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1. and absolute growth rate AGR for the 30 day 7 harvesting interval of P 5 360 pr maximum cv Trichoglume T 12000 5 cv Petrie Green Panic as E o estimated by the successive 3 5 o harvests approach 2001 02 ce NA 270 As growth season La Maria E vA N oe ei Experimental Ranch INTA E Sii x Y Oo Santiago del Estero Y in 92 Argentina References e 9 33 rainfall AGR and growing 180 ag degree days GDD 2 correspond to the period 2 a comprised between S 4000 Tey at To a sampling dates i ee Pe ea D 90 3 EH E cl E S 8 S S S 5 Cu Ey e cy D oy ol ol a q 2 a S 2 S 8 E x 3 a a Date mo Rainfall BV ds AGR us GDO int Initialphiase Middlephase Finalphase biomass accumulation BM 12000 00 Initial phase Middle phase Final phase 450 and absolute growth rate AGR for the 15 day 1 harvesting interval of P 2 maximum cv Trichoglume E 360 3 cv Petrie Green Panic as estimated by the successive Z Q gt harvests approach 2002 03 E 8000 00 1 growth season La Maria 9 g ja Experimental Ranch INTA ser iT 240 z gt Santiago del Estero oO 2 3 3 Argentina References E l Sone rainfall AGR and growing 20 j i P ae degree days GDD es lL As XQ 180 22 correspond to the period 3 4000 00 e comprised between a 3 sampling dates 3 3 0 00 Mi j E L Se sSsgsgses8e8
2. nas PWP 19 69 LS 9p 87 0 Aep IDUIS S Rp Jo Joquinyy y uef cI 99d 8c 99d LI 9q uel PeArosgo qA JU3 U09 137EM 105 0 S0 z0 0 0 0T 0 T 0 Z 6T 0 PO Z0 0 T TZ 20 21 2T ZO TT TZ z0 0T 80 Dates Fig 7 Dynamics of soil water content SM for a 2000 01 b 2002 03 and c 2002 03 growth seasons at two soil depths 0 15 and 15 30 cm La Maria Experimental Ranch Santiago del Estero Experimental Station Argentina References PWP permanent wilting point Panic growing under full sunlight in the Chaco by De Le n et al 1995b and by Obispo et al 2008 for a silvopastoral system under medium shade In this study the grazing history was represented by the harvesting interval and by the stubble height or PoyUNOd sem BAJOJUT SUNSoAIeY ous AVG 956 90 Lt SELTI ec 66 SL ESI _Aep 24 WC 3 PIPA yeod YO V 18 Ol 190 97 PO 9 99d 0 tg og SI og SI 8C skep S BAJ9 UI SUISIAIEH 202007 co 1007 100007 uoseas ymo eunuogIy 019 54 S SIAJBY IAISSIDINS S9JBI YIMOIS IANJOSQR sseworq PUNOIS9AOge paje pnunsoy J AQEL plant tissue left for the plant to recover after the pringer BS 10 de 15 Sitio Argentino de Producci n Animal Agroforest Syst 45 O O 225 S A E 17 Apr 02 D 3 Apr 02 14 Mar 02 27 Feb 02 11 Feb 02 AS 21 Jan 02
3. Ammerman C 1998 Statistical analysis of repeated measures data using SAS procedures J Anim Sci 76 1216 1231 Ludwig F De Kroon H Prins H 2008 Impacts of savanna trees on forage quality for a large African herbivore Oecologia 155 487 496 Morello J Adamoli J 1974 Las grandes unidades de vegeta ci n y ambiente del Chaco argentino Segunda parte vegetaci n y ambiente de la provincia del Chaco INTA Serie fitogeogr fica No 13 Buenos Aires 130 pp Moreno X Salazar A Villasmil J Urdaneta M 1995 Com portamiento fisiol gico del pasto guinea Panicum maxi mum Jacq sometido a diferentes frecuencias y alturas de corte I Distribuci n de biomasa y an lisis del crecimiento Revista de la Facultad de Agronom a Universidad del Zulia 12 Maracaibo pp 313 323 Obispo N Espinoza Y Gil J Ovalles F Rodriguez M 2008 Efecto del sombreado sobre la producci n y calidad del pasto guinea Panicum maximum en un sistema silvo pastoril Zootecnia Tropical 26 285 288 O Reagain P Ash A 2002 Principles of sustainable grazing management for the northern savannas In 12th Biennial Conference The Australian Rangeland Society 2 5 Sep tember 2002 Kalgoorlie Western Australia Consulted September 2013 in http era deedi qld gov au 185 Overman A Scholtz R III 2002 Mathematical models of crop growth and yield CRC Press Boca Raton Penton G 2000 Tolerancia del Panicum maximum cv Likoni a la sombra en condiciones co
4. In all harvested material leaf and shoot fractions were separated by hand and weighed Results were expressed as kg of dry matter per hectare kg DM ha Weather and soil moisture monitoring Rainfall at the study sites was collected in a micro raingauges located near the sampling plots Data were collected every 2 weeks during the wet season Rainfall mm and air temperature C collected at the INTA Meteorological Station located in the Ranch headquarters 7 km from the experimental area were used as a master record since observations are taken every day Data of air temperature were used to calculate the growing degree days observed between sampling dates GDD as follows Gomez de la Fuente et al 2007 Smart et al 2007 GDD 2 Tanase Taaa 2 Thae 1 where T max 18 the maximum air temperature C T nin is the minimum air temperature C and Thase 1S 15 C Growth of Green Panic is restricted at air temperatures lower than 15 C Ivory and Whiteman 1978 while optimum air temperature for photosyn thesis is 34 C Chacon Moreno et al 1995 Soil water content SM was assessed by the gravimetric method in each harvesting date Three random samples were taken near the cages at two soil depths 0 15 cm SM15 and 15 30 cm SM30 Forage quality analysis Samples of BM comprising total leaf and shoot fractions gathered for the estimation of the growth curve 2000 01 were hand separated and ana
5. and greater than the reported productivity of native open grasslands estimated as 5 000 kg DM ha of standing crop Kunst et al 2006 Parameters of forage quality were also very similar This information suggests that Green Panic is a good choice to reclaim paddocks in poor range condition and dominated by woody plants without drastically altering the ecosystem sustaining the approach of creating an agroforestry system in the Chaco Environmental impact is reduced when trees and shrubs are maintained in a paddock Jackson and Ash 1998 Obispo et al 2008 In fact soil structure fertility porosity and water storage capacity are improved under trees and shrubs a fact reported for the Chaco region in experiments involving roller chopping treatments Anriquez et al 2005 Ledesma A Springer 11 de 15 Sitio Argentino de Producci n Animal Table 2 Growth features of Panicum maximum cv trichog lume cv Petrie green Panic under woody cover as estimated by the functional approach for three growth seasons 2000 01 Season Harvesting Parameters Estimate Error intervals days 2000 01 28 a 9205 14 b 0 73 C 0 040 d 3 25 2001 02 15 a 6922 42 345 22 b 15 68 4 66 C 0 04 0 01 30 a 12237 06 840 8 b 27 86 13 27 C 0 04 0 01 2002 03 15 a 3503 91 176 88 b 11 14 3 29 C 0 03 4 5E 03 30 a 5735 21 587 2 b 48 22 60 88 C 0 04 0 01 Agroforest Syst 2001 02 and 2002 03 La Maria Experimental Ranch Santiago del Estero
