Balancing carbon sequestration and emissions: Granulated organic amendments enhance ecosystem-economic benefits in subtropical infertile paddy fields

The sustainable rehabilitation of infertile paddy fields is critical for improving food security and reducing agricultural greenhouse gas (GHG) emissions in subtropical regions. However, the carbon and economic trade-offs associated with applying granulated organic amendments remain unclear. A two-year field experiment was conducted in subtropical China to evaluate the ecological and economic impacts of deep plowing with granulated organic amendments in an infertile paddy soil. Four treatments were compared: chemical fertilizer only (CF), composted manure (CM, 10 t ha -1 yr -1 ), low-rate granulated amendment (LG, 20 t ha -1 ), and high-rate granulated amendment (HG, 40 t ha -1 ). The composted manure was applied annually in both years, whereas the granulated organic amendment was applied only once at the beginning of the two-year experiment. Compared to CF, the LG treatment maintained similar CH 4 and CO 2 emissions, reduced net greenhouse gas emissions (NGHGE) and net greenhouse gas intensity (NGHGI), while enhancing soil organic carbon sequestration rate (SOCSR) and residue carbon conversion efficiency (RCCE). Moreover, LG increased net ecosystem carbon budget (NECB) by 322% and improved net ecosystem economic benefit (NEEB) by 0.82%. Although the HG treatment achieved greater NECB, it was less cost-effective due to higher input costs and increased emissions. Functional gene analysis revealed that shifts in methanogenic and methanotrophic gene abundance were linked to nutrient dynamics and GHG fluxes. Overall, moderate application of granulated organic amendments (20 t ha -1 ) improved soil carbon storage, mitigated emissions, and enhanced agroecosystem profitability in infertile paddy fields. This practice aligns with climate-smart and circular agricultural principles, providing a feasible improvement strategy for the infertile paddy field systems in subtropical regions. • Moderate input of granulated amendments enhanced C conversion efficiency. • Optimizing granulated amendment rate could reduce NGHGE and improve ecosystem economic benefits. • Suitable granulation strategies offer a resource-efficient pathway for sustainable intensification of infertile rice fields.