Different supplemental irrigation methods result in discrepant water use efficiency and yield by changing steps of water use process in dryland wheat

Abstract

Supplemental irrigation (SI) at critical growth stages is a practical way to mitigate water shortage of winter wheat in dryland. However, the yield performance after SI is unstable in different precipitation years. To obtain a better understanding about the applicability of SI in dryland, the utilization efficiency of precipitation and irrigation water (IUE) was divided into 5 sequential ratios: water storage ratio, water consumption ratio, water transpired ratio, transpiration efficiency and harvest index. In this study, those ratios were investigated under four SI methods: no irrigation (W₀), SI once at jointing (W_j), SI once at booting (W_b) and SI twice at jointing and booting (W_j+b) throughout four years. Our results showed that water storage ratio was increased under all SI treatments, but water transpired ratio was only significantly increased under W_j and W_j+b, due to their greater development of plant population compared to W₀. Thus, wheat yield was greatly improved by 7–12 % under W_j and W_j+b than that under W₀ in dry and normal years. However, IUE was significantly decreased under W_j+b. Compared with W₀, W_j+b had higher evaporation during the fallow period and lower water consumption ratio. Furthermore, 100–300 cm subsoil water utilization was decreased under W_j+b from jointing to harvest time due to the low root length density (RD_L) in subsoil. Under W_j, evaporation, subsoil water utilization and RD_L were not negatively affected and water use efficiency was increased compared to W₀. Thus, SI once at jointing stage is a more suitable practice in dryland wheat farmland when considering the dual goal of effectively using water while increasing yields under worse precipitation year.