Responses of soybean to water stress and supplemental irrigation in upper Indo-Gangetic plain: Field experiment and modeling approach

Understanding better the impacts of extreme dry spell regimes is essential for optimizing water management under a changing and variable climate. Using field experiments and modeling studies, we examined the impacts of dry spells in soybean and identified better management of water resources under varying water-scarce conditions. Field experimental data from soybean (PUSA-2614) experiments (July-Oct 2014; IARI, New Delhi, India) were used to calibrate and validate InfoCrop-Soybean model. This model was used to simulate optimal timing of irrigation under different dry spell scenarios. Results showed that plants subjected to water stress during flowering and vegetative growth stages had significantly lower yields and total dry matter (TDM). Supplemental irrigation significantly increased TDM and yields. InfoCrop-Soybean could simulate plant responses to water stress, at various stages of crop growth, and to supplemental irrigation, with acceptable accuracy. The crop model was further used to simulate impacts of dry spells at different intensities and durations on soybean growth and yields by creating drought scenarios for the New Delhi region using 36 years of weather data (1978-2014). Simulations showed that a 20% reduction in rainfall during any fortnight (every 15th day) of the cropping season does not affect crop yield significantly. However, dry spells (50% reduction in rainfall or more) in August and early September led to reduced yields, while supplemental irrigation during those dry spells could reduce yield losses. We envisage that the results of this study can help better manage water in soybean cultivation under dryland condition.