Mechanism of biochar on nitrification and denitrification to N₂O emissions based on isotope characteristic values

To clarify the mechanism of biochar on nitrification and denitrification to N₂O emissions in farmland soil, the effects of combined application of biochar and different nitrogen sources on the contributions of nitrification and denitrification to N₂O emissions were studied using isotope characteristic values. The results showed that the soil N₂O emissions from ammonium nitrogen fertilizer treatments were significantly higher than that from nitrate nitrogen fertilizer treatments. The biochar combined with ammonium nitrogen fertilizer reduced soil N₂O emissions by 31.0%-30.8%, and biochar combined with nitrate nitrogen fertilizer reduced soil N₂O emissions by 70.6%-63.0%. The isotope model showed that the application of ammonium nitrogen fertilizer was more favorable for soil nitrification in the early stage of the experiment (0-2 d), and more favorable for denitrification in the middle and later stages of the experiment (3-17 d). Application of nitrate nitrogen fertilizer enhanced the nitrification of soil nitrifying bacteria in the early and middle stages of the experiment (0-8 d), and the denitrification of soil denitrifying bacteria in the later stage of the experiment (9-17 d). The effects of biochar on N₂O emissions were mainly in the middle and later stages of the experiment by promoting the nitrification of nitrifying bacteria and inhibiting denitrification of denitrifying bacteria, so as to reduce N₂O emission in soil. These results may help to understand the mitigation mechanism of biochar on N₂O emission in upland soil.