Legume Genomics and Genetics 2025, Vol.16, No.6, 253-269 http://cropscipublisher.com/index.php/lgg 258 the late reproductive stage. It should be noted that topdressing too late (such as in the late grain filling stage) is of little significance, because the leaf function declines when approaching maturity, and fertilization is difficult to convert into yield. Fertilization of beans should follow the timing strategy of "light in the front, control in the middle, and supplement in the back": less nitrogen and heavy phosphorus and potassium in the early growth stage, appropriate regulation in the middle stage depending on the growth, and necessary nutrients in the middle and late reproductive stages to maintain a higher functional leaf area and accumulation of assimilated products in the group, thereby achieving high yield. 3.3 Improvement of nutrient utilization efficiency under the synergistic effect of organic-inorganic fertilizers Long-term practice has proved that the combined application of chemical fertilizers and organic fertilizers (i.e., "organic-inorganic combination") is an important measure to balance crop high yield and soil fertility. This strategy is particularly applicable to legume crops, because organic fertilizers not only provide nutrients, but also improve the physical and chemical properties of the soil, promote the growth of rhizobia, and create a good environment for nitrogen fixation. Li et al. (2024) compared the effects of single chemical fertilizer application and organic-inorganic combination on soybean yield and quality in a long-term positioning experiment in Heilongjiang. The results showed that all fertilization treatments significantly increased yield by 5.1%-18.6% compared with no fertilization, among which the treatment with nitrogen, phosphorus and potassium chemical fertilizers combined with organic fertilizers had the best yield increase effect. The addition of organic fertilizers not only increased yield, but also significantly increased the nutritional content of protein, calcium and iron in soybean grains. Soil analysis shows that organic-inorganic combination can improve soil aggregate structure, increase soil organic matter and quick-acting nutrient content, thereby improving soil fertilizer supply capacity and fertilizer utilization efficiency. Another soybean field trial conducted in a semi-arid area further demonstrated the significant benefits of organic material application: under the same nutrient input, the soybean yield of chemical fertilizer + organic fertilizer + biofertilizer treatment increased by 28%-79% compared with the treatment of chemical fertilizer alone, and the water use efficiency was also improved simultaneously (Liu et al., 2024). This is attributed to the fact that organic fertilizer improves the soil water and fertilizer retention performance and root growth environment, allowing soybean plants to form a larger and deeper root system (root length and root surface area increased significantly), thereby absorbing water and nutrients more efficiently. Organic fertilizer can also buffer soil pH, provide crop trace elements, activate nutrients such as phosphorus fixed in the soil, and reduce fertilizer nutrient leaching and fixation. For legumes, since nitrogen fixation can partially replace chemical nitrogen fertilizers, using organic fertilizers to provide a basic nitrogen source is particularly in line with their needs. On the one hand, it avoids the inhibition of nodules by applying high amounts of quick-acting nitrogen fertilizers, and on the other hand, the decomposition of organic matter continues to provide nutrients for the crop in the late stage. The application of organic-inorganic fertilizers achieves a win-win situation of improving soil fertility and increasing crop yields by combining "nurturing the land with nurturing crops". In production, appropriate organic fertilizer sources (such as farmyard manure, green manure, crop straw compost, etc.) should be selected according to specific conditions for application, and the replacement ratio should be reasonably determined. For example, 20%-30% of the nutrients can generally be provided by organic fertilizers, and the rest can be supplemented by chemical fertilizers, thereby reducing the use of chemical fertilizers and optimizing the input structure. It should be noted that organic fertilizers have low nutrient content and are released slowly. When applying, they should be decomposed in advance and applied early to coincide with the peak of crop fertilizer absorption. By scientifically implementing the organic-inorganic combined fertilization strategy, the nutrient utilization efficiency and yield level of legume crops can be effectively improved, and a virtuous cycle of the agricultural environment can be promoted.
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