Biochar effects on soil chemical properties and mobilization of cadmium (Cd) and lead (Pb) in paddy soil

This study focused on the effects of biochar (BC) application on soil chemical properties and mobilization of cadmium (Cd) and lead (Pb) in the paddy soil. BC was applied at the rate of 0, 10, 20 and 40 t ha(-1), respectively. BC application caused a significant increase in soil organic carbon contents (SOC), pH, nitrate-nitrogen (NO3--N),and available phosphorus contents (AP) in the top and subsurface soil, while SOC contents in the subsurface soil decreased with increasing rate of BC. BC40 effectively reduced the mobility of Cd and Pb from the top layer to the subsurface soil, while concentrations of Cd and Pb in the topsoil remained unchanged. Path analysis showed that the direct path coefficient AP was highest; SOC, NH4+-N and AP had a negative direct effect on the Cd and Pb in subsurface soil. Soil pH and NO3--N had a high negative indirect effect through AP. The decision coefficient decreased in the following order: pH, AP, SOC, NH4+-N and NO3--N. Regression analysis showed that soil Cd and Pb had a significant linear correlation with soil AP, whereas soil Pb also had a significant linear correlation with soil pH. In conclusion, BC40 can alter soil chemical properties and reduce the mobility of Cd and Pb from the top layer to the lower subsurface of the paddy soil.