The benefic effect induced by biochar on soil erosion and nutrient loss of slopping land under natural rainfall conditions in central China

The effects of biochar on runoff and loss of soil and nutrients in the subtropical regions of China are rarely documented. Two field experiments, an orchard and a cropland field were set up, involving two treatments: biochar (BC) and no-biochar (NBC). The effects of BC on runoff volumes and ratios, sediment yield and the level of nutrient losses were monitored and evaluated over three years (2014-2016). Results showed that the treatment of BC induced a significant reduction in the runoff and nutrients losses. By plotting the data collected for the BC application, we observed that the average annual runoff decreased by 19-28%, whereas the average annual sediment yield by 11%. The cumulative values of total nitrogen (N) and phosphorus (P) losses were also substantially minimized by the BC treatment compared with the NBC one (P < 0.05). However, the average annual concentrations of total N and P losses as obtained from the BC plots (16.21 mg L−1 and 0.72-0.99 mg L−1) were still high, and exceeding the wastewater discharge standard (N: 15 mg L−1 and P: 0.5 mg L−1). In addition, under tillage conditions, the BC application led to larger sediments yield (6.5 g m−2) in contrast with the NBC treatment (5.5 g m−2). In general, these findings can suggest that BC exhibits a vital efficiency in the control of soil erosion process, but there is a risk of increasing sediment loss under tillage conditions, which might need to be made up by combined with biological and agronomic managements such as straw mulching or adding polyacrylamide into soil in order to control further soil erosion.