Converting rice husk to biochar reduces bamboo soil N 2 O 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 (N ₂ O) 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 [NH ₄ ⁺ ] and nitrate [NO ₃ ^- ]) and rates (equivalent to 150 and 300 kg N ha ^-1 yr ^-1 ) on N ₂ O emissions from Lei bamboo (Phyllostachys praecox) soils. The application of rice husk significantly increased cumulative N ₂ O emissions under the addition of both NO ₃ ^- -N and NH ₄ ⁺ -N. Biochar significantly reduced cumulative N ₂ O emissions by 15.2 and 5.8 μg N kg ^-1 when co-applied with the low and high rates of NO ₃ ^- -N, respectively, compared with the respective NO ₃ ^- -N addition rate without biochar. There was no significant difference in soil N ₂ O emissions between the two NH ₄ ⁺ -N addition rates, and cumulative N ₂ O emission decreased with increasing soil NH ₄ ⁺ -N concentration, mainly due to the toxic effect caused by the excessive NH ₄ ⁺ -N on soil N ₂ O production from the nitrification process. Cumulative N ₂ O emissions recorded 18.74 and 14.04 μg N kg ^-1 under low and high rates of NO ₃ ^- -N addition, respectively, which were higher than those produced by NH ₄ ⁺ -N addition. Our study demonstrated that the conversion of rice husk to biochar could reduce N ₂ O emissions under the addition of different N forms and rates. Moreover, rice husk or its biochar in combination with NH ₄ ⁺ -N fertilizer produced less N ₂ O in Lei bamboo soil, compared with NO ₃ ^- -N fertilizer.