Partial organic substitution for synthetic fertilizer improves soil fertility and crop yields while mitigating N2O emissions in wheat-maize rotation system

Excessive synthetic N fertilization has resulted in severe soil degradation and high greenhouse gas emissions in agroecosystems. As a promising approach for achieving sustainable agriculture, partial organic substitution for synthetic fertilizer can affect the stoichiometric balance between organic C and inorganic N, thereby regulating nitrous oxide (N2O) fluxes. However, the responses of soil N2O emissions and crop productivity to different ratios of organic fertilizer (OF) to synthetic fertilizer (SF) are still unclear, making the optimal fertilization scheme less accurate. A 2-year field experiment was conducted to measure soil properties, N2O emissions, and crop yields in a wheat-maize rotation system. Six fertilization managements were included: no fertilization (CK); total SF; and 15%, 30%, 45%, and 100% of organic substitution for synthetic fertilizers (LO, MO, HO, and OF), respectively. Compared to SF, soil annual cumulative N2O emissions in LO, MO, HO, and OF were significantly reduced by 16.2–20.5%, 28.9–33.9%, 33.2–42.2%, and 70.2–74.9% in two years, respectively. The mitigation of N2O emission with organic substitution was mainly attributed to the decreasing NO3- and NH4+ contents and increasing soil pH. Meanwhile, soil organic C and total N were considerably higher in HO and OF than other treatments, with the lowest in CK in wheat season and in SF in maize season. Synthetic fertilizer and partial organic substitution increased the annual yield of wheat and maize compared with OF and CK in the first year, and HO increased the annual yield by 9.7% and 37.6% compared with SF and OF in the second year, respectively. The beneficial yield effects were mainly due to the enhanced synchronization of nutrient availability and soil fertility with partial organic substitution. Finally, the yield-scaled N2O emissions were reduced with increasing ratios of organic substitution in two years. Our study suggested that partial organic substitution for synthetic fertilizer, especially 45% organic substitution would be feasible fertilization strategy to improve soil fertility and crop productivity while mitigating N2O emissions in wheat-maize rotation systems.