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.
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