Nutrient management regulates soil fertility in paddy–upland rotations: A meta-analysis

Maintaining soil fertility through balanced fertilization is essential for ensuring high crop productivity in intensive paddy-upland rotation systems. In this study, a meta-analysis of 141 published studies was conducted to evaluate the effects of different fertilization regimes on soil chemical properties and crop yields in predominant paddy-upland rotation systems. Relative to balanced fertilization (BF), both no fertilization (CK) and unbalanced fertilization (UF) significantly reduced soil organic matter (SOM) (16.6% and 7.2%), total N (11.3% and 4.9%), total P (14.6% and 7.1%), available P (41.0% and 22.9%), and available K (13.0% and 11.0%). In contrast, the combined application of chemical fertilizer with organic manure (F+M) or straw return (F+S) significantly increased SOM (16.5% and 9.6%), total N (14.9% and 8.7%), total P (29.2% and 16.6%), available P (37.6% and14.7%), and available K (9.1% and 12.9%). Notably, the response of soil fertility to fertilization regimes differed between oilseed rape–rice (OR) and wheat–rice (WR) rotations. The WR rotation showed greater declines in SOM and total N under CK treatment than the OR rotation. While F+S treatment was more effective in improving soil available P in OR rotation, F+M treatment produced better outcomes in WR rotation. These soil responses were reflected in crop yields, with a more severe rice yield reduction under CK in the WR (45.0%) than in the OR rotation (29.2%). The greatest yield increases were associated with the F+S treatment in OR and the F+M treatment in WR. Random Forest analysis and linear regression identified SOM, available P, and total N as the primary factors governing rice yield. These results suggest that integrated nutrient management combining chemical fertilizers with organic amendments is crucial for sustaining soil fertility and productivity in paddy-upland rotations, and that tailored fertilization strategies should be developed based on specific rice-based cropping systems.