Field measurement of saturated hydraulic conductivity at the hillslope scale under different soil series and management practices

Abstract

Heterogeneity of saturated hydraulic conductivity (Ksat) was investigated at the hillslope scale in the South Amana Subwatershed (SAS), IA. Three fields of different soil series, and management practices (tilled, no-till, CRP) were examined at the SAS. Ksat was measured using 30 semi-automated double ring infiltrometer. Soil cores were also collected in the vicinity of the Ksat measurements via a truck-mounted Giddings Probe. Core sample analysis suggests that the spatial variability in Ksat very much reflects the overall soil texture variability found in the tested fields. The spatial variability of Ksat was log-normally distributed, which closely follows the distribution of the surface microroughness. Ksat varied over 3-orders of magnitude within the tested fields. The high sensitivity of Ksat was a good index to identify soil heterogeneity. Comparison between the published soil maps and observed soil series of the collected cores shows that erosion to varying degrees has occurred along the hillslope. Along the sides of the hillslope as we move downhill, the loam layer was found much deeper than along the centerline of the hillslope. This finding was indicative that significant erosion has occurred along the centerline of the hillslope. An outcome of the severe erosion was that the soil texture differed between the centerline and the sides. This different texture was found to affect Ksat at similar slope positions and land cover.