6. Animal Agroforest Syst Forage quality During the 2000 01 season the leaf shoot ratio was 1 6 2 1 from the beginning of the growth until the end of February and then the ratio increased up to seven toward the end of the season Fig 8 The other two seasons presented similar results The mean protein content of the leaf and shoot fractions were 14 76 and 7 93 respectively Mean acid detergent fiber was 69 93 and 76 for both fractions respec tively In the 2001 02 season the leaf shoot ratio increased again toward the end of the season in both harvesting intervals but the 15 day harvesting interval showed the largest increase Environmental dynamics In the 2000 01 2001 02 and 2002 03 growth seasons the total rainfall amount in the study area was 577 739 8 and 891 7 mm respectively The GDD were 1 492 1 643 and 1 956 C for the same seasons respectively The last growth season was unusual the rainfall showed two peaks one at the beginning and another at the end of the growth season separated by a period of low rains and a peak of GDD during January Figs 5 6 During the first season the soil moisture showed an increasing trend and was above the soil wilting point at the end of the study period Fig 7a On the other hand soil moisture presented a decreasing trend in the second and third seasons Fig 7b c being the mean soil moisture content consistently under the potential wilting point during the third se
7. Experimental Station Santiago del Estero Argentina p value R Time to inflection Max C kg DM point since ha day day 0 days 0 98 22 160 96 lt 0 0001 0 983 69 67 47 0 0083 0 01 0 0001 0 989 83 116 96 0 1037 0 0046 lt 0 0001 0 98 80 34 29 0 0117 0 0002 0 0103 0 982 97 56 69 0 51 0 0924 a maximum aboveground biomass accumulation BM kg DM ha b starting coefficient c intrinsic rate of increase of aboveground biomass accumulation kg DM ha day For other references see text 2006 Albanesi 2012 Albanesi et al 2012 Anriquez et al 2012 and other ecosystems Belsky et al 1993 Obispo et al 2008 Also shade increases livestock comfort and forage has a better nutritional quality Bordon 1988 Belsky et al 1993 Ledesma 2006 Treydte et al 2007 Ludwig et al 2008 Obispo et al 2008 The recurring periods of grazing and resting of a pasture require quantitative assessment on forage growth rates and how these growth rates vary throughout time and the influence on environmental factors so both productivity and persistence are maintained Gillen and McNew 1987 In semiarid arid areas the forage quality is of lesser importance than yield since the rainfall regime is seasonal and the opportunity to replace grazed organs is directly related to water availability and proper resting so the removal of tissue is equilibrated by the growth processes The harvesting intervals in this study were selected
8. between 3 500 and 11 500 kg dry matter ha The absolute growth rate presented two M Casta ares Private consultant C Kunst lt R Ledesma M Casta ares M Cornacchione H van Meer J Godoy Instituto Nacional de Tecnolog a Agropecuaria Estaci n Experimental Agropecuaria Santiago del Estero Jujuy 850 G4200CQR Santiago del Estero Argentina e mail kunst carlosOinta gob ar Published online 14 December 2013 annual peaks located in early and late summer irrespective of growth season and harvesting interval Growth season and harvesting interval significantly affected the relative growth rate p gt F 0 0015 and p gt F 0 0002 respectively BM was significantly correlated with rainfall and GDD observed between sampling dates the magnitude of the coefficients were higher for the 30 day than for the 15 day harvesting interval Correlation between BM and soil moisture content was not significant for both soil depths Resting periods should be longer than 30 days to maintain the stability of the grazing system Keywords Biomass Growth rate Roller chopping Silvopasture Harvesting interval Introduction The original vegetation of the Chaco region of Argentina was a mosaic of forests woodlands savan nas and shrublands Morello and Adamoli 1974 Timber operations exceeding regeneration rates live stock overgrazing and misuse of fire have caused an increase of woody plant species in the curre
9. empirically based on the pattern of storms Y Springer that bring moisture to the Chaco environment They give an insight of the grazing interval needed to assure the persistence of Green Panic pastures in roller chopper paddock information related to both economic and ecological sustainability of livestock operations In semiarid arid areas the period of resting deferment plays a key role in the sustainabil ity of a pasture throughout time Reese 1993 O Reagain and Ash 2002 The information gathered in this research suggest that for a roller chopped paddock with Green Panic in the Chaco a grazing system with a resting interval higher than 30 days and stubble heights higher than 10 cm could be recommended to get high yield high water efficiency and appropriate persistence of the plants throughout time Results also indicate that a paddock may be grazed 2 3 times during the rainfall season a fact that should be taken into account when planning average stocking rates and persistence in time of a pasture 12 de 15 Sitio Argentino de Producci n Animal Agroforest Syst Table 3 Kendall s t correlation coefficient and A its significance between Growth season Environmental variables BM environmental variables and lt SS gt RHRXRH2RNR accumulated aboveground 01 02 Rainfall between sampling dates T 0 55 ce ae in each p gt ltl 0 002 t i E E Growing degree days T 0 38 maximum cv trichoglume c
