Slow-release fertilizers applied in conjunction with manure enhanced soil quality and rice grain yield by regulating labile nutrient pools, soil enzyme activities, and soil structure

Context Combining slow-release fertilizers (SRFs) with organic amendments holds significant promise to increase rice yield and improve soil quality. However, there are key knowledge gaps regarding the synergistic effects of combining SRFs with different types of amendments on rice yield and soil quality. Methods A two-year field experiment was conducted to examine the effects of combining SRFs with manure or woody peat on carbon and nitrogen composition, enzyme activity, aggregate distribution, soil quality index (SQI), and rice grain yield. Results Relative to the conventional urea treatment, the use of SRFs under 15 % nitrogen reduction sustained rice grain yield and increased Nitrogen Utilization Efficiency (NUE) by 7.78–12.22 %. SRFs combined with manure significantly increased soil organic carbon (SOC) by 9.14 %, and total nitrogen (TN) by 11.82 %. It also enhanced labile carbons pools by 11.68 %–22.41 %, labile nutrients pools by 10.16 %–52.95 %, C- and N-acquiring enzyme activities by 8.21 %–38.02 %, and the proportion of aggregates > 0.25 mm (R 0.25 ) by 6.36 %–8.44 %, ultimately resulting in highest soil quality index (SQI). The rice yield increased by 7.95–13.77 %. Across all treatments, SRFs combined with woody peat exhibited the highest SOC, ROC, and DOC contents, demonstrating superior carbon sequestration efficiency. It also reduced bulk density (BD) by 8.91 %–10.69 %, and increased the proportion of aggregates > 0.25 mm (R 0.25 ) by 5.66 %–6.13 %. Random forest and Mantel’s test analyses identified labile nutrient pools (AP, AN, AHN, and DON) and enzyme activities as primary predictors of both SQI and rice yield. Conclusions SRFs can maintain rice yields and improve NUE. The combination of SRFs and manure can significantly increase soil quality and rice yield by improving nutrient supply, biological activity, and soil structure, whereas woody peat mainly contributes to soil carbon accumulation.