Exploring avenues for tropical soybean intensification: how much water and nutrients are demanded to achieve exploitable yield?

Abstract

The world population is expected to rise by two billion in a few decades, boosting demand for soybean (Glycine max L.). Brazil has the world’s largest tropical agricultural area, accounting for 40 % of the world’s soybean output. This study was conducted to understand the potential and limitations of tropical soybean yield, estimate the amounts of main inputs (water and nutrients), and assess management to reach the crop yield potential (YP). We used CROPGRO-Soybean model, based on well-conducted experiments in different locations in Brazil. We generated estimates of YP and water-limited crop yield potential (YP-W), and explored long-term scenarios to evaluate the impact of sustainable practices on water management. Yield gap (YG) and agricultural efficiency (EA) were computed based on simulations and actual yield. The total water and nutrients required to achieve the YP in Brazil were also calculated. According to our simulations, YP ranged from 3,952 to 6,084 kg ha–1; YP-W from 3,133 to 5,186 kg ha–1, and YG from 589 to 4,401 kg ha–1. On average, drought stress negatively affected 14 % of YP, while 42 % of YP was lost due to management failures. Irrigation was needed in 26 % of the soybean-planted areas in Brazil to mitigate the risks associated to seasonal rainfall variations. Our findings revealed that it was possible to save around 20 % of the water through conservative soil practices and 25.0 106 Mg of macronutrients (N = 356 kg ha–1, P = 31 kg ha–1, K = 104 kg ha–1) annually is required to reach the exploitable soybean yield.