Optimal fertilization strategy promotes the sustainability of rice–crayfish farming systems by improving productivity and decreasing carbon footprint

Rice–crayfish farming systems (RCs), a novel rice cropping system, have gained rapid popularity in many countries due to their economic advantages. Fertilizers tend to be applied in large quantities for higher profits, but has high burden on resources and environment, especially in terms of the carbon emissions. It is crucial to explore an optimal fertilization strategy with high productivity and low carbon emissions for the sustainable development of RCs. However, information about C emissions is incomplete, regarding the indirect C emissions during the rice growing season as well as C emissions during the crayfish culture period. We conducted field experiments to investigate the effects of five fertilization strategies including no fertilization (CK), farmer’s practices (FP), optimized fertilization (OPT), organic fertilization only (OF), and organic fertilizer substitution (OPTOF) on the productivity, economic benefits, greenhouse gas (GHG) emissions, carbon footprint, and sustainability index of RCs. Results showed that OPT reduced direct (by 6.7%) and indirect (by 37.0%) GHG emissions during the rice growing season while maintaining rice (95%) and crayfish (104%) yields compared with that of FP. Additionally, the soil organic carbon storage and annual economic benefit of the OPT increased by 20.1% and 4.7%, respectively, whereas the carbon footprints of unit area, unit grain yield, unit energy yield, and unit of economic output decreased by 29.5%, 27.2%, 24.5%, and 32.7%, compared to the FP, respectively. The sustainability index (0.78) of the OPT treatment was significantly higher than that of other treatments due to its higher productivity and lower the carbon footprint. In conclusion, optimal fertilization strategy in RCs could achieve to increase productivity while reducing carbon footprint. This is conducive to the sustainability of RCs. Future attention in RCs should be focused on the development and promotion of such strategies.