Contrasting effects of rice husk and its biochar on N 2 O emissions and nitrogen leaching from Lei bamboo soils under subtropical conditions

Biochar has been widely recommended as an effective soil amendment for reducing nitrous oxide (N 2 O) emissions and nitrogen (N) leaching. However, the effects of biochar application to Lei bamboo plantations on soil N 2 O emissions and N leaching remain unclear. These effects on soil N 2 O emissions and N leaching were investigated in the present study using five treatments applied with the same amount of N: rice husk at 10 t ha −1 (10H) and 30 t ha −1 (30H), biochar at 10 t ha −1 (10B) and 30 t ha −1 (30B), and no additions (control, CK). Both the 10H and 30H treatments significantly increased cumulative N 2 O emissions compared to the CK treatment, with an increment of 0.78 and 2.20 kg N ha −1 , respectively. The 30B treatment significantly reduced cumulative N 2 O emissions by 0.90 kg N ha −1 , whereas the 10B treatment had no significant effect. The reduction in N 2 O emissions following the high-rate biochar addition was probably due to the increased pH and the total abundance of nosZ I and nosZ II genes. The 30H treatment significantly increased nitrate N (NO 3 − –N) and dissolved organic N (DON) leaching by 38% and 170% respectively compared to the CK treatment, and had the largest N loss via N 2 O emissions and N leaching, while the 30B treatment had the lowest N loss. Partial least squares path modeling revealed that soil chemical properties [ammonium nitrogen (NH 4 + –N), NO 3 − –N, DON, dissolved organic C (DOC), total N (TN), soil organic C (SOC), and pH] dominantly affected soil N 2 O emissions, while the total abundance of denitrifying genes ( nir S, nir K, nosZ I, and nosZ II) were the key factors involved in reducing NO 3 − –N leaching. There was a strong positive correlation between cumulative N 2 O emissions and N leaching loss, which may be related to excessive N surplus in the soil. Our results suggest that the replacement of rice husk by its biochar at a high-rate would reduce the risk of N 2 O emissions and N leaching loss effectively from Lei bamboo forests in subtropical China.