Lowering nitrogen inputs and optimizing fertilizer types can reduce direct and indirect greenhouse gas emissions from rice-wheat rotation systems

Agriculture soil is one of major sources of greenhouse gas (GHG) emissions. A wise use of nitrogen (N) fertilizer is important for mitigating GHG emissions. To evaluate the potential of different fertilizers treatments to mitigate total GHG emissions, a field experiment was conducted to investigate nitrous oxide (N2O), methane (CH4) and ammonia (NH3) emissions and nitrate (NO3-) leaching from a typical rice and winter wheat rotation system in Southeast China. Six reduced N treatments (including single reducing N input, increasing potassium input, combined application of urea ammonium (UA) and organic fertilizer (OF), single application of urea with hydroquinone and dicyandiamide (UHD) and urea formaldehyde (UF)) and the local practice (conventional N fertilizer) were applied in the study. Most of the reduced N treatments tended to reduce the cumulative CH4, N2O and NH3 emissions and NO3- leaching relative to the local practice, while single application of UHD during the rice season obviously increased the CH4 and NH3 emissions (p < 0.05) and all of the reduced N treatments during the wheat season had no obvious mitigation effect on NO3- leaching. Moreover, the single reducing N input and single application of UHD significantly decreased the rice yields (p < 0.05), and the other treatments could maintain the yields. For the whole rice-wheat rotation system, only the single application of UHD significantly increased the GHG intensity (GHGI) by 22.0% (p < 0.05) and reduced the N use efficiency (NUE) by 9.1% compared to the local practice and the other reduced N treatments reduced the GHGI by 11.0-42.7% and increased the NUE by 5.2-34.3%, especially the reducing local N input levels by 18-32% and increasing potassium input or combined application of UA and OF treatments, which had the obvious mitigation effects and should be given priority for total GHG mitigation in future crop production.