Infiltration properties affected by slope position on cropped hillslopes

Soil infiltration properties (SIPs) and their spatial variability are essential for simulating hydrologic and erosion processes. Intensive water erosion likely leads to large spatial heterogeneity of soil particle distribution, thus the large spatial variability of general soil properties, such as SIPs. Nevertheless, little is known about the spatial variabilities of SIPs along long, gentle hillslopes and their dominant controlling factors. This study was conducted to investigate SIPs under different slope positions under agricultural management and to identify dominant SIP -related factors in the Black-soil region of Northeast China. Soil infiltration properties were determined at five slope positions (i.e. upper, middle-upper, middle, middle-lower, and lower) on two approximate 5 % hillslopes using a disc infiltrometer under three pressure heads (-3,-1.5, and 0 cm). Results showed that the initial infiltration rate (IIR), steady infiltration rate (SIR), and saturated hydraulic conductivity (KS) varied from 0.11 to 0.47 mm min -1, 0.04 to 0.30 mm min -1, and 0.04 to 0.29 mm min -1, respectively. Soil infiltration properties generally increased initially, then decreased from the upper to the lower position along the hillslope. The middle -slope position had the numeric maximum SIPs, and SIPs were significantly greater than those of the upper and lower slope positions. Compared to the middle-slope position, IIR, SIR, and Ks of the upper and lower slope positions were lower by 50.9, 61.1, 63.6 and 33.8, 32.3, 34.6 %, respectively. Initial infiltration rate, SIR, and Ks were positively correlated with sand content (r = 0.60, 0.69, 0.69; p < 0.01), total porosity (r = 0.67, 0.71, 0.71, respectively; p < 0.01), saturated soil water content (r = 0.62, 0.70, 0.71, respectively; p < 0.01), and gravel content (r = 0.48, 0.66, 0.70, respectively; p < 0.01), but were negatively correlated with silt (r =-0.50,-0.49,-0.49, respectively; p < 0.01) and clay (r =-0.50,-0.64,-0.63, respectively; p < 0.01) contents, bulk density (r =-0.67,-0.70,-0.70, respectively; p < 0.01), and physical crust thickness (r =-0.63,-0.73,-0.73, respectively; p < 0.01) across positions of the two hillslopes. The result of redundancy analysis indicated that physical crust thickness, bulk density, and water-stable aggregate and clay contents were the dominant factors attributed to the variation in SIPs under different slope positions, and collectively they explained 74.6 % of the total variation of SIPs. Physical crust thickness alone explained the largest proportion (49.9 %) of the variation of SIPs. Results will be helpful for improving precision of hydrologic and erosion processes modeling and sus-tainable soil management on long, gentle hillslopes in the agricultural region of Northeast China.

Automated summary

This study investigated the soil infiltration properties (SIPs) at different slope positions in the Black-soil region of Northeast China and identified the dominant factors controlling these properties. The results showed that SIPs varied along the hillslope, with lower permeability at the upper and lower slope positions and higher permeability at the middle slope position. The infiltration properties were significantly correlated with soil composition and physical characteristics.