Rice Genomics and Genetics 2025, Vol.16, No.3, 116-131 http://cropscipublisher.com/index.php/rgg 127 the soil nutrient pool is enriched, which can provide more abundant nutrient supply for continuous farming, thereby improving the sustainability of production. For example, in the aforementioned 10-year rice-duck experiment in Jiangxi, the total nitrogen and organic matter content of paddy soil increased slightly year by year, and in the tenth year it increased by about 15% compared with the initial value, while the control monoculture field decreased by about 5%. The enhancement of soil nutrient reserves provides a nutrient buffer for the sustained and stable yield of rice. When encountering years with reduced external inputs or unfavorable climate, the integrated farming field can still maintain a good yield due to its high soil fertility and has a stronger ability to resist stress and maintain stable yield. On the other hand, integrated farming improves the utilization efficiency of nutrient inputs. The meta-analysis of Chen et al. (2024) showed that compared with monoculture, the nitrogen fertilizer partial productivity of rice-fish/duck co-cultivation systems increased by an average of 10% to 20%, which means that more rice is produced per unit of nitrogen application. Nutrients circulate at multiple levels within the system, reducing losses and waste. In addition, the plant-animal dual-channel absorption of nutrients allows some nutrients that were originally not absorbed and utilized by rice to be transformed into forms after being utilized by animals and then absorbed by rice. For example, some organic phosphorus and algae nutrients are excreted in inorganic form after being ingested by fish, but are absorbed by rice, which indirectly improves the efficiency of nutrient utilization. For another example, in rice-duck farming, ducks eat weeds, which reduces the competition between weeds and rice for fertilizer, and improves the efficiency of fertilizer nutrients used to increase rice production. It can be said that integrated farming converts more soil nutrients into useful agricultural products rather than ineffective losses or harmful accumulation. In the long run, this efficient and cyclical soil nutrient management model helps to maintain the balance of soil nutrient income and expenditure and avoid "overdraft" of soil fertility. Admittedly, the degree to which integrated farming improves nutrient efficiency varies in different regions and models, and specific evaluation and optimization are required. For example, in black soil areas with high fertility, the advantages of integrated farming may be mainly reflected in reducing environmental loads, while in poor soil areas, its effect of improving nutrient utilization is very significant. Therefore, the integrated farming plan should be designed according to local soil nutrient conditions to maximize its function of enhancing soil nutrient reserves and utilization efficiency. 6.3 Soil health as a foundation for green agriculture Healthy soil is the foundation of green sustainable agriculture, and integrated rice farming has laid a good foundation for the development of green agriculture by improving soil health properties. First, integrated farming restores and improves the biodiversity and ecological functions of the soil. Soil health not only refers to rich nutrients, but also requires an active biosphere and a good structure. Integrated rice farming has greatly increased the richness of soil microbial populations and soil animal communities. For example, in the rice-duck model, field organisms such as spiders and frogs have increased significantly, and the soil food web structure has become more complex, which has improved the stability of the soil system from an ecological perspective. This biodiversity gives the soil a stronger self-regulation ability and is more resilient in the face of diseases or environmental stress. Secondly, the comprehensive improvement of soil physical and chemical properties has brought rice fields closer to the standard of "healthy soil". Healthy soil usually means sufficient organic matter, good aggregate structure, moderate acidity and alkalinity, and no accumulation of harmful substances. Integrated farming practices have shown that after several years of fish-duck farming in rice fields, the aggregate structure of the soil tillage layer has been significantly improved, the porosity has increased, the organic matter has increased, and the heavy metal and pesticide residues have been significantly reduced (Huang, 2024). Studies have shown that the total salt content of soil in long-term rice-fish farming fields has decreased by more than 20%, the pH has tended to be neutral, and the organic matter has increased by 2-3 percentage points. These
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