Biochar mitigated more N-related global warming potential in rice season than that in wheat season: An investigation from ten-year biochar-amended rice-wheat cropping system of China

Rice-wheat cropping system (RWCS), the major rice-based cropping system, constitutes a significant source of N-related greenhouse gas (GHG) emission due to the unique wet-dry alternation process. Biochar is often highlighted as a potential solution for reducing fertilizer N losses, hence, understanding its effects on Ngr emissions (mainly NH3 and N2O) under wet-dry conditions is critical to inform strategies for GHG mitigation. This study investigated the responses of NH3 and N2O emissions to biochar amendments during rice and wheat seasons based on in situ measurements under ten-year successive straw biochar application in RWCS. Our results indicated that 43.7% and 89.9% of N2O and NH3 emissions were emitted during rice season and 56.3% and 10.1% during wheat season, respectively. Long-term biochar amendment was found to play significant role in mitigating NH3 emissions (38.6-43.9%), which could be attributed to the disappearance of liming effect of aged-biochar on flooding water and decreased NH4+ concentrations in the soil. However, considerable variation of N2O emissions were observed in RWCS. Biochar showed a significant decreasing effect on the net global warming potential related to N2O and NH3 emissions (GWP(N)) in rice season (16.1-89.6%), and slight increased tendency in wheat season (1.43-13.1%) primarily due to its positive effects on N2O emission. Biochar amendment mainly BC22.5, significantly increased above-ground yields by 9.22% in rice season. Thus, it is a low carbon-producing and sustainable crop management method that can support crop production, C sequestration, and GHG mitigation in rice season under RWCS from the viewpoint of the Ngr mitigation. Our results suggest that emission patterns of N2O and NH3 varied with wet-dry alternation under the disturbance of long-term biochar amendment in RWCS; moreover, long-term biochar application exhibited significant potential for mitigating soil Ngr losses in rice season for RWCS.

Automated summary

This study investigates the effects of biochar amendments on NH3 and N2O emissions during rice and wheat seasons. The results showed that long-term biochar amendment can significantly reduce NH3 emissions, but the effects on N2O emissions vary.