Rice Genomics and Genetics 2025, Vol.16, No.3, 116-131 http://cropscipublisher.com/index.php/rgg 118 output, and the multi-level utilization of energy significantly improves the energy conversion efficiency of the rice field ecosystem. Studies have shown that rice-fish symbiosis can effectively recycle nutrients and energy wasted in rice field monoculture for fish production, thereby increasing the overall output rate of the ecosystem. The integrated farming system has a strong ecological regulation function. For example, the activities of ducks and fish can destroy the breeding environment of pests and diseases, inhibit the occurrence of rice blast and insect pests, and reduce the input of pesticides; the stirring of animals can promote soil aeration and nutrient mineralization, and maintain the dynamic balance of soil fertility. These ecological characteristics enable the integrated farming model of rice fields to achieve agricultural production while taking into account environmental friendliness and ecological service functions, and is known as the "micro-ecological cycle in rice fields." 2.3 Fertilization differences across models Due to the different types and densities of animals introduced, the fertilization and field management strategies of integrated farming in rice fields are somewhat different. Generally speaking, integrated farming can partially replace the application of chemical fertilizers, but different modes require reasonable adjustment of fertilizer input to avoid excess or insufficient nutrients. In rice-duck farming, since ducks mainly feed on field feed and rarely receive supplementary feeding, the amount of their feces returned to the field is limited, and generally a certain amount of base fertilizer and topdressing fertilizer still need to be applied according to soil testing formula. However, practice shows that compared with conventional rice farming, the amount of nitrogen applied to rice-duck fields can be reduced by 20% to 30%, and a comparable yield can be obtained without the application of herbicides and pesticides. Rice-fish and rice-crab models often require feeding, and the animal's food conversion rate is limited, so leftover bait and feces become an important source of nutrients in the field. This type of model can appropriately reduce the amount of chemical fertilizer application and emphasize the application of organic fertilizer or bio-organic fertilizer to cooperate with aquaculture. For example, it is recommended to reduce chemical nitrogen fertilizer by more than 50% in rice-shrimp farming fields and replace it with organic fertilizer to prevent the superposition of feed nitrogen and fertilizer nitrogen from causing nutrient excess. Xu et al. (2025) found in the Erhai Lake Basin that partially replacing chemical fertilizer with organic fertilizer can significantly reduce nitrogen and phosphorus concentrations in field water while maintaining yield in rice-duck farming fields, reducing environmental risks. Different animal species and breeding densities also affect soil nutrient management strategies. For example, Zhang et al. (2021) compared the effects of different duck breeds in the rice-duck symbiotic system and found that local duck breeds with strong adaptability had more obvious improvements in soil physical and chemical properties, and higher rice yields and economic benefits. Too high density may lead to excessive nutrient accumulation and oxygen debt, aggravating soil reduction, and need to be carefully controlled. Ni et al. (2022)'s survey showed that in Hubei Province, when the area of the breeding ditch dug for shrimp farming in rice fields accounted for more than 20%, the rice yield decreased significantly, indicating that excessive breeding intensity may weaken the planting benefits. Therefore, for different integrated breeding modes, it is necessary to optimize the fertilization system, such as adjusting the ratio of base and topdressing, increasing the application of organic fertilizers and slow-release fertilizers, etc., to adapt to the nutrient supply and demand characteristics of the breeding system and achieve a dynamic balance between nutrient input and output. 3 Effects on Soil Nutrient Content 3.1 Organic matter accumulation and humus enrichment Integrated farming in rice fields is generally observed to increase soil organic matter content and improve soil humus levels. The main reason is that animal feces, bait residues and aquatic organism remains are continuously returned to the soil, supplementing exogenous organic matter. Compared with conventional rice fields, the soil organic carbon content of integrated farming rice fields is usually significantly higher. For example, Li et al. (2025) found in a field experiment in Zhejiang that compared with single-season rice, rice-fish farming can increase the organic carbon of the surface soil by 4.8%~13.6% (2-year and 5-year farming); when the farming lasts for more than 15 years, the increase in soil organic carbon is as high as 23%~32%. Another study in Hunan also showed that long-term rice-fish symbiosis can increase the organic matter content of rice field soil by 18%~42% compared with single farming. Rice-duck farming also significantly accumulates organic matter. Lan et al. (2021) reported
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