Effect of Biochar Amendment on Quality Parameters of Runoff and Pond Water from Sugarcane and Rice Paddy Fields.

Biochar amendment to agricultural soils has suggested for improving soil quality, enhancing soil carbon sequestration, and reducing greenhouse gas emission. However, the effect of biochar application on agricultural water quality is not yet fully understood. In this study, field experiments were carried out in sugarcane and rice fields to investigate the effect of biochar on runoff and pond water quality, respectively. For rice field experiment, commercially produced biochars from rice straw and pinewood were applied at a rate of 8960 kg/ha. For sugarcane field trials, the same rate of commercially produced biochar from sugarcane harvest residue along with different rates of pinewood biochar was applied. Runoff water samples were collected using Avalanche ISCO auto samplers at the sugarcane site whereas surface water was periodically collected from the rice site. Various soil physical and chemical properties were characterized at the beginning, during, and the end of the experiments.  Results showed that biochar application generally decreased electrical conductivity (EC) in both pond water of rice fields and runoff water from sugarcane fields. Biochar amendment tends to reduce nitrate and phosphate concentrations while increasing total organic carbon (TOC) and total suspended solids (TSS) in runoff water as compared to the control plots. Between different sources of biochars, pinewood biochar exhibited stronger retention of phosphorus than the sugarcane biochar. Overall, biochar amendment affected water quality parameters both positively and negatively.