Infl uence 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. Th e objective of this study was to evaluate the eff ects of bagasse charcoal (sugarcane [Saccharum offi cinarum L.] bagasse-derived biochar) on nitrate (NO₃^-) leaching from Shimajiri Maji soil, which has low waterand fertilizer-retaining capacity. Th e nitrate adsorption properties of bagasse charcoal formed at fi ve pyrolysis temperatures (400-800^oC) were investigated to select the most suitable bagasse charcoal for NO₃^- adsorption. Nitrate was able to adsorb onto the bagasse charcoal formed at pyrolysis temperatures of 700 to 800^oC. Nitrate adsorption by bagasse charcoal (formed at 800^oC) 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^-1 KNO₃ solution. Measurements suggested that the saturated and unsaturated hydraulic conductivity of bagasse charcoal (800^oC)-amended soils are aff ected 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 NO₃^- leaching studies using bagasse charcoal (800^oC)-amended soils with diff erent charcoal contents (0-10% [w/w]), the maximum concentration of NO₃^- in effl uents from bagasse charcoal-amended soil columns was approximately 5% less than that from a nonamended soil column because of NO₃^- adsorption by bagasse charcoal (800^oC). We conclude that application of bagasse charcoal (800^oC) to the soil will increase the residence time of NO₃^- in the root zone of crops and provide greater opportunity for crops to absorb NO₃^-.