Spatial Distributions of Soil Surface-Layer Saturated Hydraulic Conductivity and Controlling Factors on Dam Farmlands

Saturated hydraulic conductivity (Ks) is a critical soil property affecting water flow and solute transport. In the Loess Plateau of China, sloping farmlands have been increasingly replaced by dam farmlands to achieve higher crop yields and more importantly to control soil erosions. It is necessary to understand the spatial pattern of near-surface K (S) on those newly formed dam farmlands, because the land surface processes (e.g., erosion that is controlled by overland flow) are largely determined by the spatial distribution of near-surface Ks. In this study, near-surface Ks (e.g., 5 cm depth of the surface layers) was measured using 336 undisturbed soil samples collected from two dam farmlands located in the Liudaogou catchment, a heavily studied catchment in the Loess Plateau of China. Based on classical and geostatistical analyses, the soil properties at the filled dam farmland showed more spatial variations compared to the silting dam farmland. Statistical scale-invariance was evaluated using the Hurst scaling parameter (H) for different soil parameters. The H values ranged from 0.646 to 0.877, indicating certain degrees of statistical scale-invariance and long-range dependency within the spatial range. The bulk density (D-b), saturated water content (SW), sand content (SA), silt content (SI), and clay content (CL) were shown to affect the K (S) values significantly with SW, SI, and CL negatively and SA and D-b positively correlated with K (S) . The highest K (S) value was found at the middle portion of the dam farmlands and the lowest value was found at the locations with the minimum occurrence of surface runoff. In addition, the areas with lowest K (S) values corresponded to the areas with the highest CL, SI, and SW. The results showed that disturbing soil structure by planting crops would benefit the floodwater control on dam farmlands due to increased Ks and the flooding on dam farmlands would be eased due to the silting process.