Effects of Sugarcane Bagasse Biochar on Ammonium and Nitrate Adsorption and Leaching in a Japanese Tropical Soil Cropped with Japanese Mustard Spinach (Brassica rapa)

This study investigated the dynamics of ammonium-nitrogen (NH4+-N) and nitrate-nitrogen (NO3–-N) adsorption and leaching in a Japanese tropical soil amended with sugarcane bagasse biochars (SBBs) in the presence of plant. Adsorption and column leaching studies were conducted in a laboratory in Japan, and the column study was performed for 21 days. Biochar was produced from sugarcane bagasse at the maximum pyrolysis temperatures of 400°C (SBB400) and 800°C (SBB800) for use in the experiments. Adsorption isotherms for NH4+-N and NO3–-N were developed for soil only, SBB400-amended soil, and SBB800-amended soil. Column leaching study included 6 treatments: fertilizer only, fertilizer and plant, fertilizer and SBB400, fertilizer and SBB400 and plant, fertilizer and SBB800, fertilizer and SBB800 and plant. This study showed that soil and SBBs-amended soils fitted well into the Langmuir adsorption model for NH4+-N and NO3–-N (r2= 0.983–0.994 and 0.956–0.970, respectively). Application of SBBs to soil significantly decreased cumulative NH4+-N leached from the soil (P < 0.05) because of increased adsorption capacity due to high acid functional groups and increased soil water holding capacity (WHC) due to high specific surface areas and pore volumes, regardless of the presence of plant. However, the SBBs application did not affect the adsorption capacity for NO3–-N because of negatively charged surfaces. However, cumulative NO3–-N leached was significantly reduced (P< 0.05) due to increased soil WHC, regardless of the presence of plant. Therefore, more soil water contents retained and less NO3–-N leached from the soil may have contributed to greater plant growth with the SBBs application. This study showed that the SBBs application to soil could enhance adsorption capacity for NH4+-N but not for NO3–-N, nevertheless increase soil WHC and reduce leaching of both NH4+-N and NO3–-N, thus contributed to increased plant growth.