Optimizing irrigation in arid irrigated farmlands based on soil water movement processes: Knowledge from water isotope data

Abstract

Understanding soil water movement processes in cultivated land is crucial for developing sound irrigation strategies. However, current knowledge regarding the fate of water after irrigation remains incomplete. Therefore, this study was conducted in a maize field in Datan Township, Minqin County, where precipitation, irrigation water, soil, and maize stalk samples were collected during the growing seasons of 2018 and 2019 and subjected to stable hydrogen and oxygen isotope analysis. Soil water infiltration and evaporation losses following irrigation were analyzed using a soil water balance equation and isotope mass conservation. Evapotranspiration partitioning at the hourly scale in Datan Township farmland after irrigation was quantitatively analyzed using the isotope steady-state (ISS) assumption. The results showed that: (1) During the maize growing season after irrigation, an average of approximately 24.65 % of the irrigation water infiltrated below 1 m, and 13.6 % was lost to soil evaporation. (2) Following irrigation, the ratio of transpiration to evapotranspiration (T/ET) at the hourly scale was higher from 7:00 PM to 8:00 AM the next day, indicating lower crop water loss and more efficient water use by vegetation during this period. (3) Variations in irrigation timing caused deviations in hourly T/ET fluctuations. Midday irrigation increased the diurnal range of T/ET, resulting in a lower daily average T/ET value, while morning or evening irrigation increased the daily average T/ET value. This research enhances our understanding of farmland hydrological processes in the arid northwest region. Based on our findings, we propose that reducing single irrigation amounts, adjusting irrigation timing, and adopting subsurface drip irrigation are effective water-saving strategies for arid farmland.