Optimum Leaf Area Index to Reach Soybean Yield Potential in Subtropical Environment

The interactive influence of climate and management factors on leaf area index (LAI) of soybean yield potential has not been investigated in subtropical environments. Such information can help in optimizing current soybean management practices to increase seed yield and efficiency of resource use. The objective of this study was to identify the optimum leaf area index for attaining yield potential in modern soybean cultivars grown in a subtropical environment. A large soybean yield, LAI, and phenology database collected from a combination of on-farm and research-station experiments conducted during four soybean growing seasons (2011-2015) in southern Brazil was used. The database represented a wide range of weather conditions, soil types, sowing dates, and cultivar maturity groups (MGs). A boundary function was derived for the relationship between soybean yield and LAI at R1 and R5 developmental stages for cultivars of determinate and indeterminate growth habit, and for both types combined. An increase in yield was in line with the increase of LAI for experiments with a small yield gap (soybean yield more than 4.5 Mg ha(-1)). In this case, optimum LAI at R1 growth stage (LAIR1, opt) to reach the soybean yield potential was between 3.4 (indeterminate) and 4.5 (determinate) whereas the optimal maximum LAI (LAI(max, opt)) is between 6.0 and 6.5 for indeterminate and determinate cultivars, respectively. These results suggested that management practices for soybean crops that involve the LAI and high yield potential must be adjusted according to the maturity group, growth habit and sowing date in a subtropical environment.