Hydraulic and Physiochemical Properties of a Hillslope Soil Assemblage in the Ozark Highlands

Abstract

Heterogeneity of infiltration and subsurface redistribution of soil water can have a profound influence on plant growth and productivity as well as water quality. However, substantial uncertainty exists in assessing hydrologic impacts over multiple scales confounded by multiple adjacent land uses. Spatial variabilities of soil surface hydraulic properties are key elements in understanding vadose zone hydrodynamics. The objective of this investigation was to evaluate the effects of land use, soil series, and microtopographic position on soil surface physiochemical and hydraulic properties (i.e., ponded and tension infiltration) during the transition from fall to winter seasons during a period of shallow aquifer recharge. Measurements were made across three Fragiudults (Captina, Nixa, and Johnsburg soil series) on a young alley-cropped agroforestry tract and an adjacent cattle-grazed pasture that constitute a headwater hillslope soil assemblage in the Ozark Highlands. Ponded and tension infiltration rates were affected (P < 0.05) by soils, microtopographic positions, and/or land uses. Tension infiltration rates, averaged across soils and land uses at a pressure head of -3 cm, were nearly twofold greater at the microtopographic low position (17.8 mm h−1) than the high (9.2 mm h−1) position, where the microtopographic high position in the landscape was generally a shallower soil than that at the microtopographic low position. However, when all infiltration measurements were evaluated together, no significant differences in infiltration dynamics were observed among soils, microtopographic positions, or land uses. Thus, a single infiltration pressure head function effectively characterized the hillslope soil assemblage evaluated in this study when shallow aquifer recharge was occurring. Greater bioporosity in upland grazed pastures may serve to naturally decrease hydraulic property variability across soils, which may simplify, rather than complicate, hydrologic partitioning between infiltration and runoff in grassland-based agroecosystems receiving frequent applications of animal manures in the Ozark Highlands.