Effects of biochar application on the loss characteristics of Cd from acidic soil under simulated rainfall conditions

Biochar is widely used for immobilizing heavy metals in soil as a kind of high-effective passivator. This research conducted incubation and simulated rainfall experiments to study the effects of biochar application on the loss characteristics of runoff and sediment, as well as the transportation of the Cd during the water erosion process. Two rainfall intensities (60 and 120 mm h^-1) and five biochar application rates (0%, 1%, 3%, 5%, and 7%) were considered in the experiment. The result showed that slaking had a greater effect than mechanical stirring in aggregate breakdown of the soil, and the addition of biochar generally increased the sensitivity of the soil to wet stirring, while had no obvious influence on the resistance to slaking. The H₂O and CaCl₂ extractable Cd in soil significantly decreased with the increase of biochar application rate. The runoff yields decreased with the increase of biochar application rate at both the two rainfall intensities, while the eroded sediment generally decreased at the 120 mm h^-1 rainfall intensity. The addition of biochar tended to increase the loss of the middle-sized (1-0.05 mm) aggregates at the 60 mm h^-1 rainfall intensity, whereas reduced their loss at the 120 mm h^-1 rainfall intensity. Biochar application could significantly reduce the concentration of Cd in the runoff and decreased the total loss amount of Cd (sediment+runoff) in most of the cases. Excessively high level (7%) of biochar application may aggravate soil erosion and result in more Cd loss.