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.