Environment quality, sowing date, and genotype determine soybean yields in the Argentinean Gran Chaco

Abstract

The Argentinean Gran Chaco is one of the global regions with the highest recent rates of agricultural expansion due to soybean production. The area has been heavily deforested during the last 30 years. Despite the economic relevance of soybean for this region, studies that provide options for sustainable management of these production systems are scarce. The objectives of this study were (i) to identify and to quantify key management and environmental soybean yield predictors, and (ii) to explore interactions with maturity group (MG) selection, since farmers are sowing genotypes ranging from MGs V to VIII. We evaluated commercial genotypes in 112 multi-environment on-farm trials (METs) consisting of 14–19 genotypes each during 11 consecutive years (from 2008 to 2019). We first analyzed a single genotype sown in 106 METs to identify environmental and management yield predictors with good explanatory power for yield, which ranged from 435 to 5117 kg ha−1. Relevant environmental variables were, in order of importance, rainfall from 30 days before sowing to physiological maturity (R7), years after land conversion to agriculture, reference evapotranspiration from sowing to R7, and the number of 2-day periods with maximum temperatures above 35 °C from beginning of flowering (R1) to R7. Based on variable relative importance (RI) sowing date was the most important management variable (RI = 0.99), followed by phosphorous availability (RI = 0.59). Genotype selection also had a strong significant effect. There was an interaction between MG and sowing date, yield reductions with delayed sowings ranked as MG VIII > VII > VI = V. The largest yield differences between MGs were observed under environments with high soil organic matter (explored range from 1.64 to 4.05 %). These results illustrate specific management variables to guide farmers and advisors to optimize regional soybean cropping systems. The negative yield effect promoted by years after land conversion and reductions in soil organic matter suggest a decline in the environmental quality of the region and the need for new production alternatives to halt these trends.