Infiltration process of irrigation water in oasis farmland and its enlightenment to optimization of irrigation mode: Based on stable isotope data

The transmission of water through soil is one of the critical links to reflect the hydrological process. At present, there are controversies about the infiltration of farmland irrigation water and the replacement of old and new water in arid areas, which significantly reduces the scientific nature of the irrigation policy formulation. In this study, we monitored the temporal and spatial changes of stable isotopes of soil water in Minqin Oasis farmland, analyzed the infiltration process of irrigation water, used the MixSIAR isotope mixture model to estimate the contribution of irrigation water to soil water and evaluated their effective contribution time to different soil layers. This study suggests that: The temporal and spatial changes in pore water isotope reflect the process of artificial irrigation and evaporation. Within 5 days after irrigation, the average contribution rate of irrigation at 0–20 cm, 20–60 cm, and 60–100 cm soil layers was 31.11 ± 17.74%, 19.17 ± 12.72%, and 31.56 ± 12.42%, respectively. Under the influence of soil water content, topography, and plastic film cover, the effective contribution time of irrigation water to 0–20 cm and 60–100 cm soil layers was more than 5 d, and the effective contribution time to the 60–100 cm soil layer is only 4 d. The research results will help understand the hydrological process of farmland in the arid oasis area and provide a scientific basis for improving agricultural irrigation mode, which will help realize the sustainable development of regional agriculture.