Regional variations in plant-available soil water storage and related driving factors in the middle reaches of the Yellow River Basin, China

Available soil water is considered the most important water resource for food production in agricultural ecosystems and sustainable vegetation restoration in arid and semi-arid regions. Compared to soil water content, plant-available soil water storage (ASWS) directly indicates the amount of soil water that can be used by plants. Understanding the spatial characteristics and controlling factors of ASWS can aid in improving the ability of the agricultural ecosystem to resist extreme natural disasters and stabilise grain production in China. In this study, ASWS in the 0–5.0 m profile was measured in an area of approximately 36.9 × 10⁴ km² in the middle reaches of the Yellow River Basin. The total ASWS in the 0–5.0 m profile of the study area was 113 × 10¹⁰ m³, 85% of which was stored in the > 450 mm rainfall zones. The spatial variation in ASWS was mainly controlled by climate and edaphic properties of the 0–1.0 m soil layer and < 450 mm rainfall zone. Regarding the 1.0–5.0 m soil layer and > 450 mm rainfall zone, edaphic properties were the dominant factors determining the spatial characteristics of ASWS. Based on the spatial characteristics of ASWS, the shallow soil water (0–1.0 m) in the middle region and deep soil moisture (1.0–5.0 m) in the southern region of the study area can support the rational use of soil water in agricultural and vegetation restoration activities. Large-scale revegetation activities using trees or shrubs might not be the optimal choice in regions with mean annual precipitation < 450 mm. Knowledge of the spatial characteristics and contributions of the ASWS controlling factors is indispensable for reasonable agricultural regionalisation and vegetation restoration, as well as for an invulnerable and stable grain output system.