Assessment of irrigation efficiency for arid-zone spring wheat production under flood irrigation

Understanding the availability of irrigation water at various growth stages is crucial for guiding agricultural scheduling in arid areas with limited water sources. However, challenges persist in swiftly and synchronously tracking water utilization post-irrigation, especially in discriminating between evaporation and transpiration. By utilizing high-frequency water vapor and carbon dioxide flux data collected by the eddy-covariance system, we employed the evapotranspiration partitioning method based on flux-variance similarity (FVS) to continuously monitor evaporation and transpiration. Through evaluating the effectiveness of the FVS-based partitioning approach with in-situ micro-lysimeters measurements and analyzing the impact of environmental factors using principal component analysis, the partitioning results, incorporating soil moisture content and groundwater levels, were utilized to assess the availability of irrigated water in a wheat field. The findings demonstrated that the refined partitioning method successfully separated evapotranspiration into transpiration and evaporation. Transpiration, contributing to 54.8%, was the primary driver of evapotranspiration (454 mm) during the growth period, while evaporation (205 mm) played a significant role during the seeding and maturation stages. Overall, evapotranspiration consumed 75.5% of the irrigated water (605 mm), with the remaining 24.5% recharged to the groundwater throughout the wheat growth period. These results indicated that 58.4% (comprising evaporation and deep leakage, totaling 353 mm) of irrigation water was not absorbed by the crops. Environmental factors such as air temperature, relative humidity, vapor pressure deficit, and net radiation subtly and consistently influenced the ratio of evaporation and transpiration, with changes in the plant canopy having the most substantial impact on water-use efficiency. Notably, the effects of irrigation events on water vapor fluxes were significant but temporary.