Converting rice husk to biochar reduces bamboo soil N2O emissions under different forms and rates of nitrogen additions

The effects of biochar application combined with different forms and rates of inorganic nitrogen (N) addition on nitrous oxide (N2O) emissions from forest soils have not been well documented. A microcosm experiment was conducted to study the effects of rice husk and its biochar in combination with the addition of N fertilizers in different forms (ammonium [NH4+] and nitrate [NO3−]) and rates (equivalent to 150 and 300 kg N ha−1 yr−1) on N2O emissions from Lei bamboo (Phyllostachys praecox) soils. The application of rice husk significantly increased cumulative N2O emissions under the addition of both NO3−-N and NH4+-N. Biochar significantly reduced cumulative N2O emissions by 15.2 and 5.8 μg N kg−1 when co-applied with the low and high rates of NO3−–N, respectively, compared with the respective NO3−-N addition rate without biochar. There was no significant difference in soil N2O emissions between the two NH4+-N addition rates, and cumulative N2O emission decreased with increasing soil NH4+-N concentration, mainly due to the toxic effect caused by the excessive NH4+-N on soil N2O production from the nitrification process. Cumulative N2O emissions recorded 18.74 and 14.04 μg N kg−1 under low and high rates of NO3−-N addition, respectively, which were higher than those produced by NH4+-N addition. Our study demonstrated that the conversion of rice husk to biochar could reduce N2O emissions under the addition of different N forms and rates. Moreover, rice husk or its biochar in combination with NH4+-N fertilizer produced less N2O in Lei bamboo soil, compared with NO3−-N fertilizer.