Spatial variation of soil water content in topsoil and subsoil of a Typic Ustifluvent

Water content is a fundamental property affecting plant growth, transport and transformation of soil nutrients, and water and energy budgets in the soil–plant system. Its spatial variation has important implications for all these processes. In this study, spatial variation in soil water contents was evaluated at pressures of −0.033 (θ−0.033 MPa), −0.10 (θ−0.10 MPa), and −1.50 MPa (θ−1.50 MPa) at the soil depth from surface to the lower and of a plow layer in a Typic Ustifluvent in an 8.5 ha level area (1–2% slope). Topsoil (0.0–0.30 m) and subsoil (0.31–0.60 m) were sampled based on a regular grid spacing of 25 m-by-25 m. Variables θ−0.033 MPa, θ−0.10 MPa, and θ−1.50 MPa were measured with a pressure plate apparatus. Results were evaluated and compared with conventional statistics and geostatistics. Coefficient of variation (CV) for soil water content increased as soil water pressure decreased in both topsoil and subsoil. Semivariance analysis and ordinary block kriging-produced surface maps for θ−0.033 MPa, θ−0.10 MPa, and θ−1.50 MPa showed that topsoil and subsoil were similar in spatial variation of water content at all three corresponding soil water pressures. The geostatistical range values were between 298 m (θ−0.10 MPa in topsoil) and 486 m (θ−0.10 MPa in subsoil), both indicating a strong spatial dependence of soil water content. The semivariograms for θ−0.033 MPa, θ−0.10 MPa, and θ−1.50 MPa were similar in shape in both topsoil and subsoil. Cross-dependence between sand content and soil water contents showed that soil texture controlled the spatial variation of water contents at the site, at all depths and pressures evaluated.