Exploring optimal measures to reduce soil erosion and nutrient losses in southern China

Heavy rainfall becomes more variable and erratic in the subtropical areas, increasing unpredictable risks of soil erosion and nutrient losses on the sloping farmland. Soil management practice also plays an important role in soil erosion. However, the effects of management practices on soil erosion and nutrient losses in response to heavy rainfall remain uncertain. A field study was carried out under natural rainfalls, including five treatments: bare land as control (CK), downslope tillage (DT), hedgerows with downslope tillage (DT + HG), contour ridge tillage (CT) and straw mulch (SM). The effects of management measures on runoff depth, sediment yield and nutrient losses were evaluated during peanut growth. The results indicated that heavy rainfalls caused severer soil erosion and nutrient losses. Significantly reduced runoff and sediment loss were found in all the conservation measures (p < 0.05). Compared with CK, the runoff depths under DT, DT + HG, CT and SM were reduced by 10%, 37%, 49% and 81% respectively under heavy rainfalls. In addition, sediment loss under DT, DT+HG, CT and SM were 30.81, 7.42, 1.83 and 1.34 Mg ha−1, respectively. These values were 42%, 86%, 97% and 97% lower than that for CK, respectively. TN and TP losses were mainly controlled by sediment yield. The majority of nutrient losses occurred in the particulate fraction (93% of TN and 99% of TP). Generally, much of the TN and TP were transported by the particles <0.05 mm. Over 51% of TN was transported by fractions of <0.05 mm in CK and DT sediments under heavy rainfalls; in CT and SM, this percentage increased to 61% and 74%, respectively. The findings indicated that straw mulch is the most cost-effective management measure to control soil and nutrient losses in sloping farmland of southern China.