Spatial Variability of Water Fluxes in Soil: A Field Study

Abstract

AbstractKnowledge of spatial variability of soil properties is important for soil sampling and modeling water and solute transport through soil. A field study was conducted on a Silawa‐variant loamy fine sand (fine, mixed, thermic Udic Paleustalf) in Brazos County, Texas, to evaluate spatial variability and convergence and divergence of water fluxes through the soil profile. A 7 by 14 grid of interception cells (each 25 by 25 mm) was built to collect surface‐applied water at 0.3‐, 0.9‐, and 1.2‐m depth. The interception cells were installed on the ceilings of tunnels that had been hand dug horizontally into the walls of a large backhoe‐dug pit. Water was applied under a positive head of ≈50 mm in a 1.2 by 1.2 m infiltration square. Normal and lognormal probability functions were fitted to frequency distributions of intercepted fluxes from topsoil and subsoil, respectively, with correlation coefficients of 0.95 and higher. Most nonmatrix flow was found at 0.9 m in the Bt2 horizon. We speculate that fluxes were most heterogeneous in this horizon because of associated soil texture and structure. Compared with soil at 0.3 and 1.2 m, texture was finer, peds were larger, and clay films were more abundant at 0.9 m. This relationship with pedologic development suggests that descriptions of texture and structure might be used to predict spatial distributions of fluxes and design sampling schemes. Convergence of water flowpaths was observed from 0.3 to 0.9 m while divergence occurred from 0.9 to 1.2 m.