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

Abstract

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.