10. on the temporal dynamics of the aboveground biomass BM of Green panic were gathered using the method of successive harvests as proposed by Anslow and Green 1967 Two groups of four permanent fixed plots of an area of 1 m each total n 8 were randomly laid in the center area of the first paddock at mid distance from the watering point and the opposite corner in order to avoid highly trampled soils Locally plots were located at an equal distance from the nearby tree shrub under their canopies Fig 1 and protected from grazing by cattle by a wire cage Tee vb e te ir E A pit e a Weee ae i A tir pr s ML peg A Y 5 el 4 I a b fie og Ly gt i k PA n EN 1 n t P hz E ing ta AE A pak lak 7 Os F 5 Pjan aR fixed in the ground by iron stakes An area of 0 25 m located in the center of each plot was harvested using hand scissors and stored in a paper bag There was an average of 12 plants of Green Panic in each 0 25 m plot The rest of the grass plants within a cage were harvested immediately after the samples were taken and the residues were left in the ground The harvesting frequency of both plot groups was 28 days but with a 14 day gap between them from December 2000 and March 2001 Casta ares 2002 In a second step of the research the effect of the harvesting interval on BM and on the relative growth rate of the species was assessed in the second paddock Harvesting intervals of 15 and 30 d
11. 1s the BM as estimated by the functional approach Fig 3 Aboveground biomass accumulation BM and absolute growth rate AGR for the 15 day harvesting interval of P maximum cv Trichoglume cv Petrie Green Panic as estimated by the successive harvests approach 2001 02 growth season La Maria Experimental Ranch INTA Santiago del Estero Argentina References rainfall AGR and growing degree days GDD correspond to the period comprised between sampling dates Y Springer Accumulated aboveground biomass Accumulated aboveground biomass kg DM ha kg DM ha dIt1O Argentino de Froduccion Animal Agroforest Syst D j pam el Ti a e a 8 2 5 2 2 2 a 3 3 E amp es B 2 RH A g 5 g Dates ms Rainfall O BM Plotgroup1 BM plot group 2 BM curve s k AGR a GDD 12000 8000 4000 V Km x gt l 1 1 26 11 2001 A 15 10 2001 29 10 2001 12 11 2001 de 10 12 2001 24 12 2001 07 01 2002 21 01 2002 04 02 2002 18 02 2002 18 03 2002 01 04 2002 15 04 2002 04 03 2002 Dates MO Rainfall BM lt GDD i AGR 6 de 15 180 120 60 360 180 95 dao Aep e4y Ng 34 9181 ymo 33n 0Sq y 90 Ga Aep 1 24 NO 34 yo WW sajep Sulj dwes usamjeq jejuiey ww pejurey DItO Argentino de Froduccion Animal Agroforest Syst Fig 4 Aboveground 7 e 450 biomass accumulation BM hase Middle phase
12. 88388 8 9 9 Fu FT ggg gg se ag SSsSsAR RRS EE ES FG om A N m y D N 5 2 N o g Dates E Rainfall BM a AGR x GDD A Springer 7 de 15 SAICO Argentino de Froduccion Animal Agroforest Syst Fig 6 Aboveground 12000 700 biomass accumulation BM and absolute growth rate AGR for the 30 day Ps harvesting interval of P 600 maximum cv Trichoglume 5 cv Petrie Green Panic as c f 2 gt i o h estimated by the successive 500 a harvests approach 2002 03 ar growth season La Maria 2000 7 ad 2 Experimental Ranch INTA 3 q 4 do E G D Santiago del Estero od 400 y gt 5 Argentina References io p A 4 4 rainfall AGR and growing z 7 sa e D 5 degree days GDD 2 y a correspond to the period e y 300 2 a comprised between o bg sampling dates ED d pd pung y 4000 3 2 200 3 4 100 0 i ns 0 EN el el mm m7 a nm oy o o o O y oy a A a iy dy e 6 5 3 3 Date MS Rainfall ome Bh 4 AGR GDD peak presented a larger magnitude than the second AGR peak in the three growth seasons studied Figs 2 3 4 5 6 The mean total accumulated BM of Green Panic in these 6 7 months calculated by the harvesting method varied between 3 500 and 11 500 kg DM ha Figs 1 2 3 4 5 The logistic and Richards functions fitted well the accumulated BM data throughout time R 0 98 in all cases Table 2 The asymptote of t
13. Sitio Argentino de Producci n Animal Agroforest Syst DOI 10 1007 s10457 013 9663 4 Yield and growth features of Panicum maximum Jacq var Trichoglume cv Petrie Green Panic under woody cover Chaco region Argentina C Kunst R Ledesma M Casta ares M Cornacchione H van Meer J Godoy Received 16 May 2013 Accepted 7 December 2013 O Springer Science Business Media Dordrecht 2013 Abstract Secondary forests and shrub thickets with low suitability for cattle raising are widespread in the Chaco region NW Argentina Concerns about the ecological sustainability of these ecosystems favor vegetation clearing methods for improving standing forage and accessibility for livestock operations that retain native tree and shrub species a system called silvopasture locally These areas are characterized by a reduction of sunlight availability if compared with treeless pastures The objective of this research was to assess the growth rate and the effect of two harvesting intervals 15 and 30 days on the annual yield BM and forage quality of Panicum maximum Jacq var Trichoglume cv Petrie Green Panic in such a system using two approaches successive harvests and functional during three growth seasons 2000 01 2001 02 and 2002 03 Correlation of growth features of Green panic with rainfall mm growing degree days C GDD and soil moisture at two soil depths 0 15 and 15 30 cm was also assessed BM varied
14. al grasses I Effect of day and night tem perature on growth and morphological development Aus J Plant Phys 5 131 148 Jackson J Ash J 1998 Tree grass relationships in open euca lypt woodlands of northeastern Australia influence of trees on pasture productivity forage quality and species distri bution Agro Syst 40 159 176 Khan ACh 1971 Rainfall pattern and monthly forage yields in the Thai ranges of Pakistan J Range Manag 24 66 70 Kiss Trocsanyi Fieldsend A Wolf D 2009 Yield and canopy characteristics of switchgrass Panicum virgatum as influenced by cutting management Biomass Bioenergy 33 442 448 Kunst C Ledesma R Basan M Angella G Prieto D Godoy J 2003 Rolado de fachinales e infiltraci n de agua en el suelo en el Chaco occidental argentino Rev Inv Agrop 32 105 122 A Springer Agroforest Syst Kunst C Monti E Perez H Godoy J 2006 Assessment of the rangelands of southwestern Santiago del Estero for graz ing management and research J Environ Manag 80 248 265 Kunst C Ledesma R Bravo S Albanesi A Anriquez A van Meer H Godoy J 2012 Disrupting woody steady states in the Chaco region Argentina responses to combined dis turbance treatments Ecol Eng 42 42 53 Ledesma R 2006 Desarrollo de sistemas ganaderos una al ternativa de manejo en ecosistemas degradados del Chaco semi rido Masters Thesis Universidad Nacional de San tiago del Estero Santiago del Estero p 134 Littell R Henry P
