkDensity I 2 1 Coeff2 in part determines the differences in the thermal conductivity of saturated soils and is dependent on the total volume fraction of soils Campbell 1985 Coeff2 I 1 06 soil BulkDensity I 2 where 1 06 includes a correction for particle density assuming a particle density of 2 65 Mg m3 Coeffl also in part determines the differences in thermal conductivity of saturated soils and is based on work by GA PS Vorcinn 3 5 TTeor c Manual 124 DeVries 1963 Ifthe volume fraction of quartz is assumed to be zero and the value for particle density is assumed as above the computation is Coeffl I 0 65 0 78 soil BulkDensity I 0 6 soil BulkDensity I 2 3 Coeff3 determines the water
251. ule s procedures and the source file in which they may be found Any text editor may be used to examine the source files however a good programmer s editor such as Epsilon along with utilities such as Borland s text search utility grep supplied with the Turbo languages will greatly simplify such browsing 5 1 Structure of the simulation driver The simulation is time driven with procedures being called by the driver at various time steps yearly daily and sub daily e g hourly This latter time step is the one that can be controlled with the Simulation_Specs TimeStep menu choice The following psuedo code shows the conceptual structure of the simulation the actual code can be found in source file simula pas procedure manage 3 Lugaru Software Ltd Pittsburgh PA http www lugaru com GA PS Vorcinn 3 5 TTeor c Manual 22 year Integer day 1 366 day in year time_step 1 MaxTimeStep time step in day begin Begin_simulation_procedures for year first_year to last_year do begin Begin_year_procedures for day first_day to last_day do begin Begin_day_procedures for time_step 1 to num_of_time_steps do TimeStep_procedures End_day_procedures end for each day End_year_procedures end for each year End_simulation_procedures end Each of procedures procedures referred to as subdrivers in turn contains a list of the simulation procedu
252. urs i 2 Number of days n 5 NumberOfDays 00 50 200 250 300 to save i GAPS Vorcinn 2 5 Tleer s Manual 14N followed by n lines with the days i d Cropping Sequence file sequence def GAPS 3 5 Crop Sequence file extension SEQ Lines starting with the sign are ignored at input Comments added after the input data preceded by a are also ignored s single i integer b boolean s40 string 40 2 number of entries sowingYear i 1 is start of simulation sowingDate i I 3 60 harvestYear i must be gt sowingYear harvestDate i if harvestYear sowingYear must be gt sowingDate plantFileName s40 plt sowingYear sowingDate harvestYear HarvestDate plantFileName 1 2 365 itutor first plt constant 119 1 290 tutor second plt stockle maize competition model competition options loaded in fileio load sequence competition options 0 None 1 ALMANAC GA PS Vorcinn 3 5 TTeor c Manual 141 Input files Climate file example cli GAPS 3 0 climate file The climate file must be saved with the extension CLI Lines starting with the sign are ignored at input Comments added after the input data preceded by a are also ignored s single 1 integer s70 string 70 CMN11000 cli ClimateName s70 FirstDay i day of year 365 LastDay i day of year 1 input line for every day MinTemp s C
253. urve x1 f1 and x2 f2 read from the input file compete FitSCurve x1 fl x2 f2 yl y2 Destructor Done This procedure is called whenever an object of type SC_model is destroyed at run time Its only purpose is to deallocate the heap space used by the object Public procedure Begin Growth This procedure is called at the beginning of crop growth It is only used to set SE_GrowthStage to SE_leafIncrease Public procedure Daily_Growth_End This is called at the end of each simulated day Growing degrees days are calculated as GDD Tmax Tmin 2 plant BaseTemp and GDD gt 0 The growing degrees days are accumulated into AccDD The daily heat unit index AccUnits ranging from 0 at planting to 1 at physiological maturity is computed as AccDD divided by plant_PotUnits the potential heat units required for the maturation of the crop The leaf area index is simulated as a function of heat units crop stress and the development stage From planting to the start of leaf decline while the Acc Units is less than the plant_DeclineFraction the LAI is calculated as follows LAI LAI DeltaHUF plant_MaxPotLAI 1 exp 5 LAI plant_MaxPotLAJ sqrt CropStressFactor GA PS Vorcinn 3 5 TTeor c Manual RA where DeltaHUF is the daily change in the heat unit factor HeatUnitFactor plant_MaxPotLAl is the maximum possible LAI for the crop and CropStressFactor is the value of the minimum crop stress factor Wat
