Slope aspect affects soil quality and its response to soil erosion on temperate gently sloping farmlands

Slope aspect is a significant terrain attribute influencing soil physical and chemical processes. Yet its impact on soil quality and erosion has rarely been studied on gently sloping farmlands. The objective was to evaluate the effects of slope aspect on soil quality and its response to soil erosion in the black soil region of northeast China, a temperate environment featuring gently sloping farmlands. Over a nearly north-south symmetric sloping farmland spanning ∼3500 m, fifteen soil physical and chemical properties were investigated at every 40 m, and an integrated soil quality index (SQI) was calculated combining principal component analysis and scoring functions. The mean annual erosion rate (ER) was estimated using the cesium-137 tracing technique. Compared to the south-facing slope, the north-facing slope possessed significantly lower pH and higher saturated hydraulic conductivity, sand content, and almost all the essential nutrient contents, therefore overall better soil quality (p < 0.05). No statistical difference was spotted in ER between the two slopes (p > 0.05); however, erosion was found to deteriorate soil quality via distinct pathways. On the north-facing slope, erosion affected SQI predominantly through its negative impact on soil organic carbon content and wet-aggregate stability, and conservation tillage practices were suggested. However, on the south-facing slope, the detrimental influence was primarily driven through the depletion of soil nutrient contents, particularly available phosphorus and total nitrogen, and contour tillage and hedgerows were strongly recommended. These findings hold important practical implications for agricultural management in temperate environments.