15. and shrub species Provincia de Santiago del Estero Law 6841 and further regulations 2007 and paddocks reclaimed with the procedure described above are commonly called a silvopasture In this context Green panic has a clear advantage over other grass species because its forage production is not adversely affected by shade Tavares de Castro et al 1999 Smit 2005 Ledesma 2006 Successful grazing management of the system described above requires quantitative information about the forage quantity cycle i e annual forage yield and growth rates of the key grass species Vallentine 2001 Yield forage quality the effects of harvesting frequencies and environmental features on varieties and species of Panicum have been studied in several ecosystems Eriksen and Whitney 1981 Moreno et al 1995 Durr and Rangel 2000 Penton 2000 Obispo et al 2008 Ramirez Reynoso et al 2009 However there is a lack of such information for Green panic growing under a vegetation structure created by a roller chopping treatment in the Chaco region Considering this paucity the objective of this research was to determine a total annual above ground biomass yield b growth rates and c the effect of harvesting intervals on the relative growth rate and the aboveground biomass yield of the species in a roller chopped pasture Relationships of these species features with environmental variables such as Y Springer Agroforest Syst rainfa
16. ason Fig 7c In all cases the soil moisture was higher at the top soil horizon than at the deeper soil horizon at the beginning of the growth period and then slowly decreased Correlations between growth features and environmental variables At the seasonal scale the higher accumulated BM were observed in the 2002 01 season and the lowest in 2002 03 season irrespective of harvesting interval Table 2 Although the third growth season presented the highest total rainfall of the three seasons the annual accumulated BM was the smallest of the three showing a decrease in both harvesting intervals Figs 4 5 At the intra seasonal scale the annual time series of BM was significantly correlated with the time series of the rainfall and the GDD between sampling dates Table 3a The time series of BM sorted by harvesting frequencies presented the same significant correla tions but the magnitude of the coefficients were higher for the 30 day harvesting interval than for the 15 day harvesting interval Table 3b Correlations between the mean BM and the mean SM were not significant for both soil depths Discussion The average maximum yield of Green Panic in this study ranged from 3 500 to 11 500 kg DM ha for the lower and higher harvesting interval respectively Table 1 The reduction of the photon flux observed in this study is similar to those reported in other studies involving roller chopper treatments suggesting a
17. ays were applied at two groups of four plots each using the same procedure described above These harvesting intervals were selected empirically taking into account the rainstorm pattern of the Chaco rains are usually frontal resulting from the clash of tropical hot fronts with cold southern winds occurring somewhat cycli cally from late spring to early fall approximately every 7 10 days Ledesma N personal communica tion Therefore a minimum sampling period of 15 days would increase the likelihood of at least one storm occurring between sampling dates Sampling was performed during two growth seasons from November 2001 to April 2002 and from November Fig 1 Scheme showing the position of a plot in relation to tree and shrub canopies Wire cage not shown Y Springer 3 de 15 Sitio Argentino de Producci n Animal 2002 to April 2003 respectively Plot location was changed every year using the same sampling proce dure as described In both stages of the study the initial sampling date day 0 was selected based on weather forecasts for the study area and at least 3 days before a rain In that sampling date all plants in a plot were cut and the residues discarded Throughout the study the stubble height remaining plant tissue was set at 10 cm from the ground a height commonly used by Chaco cattlemen Ledesma 2006 Kunst personal observation Plant samples were transported to the lab and oven dried at 60 C for 48 h
18. con servative vegetation clearing approach Ledesma 2006 Kunst et al 2012 These yields present no practical difference with those reported for Green Panic growing in full sunlight in the Chaco region of Argentina ranging from 4 600 to 8 000 kg DM ha irrespective of harvesting interval Ricci et al 1997 De Leon et al 1995a De Leon 1999 The two peaks of growth observed have been also reported by De Leon 1999 for Green Panic growing under full light conditions in the Chaco region Ramirez Reynoso et al 2009 working with P maximum Mombaza in full light conditions with 1 000 mm of annual summer rainfall reported AGR of 66 140 kg DM ha day for cutting inter vals of 3 and 7 weeks respectively These magnitudes are within the range observed in this study The depression in BM observed between growth peaks in early mid summer January February is attributed to the fact that in the Chaco region January presents usually the highest annual air temperatures as the GDD pattern indicates Figs 2 3 4 5 6 suggesting an extreme water demand that Green panic was not able to withstand The final decline of the absolute growth rate at the end of the growth season could be attributed to lower air temperatures The lowest Green Panic annual yield was registered in the 02 03 season which also presented the largest rainfall amount This result could be attributed to the rather unusual rainfall pattern and the high evaporat
