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