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To study whether integrative fertilization [growing milk vetch in winter and reducing the dose of chemical nitrogen (N) fertilizer] can improve rice yield, and to reveal the underlying regulatory mechanisms for integrative fertilization, a three-year field trial including two treatments, milk vetch-rice-rice (MRR) and winter fallow-rice-rice (FRR), was conducted in 2010, 2011 and 2012. Our results demonstrated that the MRR treatment could significantly improve rice yield compared with the FRR treatment, especially when the application ratio of milk vetch and chemical fertilizer was 1:2. MRR treatment increased the effective panicle number and the spikelet number per panicle. In addition, a higher tillering number, leaf area index, photosynthetic-potential and photosynthetic-potential to grain ratio were observed in MRR treatment, which could provide enough dry matter for yield formation. Moreover, in MRR treatment, we discovered a higher transportation ratio and transformation ratio of dry matter in culm and leaves, and a stronger total sink capacity and spikelet-root bleeding intensity at the heading stage and 15 d after heading. Furthermore, the MRR treatment showed higher total N, phosphorus and potassium uptakes than FRR treatment, which was associated with the higher root dry weight in each soil layers. These results suggest that growing milk vetch in winter can improve rice yield under less chemical N fertilizer application, which is due to the improvement of soil nutrient status and the increased of rice root growth and development.

Crop residue management affects both crop productivity and soil fertility as well as human and environmental health, thus playing a critical role in the sustainability of cropping systems. We conducted a meta-analysis to examine the effect of in situ retention of crop residues on rice yield in China, and evaluated their fertilizer value for rice production. Results indicated that overall, crop residue retention significantly increased rice yield by 5.2% in China. Spikelet number per panicle and grain weight showed significant positive responses to crop residue retention, whereas the number of panicles and the percentage of filled grains were not significantly affected. Yield gains under crop residue retention were lowest, but significant, at mean annual temperature of 11–15 °C. Yield responses to crop residue retention were not significantly affected by soil N content, residue types (legume vs. non-legume), and tillage regimes (no-tillage vs. conventional tillage). Rice yield gains under crop residue retention increased with increasing experimental duration. Yield responses to crop residue retention increased when the proportion of inorganic N fertilizer applied in the vegetative stage increased from 70% to 100%. Compared to full rates of inorganic fertilization alone, rice yield was not adversely affected by crop residue retention with reduced rates of inorganic N, P, and K fertilizers by averages of 29.4%, 8.3%, and 21.9%, respectively. Therefore, we conclude that crop residue retention can significantly increase rice yield and substitute a part of inorganic fertilizers, while the magnitude of yield gains and fertilizer reduction may be site-specific and depend on agronomic practices.