Soil water content variations and hydrological relations of the cropland-treebelt-desert land use pattern in an oasis-desert ecotone of the Heihe River Basin, China

• The soil water content variation and hydrological relation in the cropland-treebelt-desert system was investigated.
• The cropland had great soil water content in upper layer but noticeably small value in lower layer.
• The decline process of soil water content pulse could be described by an exponential function.
• The soil water uptake by treebelt root from cropland decreased logarithmically with distance.
• The percolation from cropland irrigation was an important water source for treebelt and desert plants.

This study considered the cropland-treebelt-desert system in the arid inland river basin as an entire continuum to investigate the soil water content variation and hydrological relation. For this objective, the volumetric soil water content and plant root distribution was measured to 300 cm depth along a cropland-treebelt-desert site at the oasis-desert ecotone in the Heihe River Basin, China. The results showed that the mean soil water content in the 0–200 cm layer was greater in the cropland (8.88%) than that in the treebelt (5.78%) and desert (4.37%) as a result of frequent irrigation events. However, the cropland had noticeably lower mean soil water content below 200 cm depth (14.27%), compared to treebelt (18.07%) and desert (17.30%) with deeper roots to suck up groundwater. The decline process in soil water content pulse of the cropland and treebelt after irrigation event could be well described by an exponential decay function, and the soil water loss rate was greater in the cropland (0.45–0.70%/day) than that in the treebelt (0.32–0.47%/day). The hydrological relation between treebelt and cropland in the upper soil layer was mainly occurred by treebelt root water uptake from cropland. The biomass of fine treebelt root extended into the cropland decreased logarithmically with the distance from the cropland-treebelt interface, which resulted in the smaller soil water content in the cropland with more proximity to the treebelt. The hydrological relation in the lower soil layer among cropland-treebelt-desert was caused by groundwater recharge, as cropland irrigation raised up the groundwater level to replenish the deep soil layer. The results indicated that the percolation in the cropland was an important water source for the growth of treebelt and desert plants. This study could provide scientific basis for land use pattern design and water resources management in the arid inland river basin.