19. fallen The growth period of the species lasted from 6 to 7 months from mid late spring to early fall from October November to March April Figs 1 2 3 Green Panic did not grow during the rest of the year fall to late winter May to early October Irrespective of growth season the growth curve of Green Panic presented three phases separated by two peaks of AGR the initial phase which began in October early Decem ber and lasted to late December mid January a middle phase from mid January to mid February and a final phase lasting from late February to late March early April Figs 2 3 4 5 6 These two peaks of AGR were consistently identified despite harvesting intervals the first was observed at the end of December early January early summer an average of 50 days after the beginning of the sampling and the second from early February late March late summer early fall an average of 131 days after the beginning The first AGR A Springer 5 de 15 Fig 2 Aboveground biomass accumulation curve BM and absolute growth rate AGR of P maximum cv Trichoglume cv Petrie Green Panic for the 2000 01 season La Maria Experimental Ranch INTA Santiago del Estero Argentina References rainfall AGR and growing degree days GDD correspond to the time period between harvesting dates BM plot group 1 and BM plot group 2 are BM as estimated by the successive harvests approach and BM curve
20. he Richards function coefficient a varied between 3 500 and 12 237 DM ha Table 2 The R between the field and the estimated data was 0 98 although both functions used overesti mated BM toward the end of the growth season The coefficient C was almost constant in all growth models Table 2 The functional approach identified only one AGR peak as suggested by the inflection point of the curve and its location varied according to the growth season from 22 to 97 days since Y Springer day 0 Table 2 In the inflection point the magnitude of the calculated maximum growth rate was of similar magnitude of the first AGR peak in all growth seasons as calculated by the harvesting method Table 2 Growth season and harvesting interval significantly affected the relative growth rate p gt F 0 0015 and p gt F 0 0002 respectively while the interaction between harvesting frequency and growth season was not significant The mean relative growth rate of the 2001 02 season was higher than the mean relative growth rate of the 2002 03 season The 30 day harvesting period presented a mean relative growth rate twice as high as the mean relative growth rate of the 15 day harvesting period 1 820 versus 500 kg MS ha respectively p lt 0 05 Figs 5 6 The final accumulated BM of the 15 days harvesting interval was 39 42 less than the 30 day harvesting interval Figs 2 3 4 5 6 8 de 15 Sitio Argentino de Producci n
21. ion of the pad docks was a secondary forest with a homogeneous shrub stratum After the roller chopping treatment the vegetation structure consisted of an uneven age tree and brush stand with a mean distance between trees around 5 6 m resulting in a density of 200 300 trees per hectare Trees had an average height of 11 manda DBH larger than 10 cm Shrub mean height was around 3 5m The remaining mean total canopy ground cover of the trees was 75 while that of the shrubs was 35 visually estimated The tree stratum was dominated by the native hardwood species Aspidosperma quebracho blanco Schlecht quebracho blanco and Schinopsis lorentzii Griseb Engl que bracho colorado The first is an evergreen species that 2de15 SAICO Argentino de Froduccion Animal Agroforest Syst may reach a height of 20 m and a DBH of 80 cm while the latter may reach a height of 25 m and a DBH of 1 50 m Tortorelli 2009 Other tree species present were Zyzyphus mistol Griseb and Prosopis nigra Griseb Hyeron Shrub species present were Acacia furcatispina Burk Celtis spinosa Spreng and Capp aris atamisquea Kuntze Mean photon flux under the woody plant canopy during spring at noon at the ground 0 5 and 1 m height aboveground was 21 71 31 and 28 of the available flux at the same height in full sunlight respectively as estimated by the LI COR bar A 129 and measured at noon in summer Kunst unpublished information Field work Data
22. ira Brasilia 43 429 435 Carrillo J 2003 Manejo de pasturas Ediciones INTA Buenos Aires Casta ares M 2002 Curvas de crecimiento y calidad forrajera de Panicum maximum var Trichoglume cv Green Panic bajo cobertura arb rea en un ambiente rolado Graduate Thesis Facultad de Agronom a y Agroindustrias Uni versidad Nacional de Santiago del Estero Santiago del Estero Chacon Moreno E Rada F Sarmiento G 1995 Intercambio gaseoso nitr geno foliar y optimaci n en el manejo de Panicum maximum tipo com n sometido a diferentes frecuencias de corte Turrialba 45 19 26 Y Springer 13 de 15 Sitio Argentino de Producci n Animal Conover W 1980 Practical nonparametric statistics 2nd edn Wiley New York De Le n M 1999 Las pasturas subtropicales en la regi n semi rida central del pa s p 15 34 Simposio Internacional de Forrajeras Subtropicales Facultad de Agronom a y Zootecnia Universidad Nacional de Tucum n Tucum n De Le n M Peuser R Boetto G Luna G Bulaschevich M 1995a Efecto del genotipo y la frecuencia de defoliaci n sobre la producci n de materia seca en gram neas mega t rmicas cultivadas Rev Arg de Prod Anim 15 226 228 De Le n M Peuser R Boetto G Luna G Bulaschevich M 1995b Efecto de la frecuencia de defoliaci n y del genotipo y sobre la calidad del rebrote forraje producido en gram neas megat rmicas Rev Arg de Prod Anim 15 229 231 Durr F Rangel J 2000 The response of Panicum ma
