Co-Incorporation of Green Manure and Rice Straw Increases Rice Yield and Nutrient Utilization

The co-incorporation of green manure and rice straw is commonly used to increase rice yield and improve soil fertility in paddy fields. However, the effects on nutrient uptake and utilization of rice under the synergistic interaction mechanism in the Taihu Plain of the Yangtze River Delta remain unclear. Based on field experiments, this study investigated the effects of green manure with rice straw return (GMS) under different nitrogen (N) fertilization rates on rice yield, nutrient use efficiency, and soil fertility. The results revealed that green manuring significantly increased rice yield while improving the uptakes and use efficiencies of N, phosphorus (P) and potassium (K). Green manure (GM) with 40% N fertilizer reduction (GM_N60) maintained the grain and straw yields and nutrient uptakes compared to winter fallow with 100% conventional N application (WF_N100). The N recovery efficiency in GM_N60 reached 45.52%, increasing by 41.26% compared to WF_N100. Rice yield and K uptake in the GMS with 40% N fertilizer reduction treatment (GMS_N60) was 10,058 and 15.41 kg/hm², increasing by 14.43% and 9.43% compared to winter fallow with rice straw return and 100% conventional N (WFS_N100). The N, P and K agronomic efficiencies in GMS_N60 increased by 77.04%, 50.22%, and 50.22% compared to WFS_N100, respectively. These findings indicate that rice straw return enhances the fertilizer-saving and yield-increasing effects of GM, promotes rice K uptake and improves P and K use efficiencies. The GM treatment increased the soil organic matter (SOM), total potassium (TK), ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) contents. Among the soil fertility indicators, TK and SOM were the most important factors influencing rice yield and N uptake. In conclusion, GMS can maintain or increase rice yield with 40% N fertilizer reduction, improve nutrient use efficiencies, and increase the reuse of rice straw, thereby supporting green and efficient rice production in the southern Jiangsu paddy area.