Leaching loss of nutrients in tobacco-planting soil under
different biochar adding levels

【Objectives】Leaching loss of soil nitrogen and potassium is generally serious in tobacco cropping regions of Southern China, which leads to fertilizer waste and potential environmental pollution, and greatly limits sustainable production of tobacco. Biochar is porous and stable, and has large surface area. The addition of biochar to soil may increase the adsorption of nutrients and elongate the fertilizer effects. In this study, the leaching loss of main soil nutrients were investigated under different biochar addition levels.【Methods】 Tobacco-planting soil was used in a soil column incubation experiment. Five treatments were designed: no fertilizer (CK); only N, P, K fertilizers (NPK); NPK+ 10% biochar of the soil amount (10%B); NPK+20% biochar (20% B) and NPK+40% biochar (40%B). Each treatment was replicated four times, and the NO-3-N, soluble P and soluble K contents in the leaching water were measured after different days of biochar addition.【Results】 As normal, the leaching amounts of NO-3-N, P and K are increased firstly and then decreased during the incubation In the 21st day of incubation, the leaching amount of NO-3-N and P in NPK treatment was significantly lower than those in the treatments with biochar. Compared to the NPK treatment, the total leaching of NO-3-N in 10%B, 20%B and 40%B treatments were significantly decreased by 13%, 18% and 25%; the total leaching of P decreased by 46%, 61% and 73%, respectively, the total leaching of K in 10%B and 20%B treatments were slightly higher, but not statistically significant. The leaching of K in 40%B treatment was significantly higher than those in the other two biochar added treatments, and was 47% higher than the NPK treatment. At the end of the incubation, the soil pH increased with increasing biochar addition rates. Therefore, it was supposed that the decrease in NO-3-N leaching was mainly attributed to adsorption of biochar. Besides adsorption functions of biochar, the decrease in P leaching maybe due its decreased mobility caused by the increased soil pH, and the increase in K leaching could be the increase in total K input with biochar addition.【Conclusions】 Biochar addition could effectively reduce the leaching losses of NO-3-N and P in soil, but not reduce that of K. Further researches are needed for the proper addition levels of biochar in the comprehensive consideration of nutrient leaching and efficiency.