The effects of rainfall and irrigation on cherry root water uptake under drip irrigation

Studying the effects of rainfall and irrigation water on spatiotemporal variability of root water uptake are critical for understanding water utilization processes by plants and their importance in hydrological ecosystem functions. In this study, the spatiotemporal patterns of δ18O in soil water in the soil profile and proportion of root water uptake from different soil depths and irrigation water under three irrigation treatments (T1, T2 and T3, i.e. 70%, 85% and 100% of design irrigation quota) were analyzed during the growth period by detecting the stable hydrogen and oxygen isotopes (δD and δ18O) of soil water, xylem sap, rainfall and irrigation water (local groundwater) in a cherry orchard under drip irrigation during 2015-2016. Results showed that mean δ18O value of soil water in the profile was strongly linked with seasonal variation of soil water content, and was positively correlated with irrigation quota. Rainfall and irrigation promoted significant cherry root access to soil water at shallower depths. With the growth of cherries came changes in the proportion of water sources. Initially, root water uptake was mainly from the middle soil layer (20-50 cm), then topsoil (0-20 cm), and finally the deep soil layer (50-100 cm). The contribution of irrigation water to root water uptake decreased from the postharvest stage, and the effect of irrigation amount on improving the contribution of irrigation water to root water uptake also declined greatly. Therefore, based on comprehensive consideration of the patterns of cherry water uptake and rainfall characteristics during the cherry growth period in Beijing, the optimal water regulation treatment was 100% of design irrigation quota before the end of fruit growth stage, 85% at the postharvest stage and 70% during the end of the growth period.