254. ut only the previous time step s estimates of root water potentials This procedure calls various private procedures to carry out the actual simulation namely Water Interception to determine how much water is intercepted by the plant canopy only if the Water Interception simulation option was selected by the model user Max Photosynthesis to determine the maximum photosynthetic rate and non stressed resistances either Critical Leaf Water Potential if the Critical Leaf Water Potential simulation option was selected by the model user or Simple Water Stress otherwise to determine a water stress coefficient and Limit Photosynthesis to limit photosynthesis by this coefficient Finally this procedure keeps a running total of the daily photosynthesis and stress factor Public procedure Daily_Growth_End This procedure is called by the simulation driver at the end of each simulated day It controls the major plant growth processes by calling the following private procedures and functions e Growth Stages transition between growth stages Dry Matter Accumulation accumulate dry matter e Yield accumulate grain GA PS Vorcinn 3 5 TTeor c Manual 47 This procedure also accumulates stress indices for reporting at the end of the simulation and calls the generic crop object s end of day procedure Public procedure End_Growth This procedure is called by the simulation driver at the end of crop growth i e at ha
255. vaporation This procedure is called at each time step to determine the actual evaporation from the soil surface and to reduce the volumetric water content of the near surface layers accordingly It follows a simple model of GA PS Vorcinn 3 5 TTeor c Manual 107 satisfying the total evaporative demand downward from the surface by layer very much as the tipping bucket infiltration fills each layer before water moves down The mass of water water_evaporated kg m7 that can be evaporated from a layer during the time step is calculated as water_evaporated KgFines layer sim WN layer soil DUL layer P_EvapFrac layer 1 where KgFines kg m7 converts from volume to weight sim WN is the current volumetric water content for the layer as computed in sub procedure Infiltration m3 m3 soil DUL is the field capacity water content m3 m3 and P_EvapFrac is the fraction on 0 1 of field capacity to which the layer can be dried by evaporation These fractions are computed once for the entire simulation in procedure Tipping Bucket Init Thus the term soil DUL layer P_EvapFrac layer 1 represents a limiting water content below field capacity to which evaporation can dry the layer n b the layer can dry to field capacity simply by drainage Of course there must be evaporative demand to actually dry the soil so the above calculation is contained in a loop which works down from the surf
256. want s to be its value for moist conditions i e s2 and at FFC 0 0 s must be its value for dry conditions i e sj These three values of sy are computed directly from the corresponding curve number CN using the basic relation between curve number and retention parameter sx 254 100 CNS 1 7 where the factor 254 converts from the 0 1 scale of curve numbers to kg m i e mm of water Once the three values sj 2 3 have been computed the shape parameters w andw2 are computed from the solution of the simultaneous equations w2 2 0 5 Inf 0 5 1 s2 s1 In 0 0 s3 s1 1 8a wi w2 ln 1 0 s3 81 1 8b There is one further adjustment to the daily retention parameter that is made if the soil temperature in the second layer of the profile is below freezing The following empirical equation is used to decrease retention s s 1 e 0 00292 s 7 if sim SoilTemp 3 lt 0 C 9 This increases runoff for frozen soils at high values of s i e under wet conditions but has little effect on runoff for dry soils This adjustment is still made even if soil temperature is not being simulated in which case the initial value of soil temperature soil InitSoilTemp 3 default 20 C is used throughout the simulation 5 8 Plant water uptake soil plant interface GAPS provides three ways to simulate plant water uptake potential driven and plant available and the Epic m
