Co-benefits of reduced carbon and water footprints and enhanced carbon sequestration with integrated organic–inorganic fertilization and cover cropping in hilly citrus orchards

Citrus, a globally significant fruit crop, is predominantly cultivated on sloping land in China with a large amount of resource input and incurs high environmental costs. Current research often relies on general parameters and rarely simultaneously assesses carbon footprint (CF) and water footprint (WF) to reveal the synergistic effects in emission reduction strategies. To address knowledge gaps, we conducted a 2-year county-scale survey and a 3-year field experiment in Zhongxian County, Chongqing, China. We optimized five nutrient management schemes, chemical fertilizer (Che), chemical fertilizer + organic manure (Che+Org), chemical fertilizer + cover crops (Che+CC), chemical fertilizer + organic manure + cover crops (Che+Org+CC), and optimized management (OPT), and analyzed them using the life cycle assessment (LCA) framework. The results showed that OPT achieved dual benefits of high productivity and low carbon-water cost, with a CF reduction of 26.9%-64.6% and a WF reduction of 75.7%-92.1% compared with other treatments. Nitrogen fertilizer production and application were the primary CF sources, whereas cover crop integration markedly decreased WF. A significant positive correlation between CF and grey WF (<i>p</i> < 0.05) indicates that cover crops simultaneously mitigated carbon emissions and reduced nitrogen/phosphorus runoff. While achieving these environmental benefits, the citrus yield of the OPT was 33.57% higher than that of the Che, and the economic returns were 45.51% higher. This study demonstrates that in the sloping land environment, selectively combining organic fertilizers and cover crops can transform the contradiction between yield and the environment into a synergistic effect, thereby deepening the understanding of sustainable nutrient management. The research results show that the OPT system is a superior nutrient management strategy for sloping citrus orchards. The research results also provide reliable and specific evidence to support the optimization of the "organic substitution" policy and offer a feasible approach for low-carbon, high-efficiency citrus production in ecologically fragile regions.