23. ive demand of that season as suggested by the annual GDD The parameters of forage quality gathered in this study are quite similar to those reported for Green A Springer 9 de 15 SAICO Argentino de Froduccion Animal Agroforest Syst e to 15 cm depth a 15 to 30 cm depth To a 008 S 00S 00S TI 00L 9 00 L 1 24 WC 5 potsod Apn3s SULmp Wd paje nunoy oL 9p osenurs uoNeIg peownodxy 013184 ep 03enues youry piuownodxg New gT 0 2007 PU ZO 1007 10 0007 Suoseas YIMOIS y 10 YORoidde oy q PIJRUINSI sv I94A09 POOM I pun STUB U3913 Id AD IUIN SOYILA AD UNUIXDU UNID JO YOV p ey m o lt T lt Juajuodainjsiow LoS 6L8 ILL 069 899 68S ww yeod YOV puosas mun pezu pawpmuwnooy PWP TOOZ E0 TZ TOO7 E0 90 TOOZ ZO 6T TOO7 ZO0 vO Dates TOOZ TO 0Z Tooz T0 so o00z zT Tz o y81 rel Ec SII OL 0 Aep IDUIS skep JO Joquinyy 0007 71 90 AA JUB UODJB EM 10S OT mdy I Je Ie LZ A pl qx PpeArosqgo aqa de 15 to 30 cm depth fo 0 to 15 cm depth a Ti 8 0E 2981 08071 Sel eS 76 _Aep _ey WA 3 PILA yeod YOV PT COMPO LL TOEO tO EW EW Pl coe Pra un q EWEWLL m EW LO LE L0 Z1 8z AUTASI LO LL OE SOIS TEC YST CIC L91 wu yeod AOV 1511 mun eyurer paje numooy Oo a y 15 to 30 cm depth Oto 15 cm depth
24. lados en el Chaco semi rido In Arr oquy J Ledesma R Roldan Bernhard S G mez A eds Proc 02d Congreso Nacional de Sistemas Silvopastoriles INTA Santiago del Estero p 212 220 Anriquez A Albanesi A Silberman J Kunst C Suarez R Dom nguez Nu ez J 2012 Densidad aparente y materia org nica del suelo en rolados del Chaco Semi rido In Arroquy J Ledesma R Roldan Bernhard S G mez A eds Proc 2d Congreso Nacional de Sistemas Silvopas toriles INTA Santiago del Estero p 299 304 Anr quez A Albanesi A Kunst C Ledesma R L pez C Rodriguez Torresi Godoy J 2005 Rolado de fachinales y calidad de suelos en el Chaco occidental Argentina Ciencia del Suelo Argentina 23 145 157 Anslow R Green J 1967 The seasonal growth of pasture grasses J Agric Sci Camb 68 109 122 Araujo A 2003 Analysis of variance of primary data on plant growth analysis Pesqui agrop Brasileira Brasilia 38 1 10 Belsky A Mwonga S Duxbury J 1993 Effects of widely spaced trees and livestock grazing on understory environ ments in tropical savannas Agrofor Syst 24 1 20 Boletta P 1988 Clima Ch 1 p 7 15 In Desmonte y habilitaci n de tierras en la regi n Chaque a semi rida Oficina Regional de la FAO para America Latina y el Caribe Santiago Canto Weber do M Cabreira Jobim C Gasparino E Hoeschl A 2008 Caracteristicas do pasto e acumulo de forragem em capim tanzania submetido a alturas de manejo do pasto Pesqui Agrop Brasile
25. ll and soil moisture was also explored The information gathered was used to develop manage ment recommendations for Green Panic pastures growing under agroforestry systems in the Chaco region Materials and methods Study area It was located in the La Maria Experimental Ranch Santiago del Estero Experimental Station Instituto Nacional de Tecnologia Agropecuaria Santiago del Estero Argentina 28 3 S and 64 15 W The climate is semiarid subtropical Winter is cold and dry and summer is warm and rainy Boletta 1988 The mean annual precipitation is 574 mm Meteorological Sta tion INTA Santiago del Estero Experimental Station 1990 2008 series occurring mainly from late October to early May Boletta 1988 INTA Meteorological Station Santiago del Estero Experimental Station unpublished report Soils are Entic Haplustols the most frequent suborder in the western Chaco region Anriquez et al 2005 Main characteristic of the soil profile is an organic matter content of 2 3 and a high drainage rate due to the dominance of the silt fraction in its texture Santiago del Estero Experi mental Station unpublished report Permanent wilt ing point PWP of the soils of the experimental area is around 6 7 Lorenz Personal communication The experimental material was Green Panic seeded by hand after the roller chopper treatment in 1996 and 1997 of two 10 ha paddocks located in a highland ecological site The original vegetat
26. lyzed for crude protein and acid detergent fiber after sample Y Springer Agroforest Syst grinding in a Wiley mill milling and screening through a 1 mm mesh Crude protein content was estimated by the Kjeldahl method Acid detergent fiber was esti mated by the Van Soest method Castanares 2002 For the 2000 01 and 2001 02 growth seasons the leaf shoot ratio of each sample was calculated and averaged for each harvesting periods and sampling dates and plotted versus time to assess its behavior Mathematical and statistical analysis Growth features of Green panic were estimated using two approaches a the harvesting method Anslow and Green 1967 and b the functional approach Hunt 1982 In the first method the mean standing BM of Green Panic was calculated for each sampling date plot group and growth season In a second step a curve of mean accumulated BM was determined by summing up the successive BM observed until a specific date The magnitude of the rate of BM between two harvesting dates an estimation of the mean absolute growth rate AGR of the species was estimated by calculating the difference of the mean accumulated BM between sampling dates t and t divided by the interval of time between these dates expressed in days Hunt 1982 formula 2 AGRni kg DM ha day BM BM tn 1 th 2 where BM 1s the aboveground biomass harvested at the sampling date t 1 BM the aboveground bio
27. mass harvested in the sampling date t and h harvesting period 1 and 2 and i plots 1 to n Accumulated BM and AGR were plotted versus time to assess its annual pattern The functional approach was applied by fitting growth models to the accumulated BM curves classi fied by growth season and harvesting interval by non linear regression Hunt 1982 For the 2000 01 season the Richards function Hunt 1982 presented the lowest mean square error and was selected as the best equation to model the accumulated BM curve throughout time formula 3 d ABM a 1 exp Cav 3 where ABM is the accumulated aboveground grass biomass kg DM ha a is the coefficient represent ing the maximum grass productivity kg DM ha b 4de 15 Sitio Argentino de Producci n Animal Agroforest Syst is the starting value kg DM ha C the intrinsic rate of increase representing an average growth rate per c pita of the dry matter kg DM ha day C could be interpreted as an average AGR that ignore short term fluctuations of the environmental parame ters The coefficient d controls whether or not the function has an inflection and 1f so where 1t occurs Tsoularis and Wallace 2002 For the 2001 2002 and 2002 2003 seasons and for each harvesting frequency a three parameter logistic growth function presented the lowest mean square error and was selected to model the dynamics of ABM throughout time formula 4 Overma
