Nutrient release regulation of stubble in the Italian ryegrass–rice rotation (IRR) system

The dynamic release of nutrients from rice (Oryza sativa) and Italian ryegrass (Lolium multiflorum) stubble was studied to explore the soil fertilization mechanisms in the Italian ryegrass–rice rotation (IRR) system. The results showed that the fastest degradation of rice and Italian ryegrass stubble occurred during the first 30 days: 19.12% of rice stubble and 38.89% of Italian ryegrass stubble degraded during this period. The degradation rate of rice stubble showed a tendency of first decrease and then increase with the change in air temperature. The degradation rate of Italian ryegrass stubble decreased significantly at an increasing temperature in summer. The release rate of nitrogen, phosphorus, and potassium in Italian ryegrass was significantly faster than that of rice (P < 0.05) during the rotation period. The release rate of calcium and magnesium in rice was significantly faster than that of Italian ryegrass (P < 0.05). Soil analysis before and after degradation showed that the total nitrogen content of rice degraded soil was significantly higher than that of the control soil (before degradation) (P < 0.05). The total nitrogen content of Italian ryegrass degraded soil was the highest, and significantly higher than after rice degradation (P < 0.05). Soil total phosphorus content decreased with the degradation of rice and Italian ryegrass stubble, but there was no significant difference with the pre-degradation content (P > 0.05). Soil total potassium content increased after the rice stubble degradation (P < 0.05) but decreased after the Italian ryegrass stubble degradation (P < 0.05). The results demonstrate the nutrient release mechanisms of two kinds of stubble and their effect on the soil nutrient content during rice and Italian ryegrass rotation. This study can provide theoretical support for fertilization methods in the Italian ryegrass–rice rotation system.