Effect of Biochar Application on Water Quality in Sugarcane and Rice Paddy Fields.

Biochar application in cultivating soils has been suggested as a soil conditioner for improving soil productivity and enhancing soil carbon sequestration. However, effect of biochar on subtropical agricultural production regions is not yet fully understood. In this study, field experiments were carried out in both sugarcane and rice fields investigate the effect of biochar on water quality. Biochars produced from sugarcane and rice harvest residues as well as pinewood were applied at a rate of 8960 kg/ha. Runoff water samples were collected using Avalanche ISCO auto sampler at sugarcane site whereas surface water was periodically collected from the rice site. Various soil physical and chemical properties were also characterized at the beginning, during, and the end of the experiment.  Biochar amendment lightly decreased the electrical conductivity and total organic carbon in standing water of rice fields but the effect on sugarcane fields were variable. Wood biochar-treated soil showed lower total P runoff than the sugarcane biochar–treated soil. In addition, biochar treatment had significant impact on bulk density and moisture conservation of soil. The results also showed that biochar amended soil had lower N₂O and CH₄ but higher CO₂ emissions than unamended soil in both sugarcane and rice fields. Overall, different sources of biochar affected water quality parameters differently.