Rice Genomics and Genetics 2025, Vol.16, No.3, 116-131 http://cropscipublisher.com/index.php/rgg 119 that the soil organic carbon in rice-duck symbiotic fields increased by about 10% compared with conventional rice fields, indicating that the addition of duck manure and aquatic biomass effectively supplemented the soil organic matter. Under the conditions of integrated farming, the composition of soil humus also tends to be optimized. A study found through infrared spectroscopy that the proportion of humus components such as humic acid and fulvic acid in rice-shrimp symbiotic soil increased, indicating that the quality of soil organic matter has improved (Xu et al., 2025). Humus is the cornerstone of soil fertility, and its increase helps to improve the soil's water and fertilizer retention capacity and buffering performance. It is worth noting that the large accumulation of organic matter mostly occurs in the 10 cm~20 cm soil layer on the surface of the rice field, which is related to the fact that animal activities and residues are mainly distributed in the surface layer. Therefore, how to evenly mix the accumulated organic matter in the surface layer into the deep layer through appropriate tillage measures is also one of the issues that need to be paid attention to in the management of integrated farming soil. 3.2 Dynamics of macronutrients: nitrogen, phosphorus, potassium The impact of integrated rice farming on the content of nitrogen (N), phosphorus (P) and potassium (K) in the soil is relatively complex. The overall trend is that the total nutrients in the soil increase, and the level of available nutrients changes dynamically during the growth period and is higher than that of the single-crop control. In terms of nitrogen, due to the nitrogen content of animal excrement, the total nitrogen content of the soil in integrated farming fields is often higher than that in conventional rice fields. According to the experiment of Li et al. (2020), the system of mixed planting of multiple varieties of rice combined with rice-duck farming increased the total nitrogen content of the soil by 4.3%~17.9% in the mid-season compared with single planting, and the soil alkaline nitrogen increased by 4%~18%. Yan et al. (2023) compared the rice-duck-crayfish ternary ecological farming with the single and double rice systems, and found that the total nitrogen in the 0 cm~10 cm soil layer of the farming system was 8.5%~28.4% higher than the control, and the available nitrogen increased by 6.9%~22.7%. These data show that integrated farming can increase soil nitrogen reserves while maintaining a high level of available nitrogen. This is related to the provision of organic nitrogen by animal manure and the continuous release of nitrogen by microbial decomposition and mineralization. However, at different stages of the growing season, the dynamics of soil inorganic nitrogen will be jointly affected by plant absorption and loss processes. Some studies have observed that the ammonium nitrogen content in rice-duck fields is significantly higher than that in the control, while the difference in nitrate nitrogen is not obvious, indicating that the activity of ducks increases the circulation of ammonia but has little effect on nitrification. In terms of phosphorus, integrated farming introduces phosphorus into the soil through feed and biological cycles. Both total phosphorus and available phosphorus in rice-fish co-cultivation fields have increased. Gao et al. (2025) pointed out that the rice-duck model significantly enhanced the size of the soil available phosphorus pool and improved the effectiveness and utilization of phosphorus. This is related to the fact that duck manure contains more phytic phosphorus, which is converted into a form that can be absorbed by crops after microbial action. In the rice-fish-duck ternary co-cultivation system, the available phosphorus in the soil increased by 9%~16% compared with monoculture, indicating that the synergistic effect of multiple animals has an enrichment effect on soil phosphorus. Potassium mainly comes from soil background and organic matter mineralization. Studies have reported that the available potassium content in the soil of rice-duck farming can be increased by 8% to 39% compared with the control. The reason is that on the one hand, animal feces and residues are rich in potassium, and on the other hand, the stirring of aquatic animals promotes the release of soil mineral potassium. Meng et al. (2021) compared the single-crop, rice-fish and rice-shrimp modes in rice fields. The results showed that the available potassium in the soil of all integrated farming treatments was higher than that of the single-crop control. It should be noted that under different farming densities and management conditions, soil nutrients may also be locally excessive. For example, in rice-fish fields with large feeding amounts, the accumulation of soil phosphorus may cause surplus,
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