Climate and Management Factors Influence Soybean Yield Potential in a Subtropical Environment

The interactive influence of climate and management factors on soybean [Glycine max (L.) Merr.] yield potential has not been investigated in subtropical production environments. Such information can help fine tune current soybean management practices to increase yield and resource-use efficiency and to minimize risk. The objective of this study was to identify key biophysical and management factors governing variation in soybean yield potential in southern Brazil. To accomplish that objective, we used a large database on soybean yield and phenology collected from a combination of on-farm and research-station experiments conducted during four crop growing seasons (20112015) in Rio Grande do Sul (southern Brazil). The database portrayed a wide range of weather conditions, soil types, water regimes, sowing dates, and cultivar maturity groups (MGs). Water supply and photothermal quotient explained most of yield variation across site-years. A boundary function was derived for the relationship between soybean yield and water supply, and an attainable water productivity of 9.1 kg grain ha(-1) mm(-1). A seasonal water supply of similar to 800 mm appeared sufficient to maximize seed yield, and most late-sown crops fell short of this value. Late-sown crops were also exposed to a lower photothermal quotient during reproductive stages, and this explained the yield penalty of 26 kg ha(-1) d(-1) of sowing delay after 4 November observed for non-water-limited crops. Sowing date, accompanied by proper selection of cultivar MG and determination of soil water status at sowing time, appear to be the most cost-effective management practices to ensure a high photothermal quotient and low risk of water deficit during reproductive stages and, therefore, a high yield potential in the subtropical environment of southern Brazil.