Seasonal variation of deep soil moisture under different land uses on the semi-arid Loess Plateau of China

PurposeDeep soil moisture has been considered to be critical for plant survival in water-limited ecosystems. The limited precipitation on the semi-arid Loess Plateau is the only water source for soil moisture and is unevenly distributed throughout the year. Characterizing the seasonal changes in deep soil moisture in relation to land use types and structures is important for the sustainability of vegetation restoration in this region.Materials and methodsA total of 27 experimental sites along seven transects were selected in the Jiegou catchment on the semi-arid Loess Plateau. These sites were covered by five land use types: native grassland, traditional farmland, abandoned farmland, and 5-year and 7-year Robinia pseudoacacia (RP) forestlands. Soil moisture measurements were conducted during three seasons (spring, summer, and fall) at soil depths of 0 to 5m in 0.2-m increments, and 2025 disturbed soil samples were collected to determine the gravimetric soil moisture content using the oven-dry method (24h at 105 degrees C). The depth-averaged soil moisture was compared among different seasons and land use types using one-way ANOVA and significance tests.Results and discussionAmong the seasons, the depth-averaged soil moisture had the following order: fall > spring > summer. In the shallow layers (above 2m), soil moisture in summer was significantly lower than that in spring and fall (p<0.05). The vertical distribution characteristics of soil moisture (0-5m) were similar among the land use types during each season but different among the seasons for each land use type. In general, the depth-averaged values of soil moisture among the land use types were on the order of native grassland > farmland > forestland. This finding indicated that afforestation drastically decreased deep soil moisture, particularly in summer. Furthermore, the different land use structures significantly influenced the spatial distribution of deep soil moisture during each season.ConclusionsThis study highlights the seasonal changes in both shallow and deep soil moisture under various land use types, which provides insights into the sustainable use of deep soil moisture and rational land use management on the semi-arid Loess Plateau of China.