Impacts of different management measures on soil nutrients and stoichiometric characteristics for sloping farmland under erosive environments in the Three Gorges Reservoir Area, China

Soil erosion exacerbates the loss of soil nutrients and directly affects the soil stoichiometric characteristics. However, the impacts of different erosion conditions and farmland management measures on soil nutrients and their stoichiometry remain unclear. Herein, field observations were conducted in purple-soil sloping farmland in the Three Gorges Reservoir Area, China, using the artificial shovel soil test method. The soil nutrient contents and stoichiometric characteristics of the topsoil under three management measures (no fertilization, CK; chemical fertilizer, F; biochar+chemical fertilizer, BF) and five erosion conditions (erosion thicknesses of 0, 5, 10, 15, and 20 cm) were analyzed. The SOC, TN, TP, TK, AN, AP, and AK contents of the three management measures followed overall decreasing trends with increasing erosion thickness. Under the same erosion condition, the content of nutrient elements in the three treatments followed the trends of BF > F > CK, and the soil nutrient content of the BF treatment was significantly higher than that of the CK treatment (P <0.05). With the increasing erosion thickness, soil C/N, C/P, and N/P ratios of the three treatments showed decreasing trends. The average soil C/N, C/P and N/P ratios for the three treatments were 10.55, 16.92, and 2.09, respectively, i.e., lower than the global and national averages. A lower C/N ratio indicats a faster SOM mineralization rate in the region, with the SOM cumulative rate lower than the decomposition rate. Lower C/P and N/P ratios indicated that crop growth was limited by N, resulting in a state of N deficiency and P enrichment in the soil nutrient in this region, thereby limiting soil productivity. Based on multi-attribute decision making, soil nutrient recovery index, and the characteristics of the response surface, the application of biochar+chemical fertilizer is conducive to alleviating the supply-demand contradiction between crops and soil nutrients, representing an effective way of improving soil fertility. However, further research is required to determine when the application of biochar leads to SOM accumulation that exceeds decomposition. These results provide a scientific basis for the restoration and reconstruction of soil ecosystems in sloping farmlands.