Optimizing Biochar Concentration for Mitigating Nutrient Losses in Runoff: An Investigation into Soil Quality Improvement and Non-Point Source Pollution Reduction

Rainfall runoff can lead to a reduced soil quality and non-point source pollution through the removal of nutrients from the topsoil that are not utilized by plants. The use of biochar is an effective method to solve this problem. The aim of this study was to determine the optimal concentration of added biochar to reduce the soil particle, NH4+ -N (AN), NO3− -N (NN), and total phosphorus (TP) losses. Additionally, the inhibitory mechanisms of biochar that mitigate nutrient loss were revealed using FT-IR (Fourier-transform infrared) spectrometry and SEM (scanning electron microscopy). Compared with the control group, the addition of 2% biochar resulted in decreases in the AN, NN, TP, and soil erosion rates of 57.08%, 4.25%, 30.37%, and 22.78%, respectively; the leaching loss rates of AN and NN were reduced by 6.4% and 9.87%, respectively. However, it should be noted that the use of biochar resulted in an increase in the loss of soil particles smaller than 20 μm, while it resulted in a decrease in the loss of soil particles larger than 20 μm. Adsorption processes on the benzene ring may have caused the absorption peak at approximately 1600 cm−1 to disappear after adsorption. The porous structure of biochar and the presence of hydrophilic groups (such as hydroxyl groups) facilitate adsorption reactions. The optimal concentration of added biochar was 2%.