Nature-based accumulation of organic carbon and nitrogen in citrus orchard soil with grass coverage

Grass coverage in orchards has increasingly become a sustainable practice to improve soil quality, reduce soil erosion, increase water infiltration, and enhance biodiversity and ecosystem services. It is likely to gain further adoption as a promising nature-based measure to increase organic carbon and nitrogen storage in soil. However, there is still a lack of comprehensive global quantification regarding the accumulation and availability of soil organic carbon (SOC) and total nitrogen (STN) after grass coverage in citrus orchards. A global meta-analysis was conducted to comprehensively evaluate the effects of grass coverage on SOC and STN dynamics in citrus orchards, as well as the patterns influenced by various factors. Compared to clean tillage, the accumulation rates of SOC and STN were significantly enhanced with grass coverage, with an increase of 19.98 Mg ha⁻¹ yr⁻¹ and 2.27 Mg ha⁻¹ yr⁻¹ , respectively. The microbial biomass carbon (MBC), dissolved organic carbon (DOC) and available nitrogen (AN) exhibited significantly increases following grass coverage, with average enhancements of 13.90 %, 17.94 %, and 18.04 %, respectively. The primary factors influencing the variation in SOC and STN were identified as grass age and growth modes. When grass coverage reached or exceeded 10 years and was applied uniformly across the entire orchard (full coverage), there was a more pronounced increase in SOC and STN levels. The present study provides policymakers and orchard managers with science-based evidence to guide adaptive management practices that enhance SOC and STN stocks, improve soil conditions, and increase orchard resilience to climate change.