Influence of sugarcane bagasse-derived biochar application on nitrate leaching in calcaric dark red soil

Application of biochar has been suggested to improve water- and fertilizer-retaining capacity of agricultural soil. The objective of this study was to evaluate the effects of bagasse charcoal (sugarcane [ L.] bagasse-derived biochar) on nitrate (NO) leaching from Shimajiri Maji soil, which has low water- and fertilizer-retaining capacity. The nitrate adsorption properties of bagasse charcoal formed at five pyrolysis temperatures (400-800° C) were investigated to select the most suitable bagasse charcoal for NO adsorption. Nitrate was able to adsorb onto the bagasse charcoal formed at pyrolysis temperatures of 700 to 800° C. Nitrate adsorption by bagasse charcoal (formed at 800° C) that passed through a 2-mm sieve was in a state of nonequilibrium even at 20 h after the addition of 20 mg N L KNO solution. Measurements suggested that the saturated and unsaturated hydraulic conductivity of bagasse charcoal (800° C)-amended soils are affected by changes in soil tortuosity and porosity and the presence of meso- and micropores in the bagasse charcoal, which did not contribute to soil water transfer. In NO leaching studies using bagasse charcoal (800° C)-amended soils with different charcoal contents (0-10% [w/w]), the maximum concentration of NO in effluents from bagasse charcoal-amended soil columns was approximately 5% less than that from a nonamended soil column because of NO adsorption by bagasse charcoal (800° C). We conclude that application of bagasse charcoal (800°C) to the soil will increase the residence time of NO in the root zone of crops and provide greater opportunity for crops to absorb NO.