ICRISAT Archival Report 2006 - The seedlings of success in the ...

9A.4 Simulating Cereal Legume Rotations in southern Africa
Bongani Ncube, John P Dimes, Mark T van Wijk, Steve J Twomlow; Ken E Giller – ICRISAT and Wageningnen
Agricultural University
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Total Biomass
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Grain
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ICPL
87091
ICEAP
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86D 719 CBC1 Natal
Common
Nyanda
Sorghum
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ICPL
87091
ICEAP
00535
86D 719 CBC1 Natal
Common
Nyanda
Sorghum
Figure 9A.5. Observed and predicted total biomass and grain yield of legumes across three cropping seasons at Lucydale.
Error bars represent standard errors of the means of the yields. Sorghum failed to establish in 2003/2004.
We assessed how accurately the APSIM model can predict observed legume and rotation sorghum yield and how the
model can assist in explaining the mechanism of the residual benefit of legumes to sorghum under dry semi-arid
conditions. The model was used to simulate the measured soil and plant responses in a legume-sorghum rotation
experiment conducted at Lucydale, Matopos Research Station in south-western Zimbabwe, between 2002 and 2005
Local climate, measured soil mineral N, soil organic matter (SOC) and water data were used as inputs to the model.
Sequences of cowpea (Vigna unguiculata (L.) Walp), pigeonpea (Cajanus cajan (L.) Millsp.), groundnut (Arachis
hypogaea L.) and sorghum (Sorghum bicolor (L.) Moench) were used to simulate the rotations. Existing parameters
in the model for cowpea, pigeonpea and sorghum were found to capture the observed phenology and grain
partitioning of the experimental cultivars reasonably well. In the case of groundnut, new cultivar parameters were
constructed and calibrated using the observed harvest index and flowering data. APSIM predicted total biomass and
grain yields of the legume phase well. Sorghum yield was also predicted well in rotation after cowpea and
groundnut, but the model under-predicted sorghum yield after pigeonpea and after sorghum in 2004/05 (Figure
9A.5). The under-predictions were probably due to the exclusion of leaf fall in pigeonpea, and an under-estimation
of soil N mineralization in the case of sorghum. Model output on sorghum N and water stresses indicated that the
legume-cereal rotation is more driven by soil nitrogen availability than water availability even under semi-arid
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