Variations in soil quality indicators under different cultivation ages and slope positions of arable land in the Mollisol region of China

Arable land use change and ages from natural forests alter soil quality, i.e., organic carbon and nutrient losses. Landscape fosters a more complicated spatial distribution of soil quality indicators by soil erosion, resulting in deposition at the lower slope. Although the soil quality index (SQI) has been widely used to assess soil quality, studies comparing the effects of cultivation ages and slope positions on soil quality evolution are rare. Here we report variations in soil quality and corresponding indicators under different cultivation ages (15-yr, 20-yr, and 30-yr) and sloping positions (upper-, middle-, and lower-slope) in the Mollisol region of China. We found a decreasing trend occurred for the soil organic carbon (SOC) and total nitrogen (TN) with cultivation ages. Simultaneously, from upper slope to lower slope position, an increasing trend occurred for the soil fertility properties (i.e., SOC, TN, available potassium-AK, total phosphorus-TP, and available phosphorus-AP), and a decreasing trend occurred for total potassium (TK) and pH. We found that TN, pH and sand content were the most representative indicators for the minimum data set, which represents soil quality under diverse cultivation ages. Moreover, the SQI decreased with increasing cultivation ages while increasing from the upper- to the lower slope. Notably, SQI was primarily affected by the cultivation ages (14.6%) with no considering lower slope positions. While the slope position was the main contribution to SQI (21.6%) with considering lower slope position. We highlight that although the minimum data set was the most feasible approach for assessing soil quality under different ages of cultivation in the Mollisol region. For diverse slope positions and elevations, variations in key soil quality indicators and their interactions are necessary to be re-considered and assessed due to the soil erosion and deposition processes.