Effects of Cow Dung Biochar Amendment on Adsorption and Leaching of Nutrient from an Acid Yellow Soil Irrigated with Biogas Slurry

A laboratory-scale study was conducted to test whether biochar from cow dung as a soil amendment can reduce nutrient leaching from soil irrigated with biogas slurry. Polyvinyl chloride (PVC) columns were packed with soils containing 0, 20, and 40 g kg(-1) of biochar. The biogas slurry was applied at 0, 200, and 400 ml per column, equivalent to 0, 130, and 260 kg N ha(-1). The biogas slurry was diluted to 1,500 ml with water and then applied five times every 6 days at 300 ml each time. All leached solutions were collected separately. Results showed that soil available phosphorus (P) and potassium (K) increased significantly with increased biogas slurry rates and biochar rates. The concentrations of total N, P, and K in leached solutions increased significantly as biogas slurry rates increased. Biochar significantly increased the concentrations of total and available P, total K, and electric conductance in leached solution. Contributions of biochar and biogas slurry treatments to the net amount of N, P, and K in leached solution increased with increased biochar and biogas slurry rates except at 4 % biochar rate where total N was decreased. Nutrient removal rate of biochar was over 10.6 % for total N and negative for total K at 2 % biochar rate. Nutrient removal rate of biochar was over 7.19 % for total P and negative for total N and total K at 4 % biochar rate. It is suggested that both biogas slurry and biochar have the potential to pollute water when leaching happens although biochar has the ability to adsorb N and P from biogas slurry.