Conserved water use improves the yield performance of soybean (Glycine max (L.) Merr.) under drought

We evaluated the importance of conserved water use in drought adaptation in soybean [Glycine max (L.) Merr.], and identified the traits involved in this mechanism. Eight soybean genotypes, four landraces and four recent cultivars, were collected and yield performance in the field was determined and used in pot experiments to evaluate the yield performance and the water use pattern under three soil moisture treatments imposed from 40 days after sowing: well-watered [WW, soil water content (SWC) maintained between 85%–100% field capacity (FC)]; water stress (WS, water withheld until SWC decreased to 30% FC, rewatered to 100% FC and water withheld again to 30% FC); and terminal water stress (TWS, water withheld until maturity). The recent cultivars all out-yielded the landraces in two different years in the field and under well-watered conditions in the pot experiment. Among the eight soybean genotypes, J19 and ZH – two recent cultivars with lower daily water use before flowering, but higher use after flowering – had the best yield performance in the WS and TWS treatments in the pot experiment and in the field. These two soybean genotypes and J19, another recent cultivar, had higher grain yield, hundred-grain weights and water use efficiency for grain yield (WUE_G) in the WS treatments than the other genotypes, and higher hundred grain weights, higher WUE_G, higher pod numbers and the only significant grain yield in the TWS treatment. J19 and ZH had low root length densities (RLD), low leaf areas at flowering, and transpiration decreased at high plant available soil water content under drought. Thus, we conclude that reducing RLD and restricting water loss contributed to conserved water use and improved yield performance and WUE_G in water-limited conditions.