Physiological and yield responses of soybean under water deficit

Water deficit during grain filling is a key factor on soybean ( Glycine max (L.) Merrill) production, but plant response to different water stress levels should be better understood. This study evaluated soybean plant response to different soil water levels during grain filling. It was assessed the gravimetrical humidity and soil matric potential, leaf relative water content, leaf water potential, proline, and yield components of plants under a range of days without irrigation (0, 3, 6, 9, and 12) during grain filling phase. Until soil matric potential was around −0.8 atm soybean water deficit tolerance mechanisms were enough to maintain leaf relative water content and leaf water potential at acceptable levels, which proline concentration was a key factor in this mechanism. Leaf relative water content and leaf water potential showed to be related in maintaining soybean yield under water deficit and they may be used in studies of soybean tolerant cultivars to water restriction. From 9 days on, critical yield losses were observed due to water stress. The information presented in this study supports soybean producers in decision-making in irrigated systems to minimize productivity losses due to water deficit during the critical period of the crop–grain filling.