Deregibus, V. A.

Druille, M.

Garbulsky, M. F.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings 21st International Grassland Congress / 8th International Rangeland Congress Modeling the Growth of Alfalfa (Medicago sativa) in the Pampas Region M. Druille Universidad de Buenos Aries, Argentina M. F. Garbulsky Universidad de Buenos Aries, Argentina V. A. Deregibus Universidad de Buenos Aries, Argentina Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Plant Sciences Commons, and the Soil Science Commons This document is available at https://uknowledge.uky.edu/igc/21/1-2/23 The 21st International Grassland Congress / 8th International Rangeland Congress took place in Hohhot, China from June 29 through July 5, 2008. Proceedings edited by Organizing Committee of 2008 IGC/IRC Conference Published by Guangdong People's Publishing House This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. 瞯 ]72　 瞯 　 Multifunctional Grasslands in a Changing World 　 Volume Ⅰ 　Grasslands/Rangelands Resources and Ecology ——— Ecology of Grasslands/RangelandsModeling the growth of alfalfa (Medicago sativa) in the Pampas regionDruille , M . , Garbulsky , M .F . , Deregibus , V .A . Dep t . A nimal Production . Facultad de A g ronomí a . Universidad deBuenos A ires . A rgentina . E‐mail : druille＠ agro .uba .arKey words : lucerne , primary productivity , incident radiation , actual evapotranspirationIntroduction Carrying capacity of grazing systems on the Pampas ( Argentina ) and its secondary production depend on theaboveground net primary productivity ( ANPP ) of their forage resources . While there is descriptive information about theseasonal variability in the productivity of grown perennial forage species , there is less information about the environmentalcontrols of this variability from a long time series and spatially well distributed in the region . Among the cultivated species , thealfalfa ( Medicago sativ a) is the most important forage legume because the large sown area and the wide environmental gradientit occupies . Simulation models that allow estimating crop grow th have been developed for various parts of the world ( McCownet al . , １９９６) . The objective of this study was to construct a model to estimate the PPNA for this species , from local soil andclimate data .Materials and methods We used data from biomass harvests from a three‐year crop network test ( Chamber of Seed T raders‐CSBC) , located at different sites in the Argentine Pampa and for ７ years (１９９６ － ２００３ ) . We averaged for each month the dailyPPNA , calculated from the aboveground biomass accumulated between successive cuts . We worked with the information offour experimental sites located between ３１° and ３７° south latitude and ５９° and ６３° west longitude and covering an mean annualtemperature ranges from １３ .６ ℃ to １８ .４ ℃ and annual precipitation from ８４０ mm to １１２３ mm . Out of a total of ３１６ cuts , cutsfor the establishment phase and those periods of low grow th rates were eliminated . The monthly ANPP were correlated ,through multiple regressions , with the average monthly temperature , precipitation , incident radiation ( Rad ) and actualevapotranspiration ( ET r) . The latter was estimated from the above variables and data such as soil field capacity and wiltingpoint . We evaluated the best model developed with information from the northern location , using the data from that location isnot taken into account for the construction of the model and those for the other three seats , for its validation .Results and discussion The model that best explained the PPNA includes Rad and ET r [ mean monthly daily ANPP ( kg DM /ha .day) ＝ ４ .２４ 倡 Rad ＋ ４ .７１ 倡 ETr － ８ .９３ ] . The application of this model for the whole dataset showed a good agreementagainst the measured ANPP ( Figure １ ) . Overall , the model presented a satisfactory adjustment for all the analyzed locations( Figure ２) . The slope of the relationship between estimated and measured by cuts was not significant different to the line １ :１( p ＝ ０ .９２) . This model does not include ANPP monthly values that exceed ７０ Kg DM / ha .day , believing that these valueswould be explained by factors not taken into account in the design of the model , such as soil fertility or structural variables ofcultivation .　 Figure 1 Seasonal dynamics o f the A N PP ( 2000 /2003) , f or two contrasting sites : ( a) Raf aela and (b)Cnel . Suárez . Figure 2 Relationship between the measured and theestimated by the model A N PP f or the f our sites .Full line is the regression line and the dashed line isthe 1 :1 relationship .Conclusions Our results suggest that it is possible to estimate the ANPP from climatic data for a wide range of conditions in theArgentinean Pampas . The model could help to better understand the controls of ANPP and to make a more accurateplanification of stocking rate in grazing systems . Moreover , it could help to estimate the effects of climate changes on theANPP of alfalfa .ReferenceMcCown R . L . , Hammer G . L . , Hargreaves J . N . G . , Holzworth D . P . & Freebairn D . M . , １９９６ . APSIM : a NovelSoftware System for Model Development , Model Testing and Simulation in Agricultural Systems Research . A griculturalSystems ５０ : ２５５‐２７１ .(a) (b) ~ 70 ♦• ... •.: 110 110 R2 = 0.73 'C 60 ·-· 100 - - Estimated ANFP 100 Estimated Ar-PP .; ♦ .1:.• ♦ # • I RMSE = 9.74 00 -Measured ANFP 00 - Measured .ANPP .c ~ ~ ill 50 80 80 :ii ,, ,, ~ ~ 70 "' 70 40 . .c .c :E 60 :E 60 II. 0 0 II. 30 Cl 60 Cl 50 z . £ £ c( . : . 0. 40 0. 40 'C 20 . 0. 0. I!! z 30 z 30 :, 3: .;• .. ♦ < 20 < 20 !l 10 10 10 :ii / 0 0 0 10 20 30 40 50 60 70 Estimated ANPP (KgMS/ha day) 

Modeling the Growth of Alfalfa (\u3cem\u3eMedicago sativa\u3c/em\u3e) in the Pampas Region

https://uknowledge.uky.edu/cgi/viewcontent.cgi?article=2265&amp;context=igc

Modeling the Growth of Alfalfa (\u3cem\u3eMedicago sativa\u3c/em\u3e) in the Pampas Region

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