Modelling management strategies for wheat–soybean double crops in the south-eastern Pampas

J.P. MONZON; V.O. SADRAS; P.A. ABBATE; O.P. CAVIGLIA

FIELD CROPS RESEARCH

ELSEVIER SCIENCE BV

Año: 2007 vol. 101 p. 44 - 52

0378-4290

Favourable conditions in the last years have stimulated the adoption of wheat-soybean double crops in the south-eastern Pampas, but the long-term performance of this strategy is largely unknown. Our aim was to assess the production of wheat-soybean double crops under contrasting management practices and weather scenarios at Balcarce (37.8 oS, 58.3 ºW). We used models CERES-Wheat and CROPGRO-Soybean with modifications in inputs and parameters to account for specific conditions in wheat-soybean double crops. Models were calibrated, and tests against independent data showed an acceptable capacity to reproduce the actual phenology and yield of wheat and soybean in double cropping systems. The models and long-term weather data were used to analyse management practices allowing for earlier soybean sowing, including: i) short-season wheat cultivars; ii) non-selective herbicides for faster drying of wheat before harvest, and iii) relay double cropping, where soybean is sown on standing wheat before crop maturity in contrast to sequential cropping where soybean is sown after wheat harvest. Impacts of soybean cultivars and soil depth on yields were also investigated. Advancing wheat harvest with herbicides and using early wheat varieties had little impact on soybean yield, but simulations assuming a hypothetical frost resistant wheat allowing for earlier wheat sowing and harvest indicated (i) wheat yields were maintained, and (ii) yield of sequential soybean increased 23% due to greater amount of remaining soil water and earlier sowing. Shallow soil reduced soybean yields, with no impact on wheat yields. Average soybean yield increased from 1738 kg ha-1 in sequential to 2099 kg ha-1 in relay cropping, whereas wheat yield was similar in both cropping approaches. Our modelling study indicated relevant seasonal variability in rainfall and yield that could be partially accounted by Southern Oscillation Index (SOI) and long-term trends in crop phenology and yield that could be associated with increased mean temperature. The amount of rainfall during the period of yield generation in wheat (20 October to 10 December) and the remaining soil water at the end of the wheat growing season were higher during Consistently Negative (CN) SOI phase, and lower during Consistently Positive (CP) phase in September. In the period between 1971 and 2003 average October-December temperature increased at 0.038ºC year-1. Higher temperature accounted for faster wheat development and earlier harvest (0.15 day year-1) with no impact on yield; this allowed for earlier sowing of double cropped soybean, which together with more favourable temperature lead to increases in simulated soybean yield at a rate of 26.2 kg ha-1 year-1.