257. xample seq GAPS 3 5 Crop Sequence file extension SEQ Lines starting with the sign are ignored at input Comments added after the input data preceded by a are also ignored s single 1 integer b boolean s40 string 40 2 number of entries sowingYear 1 1 is start of simulation sowingDate i 1 23 65 harvestYear i must be gt sowingYear harvestDate i if harvestYear sowingYear must be gt sowingDate GA PS Vorcinn 3 5 TTeor c Manual 147 plantFileName s40 pit sowingYear sowingDate harvestYear HarvestDate plantFileName T t 2 365 en EE EES Le constant 1 119 1 290 tutor second plt stockle maize competition model 1 competition options loaded in fileio load sequence competition options 0 None 1 ALMANAC Scenario file example set GAPS 3 0 scenario file extension set Lines starting with the sign are ignored at input Comments added after the data preceded by a are also ignored no file selected s single i integer s70 string 70 GAPS V 3 0 version 2 i number of simulation years C GAPS3 EXAMPLE CL s70 climateFileNames n C GAPS3 EXAMPLE CL s70 climateFileNames n C GAPS3 EXAMPLE LOC s70 locationFileName C GAPS3 EXAMPLE SOL S70 soilFileName C GAPS3 EXAMPLE PLT S70 plantFileNames n s70 plantFileNames n C GAPS3 EXAMPLE SAV
258. xt from the document and places it temporarily in the clipboard You can then paste it into one or more documents by choosing Paste Copy copies the selected text from the document in the clipboard It can be pasted then into one or more other documents by choosing Paste Paste inserts the text from the clipboard into the current window at the cursor position Clear removes the selected text from the document but does not put it into the clipboard Show clipboard opens the Clipboard window which stores the text you cut and copy from other windows 3 3 3 Graph The Graph menu lets you display the postrun results graphically or if Print variables is checked output will be directed to the print queue printer or text file Daily summary pops up the open file dialog After selection of a daily summary output file extension sum the PostRun Graphs dialog box appears Enter the time range and the graphs to view maximum 4 graphs can be displayed Press any key to return to the menu after viewing the graphs Layers soil pops up the open file dialog After selection of a layers output file extension lay the PostRun Graphs dialog box appears Enter the time range the graphs to view maximum 4 graphs can be displayed and the layers Press any key to see the graphs for the next selected layer Soil flux pops up the open file dialog After selection of a soil flux output file extension sof the PostRun Graphs dialo
259. zmann constant 5 67E 08 W m 2 K 4 AirTemp is the air temperature C being converted to K by adding 273 Atmospheric emissivity can be calculated according to Campbell 1985 as EA 1 0 84 Clouds 0 72 0 005 AirTemp 0 84 Clouds 4 where Clouds is the fractional cloud cover taking values between 0 and 1 and is calculated in module Atmos_Trans The slope of the saturation vapor density function SSVD kg m 3 K 1 i e the change in saturation vapor density with a change in temperature is given by Fuchs et al 1978 as SSVD SVD LAMB MW R AirTempK 1 AirTempK 5 where LAMB is the latent heat of vaporization of water 2450 J g 1 MW is the molecular weight of water 0 018 kg mol 1 R is the gas constant 8 3143 J mol 1 K 1 AirTempK is the air temperature K and SVD is the saturation vapor density g m 3 This latter is given by Campbell 1985 as SVD EXP 31 3716 6014 79 AirTempK 0 00792495 AirTemp K AirTempK 6 5 3 2 Penman The Penman Monteith equation combines a vapor diffusion and energy budget approach to predict evapotranspiration from plant canopies Monteith 1964 applied the Penman equation 1948 to crop canopies arguing that the resistances to vapor diffusion from inside the leaves through the stomates leaf boundary layer and canopy could be incorporated into a single canopy resistance Net radiation must be known change in soil heat storage either known or assu

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