Root distribution and water competition mechanism between farmland shelterbelts and cotton under drip irrigation in an oasis of Xinjiang, China 后印本

摘要: Farmland shelterbelts play a crucial role in protecting arable land in arid and semi-arid areas, but they may also compete for soil water with crops in agroforestry systems. Film-mulched drip irrigation in adjacent farmland substantially alters the water supply dynamics of shelterbelts, yet studies on the hydrological interactions between farmland shelterbelts and crops under this irrigation regime in the arid oasis areas along the desert margins of Xinjiang Uygur Autonomous Region, China remain limited. This study conducted an experiment in an oasis at the southern margin of the Gurbantunggut Desert in Xinjiang over the 2022–2024 growing seasons. We characterized the evapotranspiration (ET) patterns of the cotton field and adjacent Populus shelterbelt, quantitatively evaluated their interspecific water relationships, and examined fine root distribution to identify the zones and intensity of water competition. The results indicated that during the seedling and flowering–bolling stages, cotton field ET exceeded shelterbelt ET by 56.0%–66.1%; however, during the boll-opening stage, shelterbelt ET was 24.2% higher than cotton field ET. Within the 0.1H–0.5H into the cotton field from the shelterbelt–cotton field interface (where H is the tree height), Populus exhibited a competitive advantage in the 20–40 cm soil layer, with a competitiveness index of 0.083–0.146 (versus 0.039–0.051 for cotton), while competition was weak in the 40–60 cm layer. At 0.1H, Populus root biomass density (RBD) and root length density (RLD) were 1.0–15.2 and 6.0–50.0 times those of cotton, respectively; at 1.0H, cotton RBD accounted for 63.0%–93.5% of total root biomass; and no Populus roots or evidence of water competition were detected at 2.0H and 3.0H. Supplemental irrigation should be applied to cotton fields adjacent to shelterbelts to offset water loss from interspecific competition, particularly during the boll-opening stage. The findings provide a practical basis for optimizing agricultural water management in oasis–desert agroforestry systems under film-mulched drip irrigation and offer regional empirical evidence for global research on water competition in arid-zone agroforestry systems.