28. n and Scholtz II 2002 ABM a 1 bexp J 4 with all parameters as above The parameters of Eqs 3 4 were estimated using the package INFOSTAT INFOSTAT 2008 that uses the simplex and or the Levenberg Marquardt methods to estimate equation coefficients The pattern of the absolute growth rate and the location of the inflection point of the accumulated BM curves were used to identify the pattern of increase and decrease of growth rate throughout time and used as an indication to define periods of grazing and rest of P maximum The inflection point of a curve is the point when its curvature changes sign and the growth rate is maximum Tsoularis and Wallace 2002 Time to inflection and the maximum growth rate observed at the time of inflection for the Richards and logistic equations were calculated using formulas provided by Tsoularis and Wallace 2002 Differences in the relative growth rate between the two harvests were tested using a two way random ANOVA with In transformed BM collected in each sampling date as dependent variable and growth season classification factor n 2 2001 02 and 2002 03 harvesting interval treatment n 2 15 and 30 days respectively and their interaction as independent variables using a repeated measures approach Araujo 2003 Ramirez Reynoso et al 2009 The model had no intercept Each plot was considered a replication for a treatment n 4 by harvesting date Conceptually har
29. nt vegetation of the Chaco Morello and Adamoli 1974 Concurrently its suitability for livestock oper ations has decreased The conversion of a woodland shrub thicket or a dense secondary forest in a vegetation type more fitted for livestock operations is approached in the region by roller chopping This A Springer 1 de 15 Sitio Argentino de Producci n Animal mechanical treatment crushes the woody under growth creating a park like structure and enhancing accessibility of both livestock and personnel Trees with diameter at breast height DBH larger than 10 15 cm and tall shrubs are left standing so a roller chopped paddock is characterized by a reduction of sunlight availability if compared with treeless pas tures Standing forage and stocking rate are increased by the sowing of grass instantaneously with the roller chopping treatment Kunst et al 2003 Species of the genus Panicum are commonly used being P maxi mum Jacq cv trichoglume cv Petrie locally referred as Green panic one of the species of choice Green panic possess the C4 photosynthetic process it is a summer perennial and has a high nutritional quality and yield potential Moreno et al 1995 It is indigenous to tropical areas of southern Africa where it occurs mainly in the subhabitat under the trees Pieterse et al 1997 Concerns about the sustainability of the Chaco ecosystem favor vegetation clearing methods that retain native tree
30. ntroladas Nota T cnica Pas tos y Forrajes Cuba 24 305 Pieterse P Rethman N Van Bosch J 1997 Production water use efficiency and quality of four cultivars of Panicum maximum at different levels of nitrogen fertilization Trop Grass 31 117 123 Ramirez Reynoso O Hernandez Garay A Carneiro Da Silva S Perez Perez J Enriquez Quiroz J Quero Carrillo A Herrera Haro G Cervantes Nu ez A 2009 Acumulaci n de for raje crecimiento y caracteristicas del pasto Mombaza Panicum maximum Jacq cosechado a diferentes inter valos de corte T c Pec en M xico 47 203 213 Reese P 1993 Overlooked and neglected principles of grazing management Proceedings the range beef cow symposium XII University of Nebraska Lincoln Consulted in Sep tember 2013 digitalcommons unl edu rangebeefcowsymp 226 Ricci H Guzman L Perez P Juarez V Diaz A 1997 Pro ducci n de materia seca de siete gram neas tropicales bajo tres frecuencias de corte CIAT Colombia Pasturas Tropicales 19 45 49 14 de 15 Sitio Argentino de Producci n Animal Agroforest Syst Santos Menezes P Alvares Balsalobre A Corsi M 2003 Morphogenetic characteristics and management of Tan zania grass Pesqui agrop brasileira Brasilia 38 991 997 SAS 1998 Release vol 6 12 SAS Institute Cary Smart A Dunn B Johnson P Xu L Gates R 2007 Using weather data to explain herbage yield on three Great Plains communities Range Ecol Manag 60 146 153 Smit G 2005 Tree
31. thinning as an option to increase herbaceous yield of an encroached semi arid savanna in South Africa BioMed Central BMC Ecology 5 1 15 Tavares de Castro C Garcia R Mesquita Carvalho M Couto L 1999 Producao forageira de gramineas cultivadas sob luminosidade reduzida Rev bras zoot 28 919 927 Tortorelli L 2009 Maderas y bosques argentinos 2 edici n Orientaci n Grafica Editora Treydte A Heitkonig T Prins H Ludwig F 2007 Trees improve grass quality for herbivores in African savamnas Perspect Plant Ecol Evol Syst 8 197 205 Tsoularis A Wallace J 2002 Analysis of logistic growth models Math Bios 179 21 55 Vallentine J 2001 Grazing management Academic Press San Diego p 579 A Springer 15 de 15
32. uired to maintain exponential growth and to produce biomass 1 e forage Groene veld 1998 Carrillo 2003 Santos et al 2003 Since the leaf area is reduced frequent cuttings cause a decrease in tiller production thus the ability of a plant to replenish reserves or produce additional new tillers is restricted Plants cut near the ground rely on basal buds to recover instead of aerial buds located in tillers a process that takes some time Chacon Moreno et al 1995 The increase in the leaf shoot ratio toward the end of the growth season in Green Panic showed in this study also suggest a deleterious effect in tillering caused most likely by the frequent cutting The soil moisture failed as a predictor of BM as indicated by the lack of significance of the correla tion between its time series This result has been reported in other studies of grass yield soil moisture relationships Smart et al 2007 and could be attributed to the inherent high drainage of the soils of the study area and also to the lack of adjusted timing between the sampling schedule and the rainfall occurrence Management implications Although the growth pattern of Green Panic followed the weather pattern as the native species do the maximum expected aboveground production for Green Panic under woody cover shadow estimated for a silvopasture created by roller chopping and with 20 30 of photon flux was quite similar to Green Panic growing under full sunlight
