Land Use Effects on Soil Hydraulic Properties

Tillage alters the pore structure and hydraulic properties of soils. Likewise, reestablishment of grass on cropland will, over time, produce changes in soil hydraulic properties that can influence the amount of plant available water. We conducted a study to characterize and compare soil hydraulic properties on adjacent native grassland, cropland, and Conservation Reserve Program (CRP) sites at three locations in the Texas High Plains. A tension infiltrometer was used to measure unconfined, unsaturated infiltration over a range of water tensions (0.05, 0.5, 1.0, and 1.5 kPa) at the soil surface. Intact soil cores were sampled within the Ap and Bt horizons to determine bulk density and water desorption curves, (h). Unsaturated hydraulic conductivity over the range of tensions K(h) was estimated using Wooding’s equation for steady state flow from a disk source. The van Genuchten-Mualem model was simultaneously fitted to K(h) and (h) data to obtain parameter values for each land use treatment. Mean near-saturated hydraulic conductivities of cropland were not significantly different from grassland. However, at 1.5 kPa supply tension, cropped soils had a mean unsaturated conductivity four times greater than grassland. CRP sites had the lowest (P < 0.05) near-saturated hydraulic conductivities, which suggests that, after 10 years, grasses had not fully ameliorated changes in pore structure caused by tillage. Results of a 10-day simulation of evaporation from a bare soil suggest that the larger unsaturated conductivities measured for sweep-tilled cropland leads to increased evaporative losses of water as compared with other land uses. R.C. Schwartz et al. / ISTRO- 2000