Effect of Sugarcane-Bagasse Biochar On Retention of Ammonium and Nitrate in Soils Cropped With Komatsuna (Brassica rapa).

There has been an increasing trend towards more efficient utilization of sugarcane bagasse (SB). One of the efficient utilizations of SB is to use as adsorbent in carbonized form (biochar) produced from pyrolysis of biomass. Nitrogen (N) leaching from the agricultural soil is the main N loss pathway in forms of ammonium and nitrate. The amount of ammonium and nitrate adsorbed by biochar depends on physicochemical properties of feedstock and carbonization temperature. Therefore, in this study, adsorption and leaching behaviors of ammonium and nitrate in soils amended with sugarcane bagasse biochar (SBB) were investigated. SSBs used in this study were pyrolysed at 400°C (SBB400) and 800°C (SBB800). The adsorption isotherms were developed on respective SSB only or a mixture of each SSB and soil. A column leaching study was performed when respective SSB was applied at 2.5% (w/w) to soil and Komatsuna (Brassica rapa) was planted in the column for 30 days. The adsorption kinetics and adsorption isotherms of ammonium and nitrate on the SSB only and SSB/soil mixture followed well the pseudo-second order kinetic equation and the Langmuir equation, respectively. The amount of ammonium adsorbed by the SBB/soil mixture was greater than that by the soil only due to cation adsorption capacity of SSB on acidic surface functional groups. In the leaching study, ammonium leaching from chemically fertilized column was greater than those from both SBB400 and SBB800 columns, regardless of the presence of the plant. Nitrate leaching was reduced in the SBB800 column compared with that in the chemically fertilized column. Therefore, SBB800 application to soil may increase retention hence reduce leaching of ammonium and nitrate.