Rice Genomics and Genetics 2025, Vol.16, No.3, 116-131 http://cropscipublisher.com/index.php/rgg 124 of farmland far exceed that of single planting. From the perspective of soil nutrient management, this model improves soil organic matter and nitrogen and phosphorus levels through duck manure, providing fertile soil for saffron growth, while the decomposition of saffron residues replenishes soil organic matter, achieving a virtuous cycle. The practice of Xingqing Farm has proved that the integrated breeding model can be adapted to local conditions and rotated with efficient cash crops, which not only maintains the health of the rice field ecosystem, but also creates considerable benefits. It has been rated as a typical case of innovative breeding model by the Ministry of Agriculture and Rural Affairs for promotion and reporting (Xu et al., 2017; Gao et al., 2025). This case reflects the huge potential of "rice field+aquatic products+cash crops" compound management, and provides a demonstration for family farms to increase land output and achieve green income. Figure 2 Rice-duck farming system (Photographed by Yuchao Shen) 5.2 Improvement of acidic soils under rice–fish co-culture The soil in some southern rice-growing areas is acidic and heavy, which often leads to reduced rice production. The rice-fish co-cultivation model shows a unique role in improving acidic soil. In the red soil rice fields (pH≈5.5) of the Hunan experimental site, loaches and crucian carp were introduced to carry out rice-fish symbiosis. After three years of continuous cultivation, the soil pH value rose to about 6.2, effectively buffering the acidity. According to analysis, the reasons for the reduction in soil acidity are: first, fish excrement contains alkaline ions such as calcium and magnesium, which neutralize part of the acidity; second, the water-reducing and oxygen-reducing environment of the rice-fish field inhibits acid-producing processes such as sulfate reduction; third, the increase in organic matter and humification increase the soil buffering capacity, reducing pH fluctuations (Zhou et al., 2024). Guo et al. (2020) also pointed out that the soil nutrients in the rice-fish system are sufficient and can increase pH, which is conducive to the improvement of acidified soil. In addition to pH, rice-fish symbiosis also improves other physical and chemical properties of acidic soil. A comparative experiment in Fujian showed that after fish farming in rice fields, the exchangeable aluminum in the soil was significantly reduced, while the content of effective phosphorus and potassium increased, the soil particle structure improved, and the tillage layer changed from compacted to loose. This shows that rice-fish farming can alleviate adverse factors such as aluminum toxicity and nutrient fixation in acidic soils through bioturbation and nutrient cycling. A typical case comes from the acidic field improvement project in Guangxi: the local introduction of rice-fish farming combined with lime improvement increased the soil pH from 4.8 to 5.6 within two years, and the rice yield per unit area increased by 15%, proving the effectiveness of the rice-fish model in improving acidic low-yield fields. Of course, it should be noted that the effect of rice-fish farming on soil pH is gradual and limited, and lime and other conditioners are still needed to fundamentally improve strong acidic soils. However, the rice-fish model can at least partially alleviate the harm of soil acidification and provide a more friendly soil environment for crops.
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