Identifying the most sensitive growth stages of soybean to defoliation

Identifying sensitive plant growth stages is vital for effective crop management. Defoliations is a widely used technique to assess the crop sensitivity to decreased assimilate supply in many crops including soybean [Glycine max (L.) Merrill]. Previous studies suggest that soybean is vulnerable to defoliations across different growth stages. However, the most sensitive soybean growth stage to defoliation is not clearly understood as previous studies have tested the effect of defoliation at one or few growth stages. Hence, this study was conducted with defoliations (67% leaf removal) across different soybean growth stages between vegetative stage (V4) to physiological maturity (R7) using two soybean cultivars from different maturity groups. Defoliation at most growth stages reduced soybean yield parameters, with the greatest reduction occurring during the early seed development stages (R5 to R5 + 1 week). The results from this study suggest that the early seed development stage is the most sensitive stage to defoliation induced assimilate limitations in soybean. Therefore, avoiding stresses which limit photoassimilates availability particularly during early seed-filling stage, is critical for maintaining soybean productivity.