33. v Petrie Green Panic a by p gt hl 0 03 growth season and b by 0203 Rainfall between sampling dates T 0 62 growth season sorted by p gt hl 0 0034 harvesting intervals 2001 02 and 2002 03 Growing degree days T 0 72 p gt il 0 0006 B Growth season Environmental variables HIIS HI30 01 02 Rainfall between sampling dates T 0 42 0 73 p gt htl 0 07 0 04 Growing degree days T 0 38 0 47 p gt rl 0 10 0 18 02 03 Rainfall between sampling dates T 0 44 0 66 p gt ltl 0 095 0 17 References HI15 15 day Growing degree days T 0 55 1 00 harvesting interval HI30 p gt 0 04 0 04 30 day harvesting interval Acknowledgments Research was supported by the Instituto Nacional de Tecnolog a Agropecuaria INTA through Specific Research Project Desarrollo de sistemas silvopastoriles and INTA Tucuman Santiago del Estero Regional Center Research and Extension Project Intensificaci n de la Producci n de Carne Bovina del Noroeste Argentino 1999 2004 We would like to thank Dr Hugh Dove CSIRO Australia for its suggestions that greatly improved this manuscript References Albanesi A 2012 Suelos en sistemas silvopastoriles de la regi n chaque a In Arroquy J Ledesma R Roldan Bernhard S G mez A eds Proc 2nd Congreso Nacional de Sistemas Silvopastoriles INTA Santiago del Estero p 212 220 Albanesi A Anriquez A Silberman J Kunst C Duffau A Dominguez Nu ez J 2012 Fracciones de carbono org nico del suelo en ro
34. ve 28 Dec 01 SS 17 Dec 01 Q 15 Nov 01 of 0 5 Nov 01 as 30 y days Harvesting interval Fig 8 Leaf shoot relationship of P maximum cv Trichoglume cy Petrie Green Panic under woody plant canopy in a roller chopper treatment for two harvesting regimes 2001 02 season La Maria Experimental Ranch Santiago del Estero Experimen tal Station Argentina harvest In full sunlight environments it has been reported a negative association between the magnitude of the absolute growth rate and a high cutting frequency while a positive increasing trend in the yield of Panicum species as the harvesting interval increases Moreno et al 1995 Gonzalez et al 1997 De Le n et al 1995b Ricci et al 1997 De Le n 1999 Ramirez Reynoso et al 2009 The compensatory responses to tissue removal i e the magnitude of AGR after each cut in our study seems were not enough to maintain a high rate of BM accumulation when the harvesting interval was 15 days Low stubble heights as used in this study could be also the cause of the small magnitude of the second AGR peak Higher stubble heights larger than 20 cm are associated to higher aboveground biomass yields in Panicum species do Canto Weber et al 2008 Ramirez Reynoso et al 2009 Kiss Trocsanyi et al 2009 The production of tillers is one of the main phases of vegetative grass growth if this process is affected the final productivity will suffer a reduction since tillering is req
35. vesting intervals represent grazing intensities while growth seasons represent different weather environments The PROC MIXED procedure of the SAS package SAS 1998 Littell et al 1998 was used for calculations Differences in the mean relative growth rate among growth seasons and harvesting frequencies were tested using the LSMEANS statement SAS 1998 An 0 05 was used for all statistical analysis We used the Kendall s t a non parametric corre lation coefficient Conover 1980 to assess the rela tionships between the time series of the mean accumulated BM with the time series of SMIS SM30 and the rainfall amount and GDD observed between sampling dates for each growth season and harvesting period The Kendall coefficient was used because the relationship among these variables was expected to be monotonic but not linear Conover 1980 To assess any delay in plant response the time series were lagged one sampling date Khan 1971 Gibbens 1991 Statistical significance was assumed at p lt 0 05 The PROC CORR procedure of the SAS package was used for calculations SAS 1998 Results Growth features In the three growth seasons assessed the plants of Green Panic started to grow with 30 40 mm of monthly accumulated rainfall and a GDD above 150 C Growth slowed and eventually stopped when the GDD between harvesting dates was less than 100 C and air temper atures fell under 15 C irrespective of the amount of rainfall
36. ximum to a simulated subcanopy environment I Soil x shade inter action Trop Grass 34 110 177 Eriksen F Whitney S 1981 Effects of light intensity on growth of some tropical forage species I Interaction of light intensity and nitrogen fertilization on six forage grasses Agrofor J 73 427 433 Gibbens R 1991 Some effects of precipitation patterns on mesa dropseed phenology J Range Manag 44 86 90 Gillen J McNew R 1987 Seasonal growth rates of tallgrass prairie after clipping J Range Manag 40 342 345 Gomez de la Fuente E Diaz Solis H Saldivar Fitzmaurice A Briones Encinia F Vargas Tristan V Grant W 2007 Patron de crecimiento de pasto buffel Pennisetum ciliare Link Sin Cenchrus ciliaris en Tamaulipas M xico Tec Pec en M xico 45 1 17 Gonzalez R Delgado H Faria M rmol D Morillo D 1997 Evaluaci n de cultivos puros y asociados de Panicum maximum y Centrosema sp Interrelacionados con frecu encias de corte Archivos Latinoamericanos de Producci n Animal Suplemento 1 63 65 Groeneveld H 1998 Measuring the RGR of individual grass plants Ann Bot 82 803 808 Hunt R 1982 Plant growth curves The functional approach to plant growth analysis University Park Press Baltimore p 249 Infostat 2008 InfoStat versi n 2008 Manual del Usuario 1st edn Grupo InfoStat Universidad Nacional de C rdoba Facultad de Ciencias Agrarias C rdoba Ivory D Whiteman P 1978 Effect of temperature on growth of five subtropic

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