The Role of Soil Erosion in Regulating Soil C, N, and C/N Ratio Along a Cultivated Black Soil Slope

Abstract

Soil erosion is a crucial process leading to lateral redistributions of surface soil organic carbon (SOC) and total nitrogen (TN). However, its role in the profile distributions of SOC, TN, and their stoichiometry remains unclear. The objective was to evaluate the impact of soil erosion on both the horizontal and vertical distributions of SOC, TN, and the C/N ratio along a cultivated hillslope. On a typical slope farmland in the black soil region of northeast China, the mean annual soil erosion rate (ER) and the profile distributions of SOC, TN, and the C/N ratio were investigated at different slope positions. Both SOC and TN decreased exponentially with depth at each position, except the foots experiencing limited SOC decomposition due to elevated soil moisture and prone to being covered with sediment eroded upslope. The surface SOC and TN at the foots, as a consequence, could be similar to or even lower than those underneath and at the other positions. Given such complexity, no significant correlation was manifested between ER and either surface content (p > 0.05). Nevertheless, the depletion rates of both SOC and TN significantly positively interacted with ER (p < 0.05), as soil erosion tended to enhance the contrasts of soil nutrients thus biomass between the surface and subsurface soils. The C/N ratios of the plough layer were relatively consistent among the slope positions, and no statistical interaction was detected between the mean ratio and ER (p > 0.05). As soil depth increased, however, the C/N ratio changed remarkably at most positions, on account of the presence of the plow pan and/or the deposition of sediments over the original soils.