RESUMO
Planted forests in semi-arid regions provide invaluable ecological functions such as windbreak, sand fixation, carbon fixation, and oxygen release, improving the ecological environment and maximizing the carbon sink benefits of forests. Therefore, accurately assessing non-productive water losses in water-scarce regions is crucial for estimating water requirements of irrigation-dependent plantations. From March to October 2023, we collected the stable isotopes of precipitation, irrigation water, soil water, and other relevant data. The Craig-Gordon model was used to evaluate the non-productive water losses in irrigated Platycladus orientalis plantations, focusing on the dissipation and vertical migration process under both sufficient and insufficient water supply conditions. The results demonstrated that preferential flow and piston flow coexisted during soil water infiltration, while both types occurred under sufficient watering conditions, but piston flow dominated when there was insufficient watering. We estimated the average non-productive losses for irrigated P. orientalis plantations at 27.0 %, with peak losses up to 40.3 %. Moreover, we observed a lower rate of non-productive losses under sufficient water supply conditions (12.2 %) compared with insufficient water supply conditions (33.6 %). Our results indicated that vertical migration pathway of soil water emerged as a significant determinant factor affecting non-productive water losses, and also influenced by meteorological factors, water inputs, and soil properties. To optimize water utilization in semi-arid irrigated mountainous plantations, we recommend reducing amount of each irrigation and increasing frequency of irrigation.