Abstract: Clarifying the kinetic characteristics of decomposition, carbon and nitrogen release of different winter green manures under the combined applications of organic and inorganic fertilizers can provide a theoretical basis for the efficient utilization of green manure resources and nutrient management strategies in rice cultivation in southern China. Under pot conditions, a nylon bag mesh method was used to examine the substitution of varying amounts of chemical nitrogen fertilizers with different green manures in rice paddies. The experiment involved replacing 25%, 50%, 75%, and 100% of chemical nitrogen fertilizers with aboveground parts of Chinese milk vetch, ryegrass, and rape while maintaining total nitrogen levels. Green manure residues were collected in nylon mesh bags on 0, 14, 24, 29, 34, 42, 48, 55, 69, 83, 111, 139, 167, and 192 days for analysis of dry matter decomposition, carbon and nitrogen release characteristics using the two-pool model. The results showed that the dry matter decomposition, carbon and nitrogen release exhibited a rapid initial phase, followed by a subsequent slow phase. On day 34 after decomposition, 81.9%-85.2%, 82.1%-84.3% and 61.2%-70.6% of dry matter decomposition amount was observed for Chinese milk vetch, ryegrass, and rape, respectively. At 34-192 days of decomposition, 11.8%-14.4%, 11.5%-13.4% and 14.9%-21.9% of dry matter decomposition amount was observed for Chinese milk vetch, ryegrass, and rape, respectively. Specifically, Chinese milk vetch and ryegrass exhibited relatively higher decomposition rates of dry matter, carbon, and nitrogen under the 25% replacement treatment, while rape showed higher rates under the 50% replacement treatment. Further analysis using the two-pool model showed that Chinese milk vetch and ryegrass had higher decomposition rates of dry matter, carbon and nitrogen than rape, and Chinese milk vetch exhibiting the highest decomposition rates of dry matter and nitrogen under the 25% replacement treatment, with a rate of 0.15% per day for both. The C/N ratio was negatively correlated with the decomposition of green manures, and carbon and nitrogen release. In summary, Chinese milk vetch demonstrated superior performance in decomposition and nutrient release, particularly under the 25% replacement rate.

Key words: green manure, paddy, decomposition rate, nutrient release, carbon/nitrogen ratio