Legume Genomics and Genetics 2025, Vol.16, No.6, 279-287 http://cropscipublisher.com/index.php/lgg 283 increase biomass and grain yield per mu when the density is high, but the increase is different. For example, if the density of the determinate "Wuyin No. 9" is doubled, its yield can be increased by 93%; the semi-determinate "You 91-19" only increases by 37%, and the indeterminate "Jufeng" increases by 43%. However, under high density, the biomass and grain weight of the determinate plant are not greatly affected, while the weight of the late-maturing indeterminate plant drops sharply (Stulen et al., 2002). This shows that choosing the right genotype is critical to getting high yields at a specific density. 6.2 Genetic traits associated with high-density adaptability Varieties that can produce stable yields at high density usually have some special physiological and morphological characteristics. Their leaf area ratio (LAR) and specific leaf area (SLA) tend to remain stable or even higher, and their nitrogen fixation efficiency is also good. The yield of a limited-growth plant is less affected by crowding; because the unlimited-growth plant competes more fiercely for light and fertilizer, the biomass and grain weight of a single plant decrease more. These phenomena show that in order to make soybeans suitable for high density, we must rely on traits that can efficiently utilize resources and are less sensitive to crowding. 6.3 Breeding considerations for density-tolerant varieties When breeding density-tolerant soybeans, we should look for genotypes that can produce stable yields at different densities, especially those with limited or semi-limited growth, because they do not drop much per plant yield under crowded conditions. We should focus on several physiological indicators: appropriate LAR, SLA, and strong N₂ fixation ability. If these characteristics are integrated into the breeding program, new varieties that do not sacrifice seed quality and have strong plants at high density can be cultivated, so that soybean cultivation can continue to develop in an intensive and sustainable direction. 7 Case Study: Application in China 7.1 Background: local climate, soil type, and soybean farming practices The main soybean growing areas in China are Northeast China and Southern Xinjiang, where the climate and soil conditions are quite different. Northeast China has fertile black soil and a relatively mild climate, making it one of the most important soybean growing areas in my country (Guo et al., 2022b). In Southern Xinjiang, the growing season is short, and soybeans and winter wheat are often planted in rotation, which requires more careful arrangement of sowing time and density to get a good yield. At present, the planting methods in many places are still determined by farmers' experience, not relying on data analysis, which makes the sowing density and input level vary significantly in different places. 7.2 Trial results of different sowing densities on local soybean cultivars In the Northeast, Heihe No. 43 was used as the test material. The test found that on the basis of applying a certain amount of fertilizer, the yield was the highest when 45.37×10⁴ plants/hectare were planted, reaching 3816.67 kg/hectare. In East China, five varieties participated in the test and found that as the density increased, the yield also increased, but when the density exceeded 160,000-180,000 plants/hectare (the specific figures vary slightly depending on the variety), the yield declined due to fierce competition (Han et al., 2021). In southern Xinjiang, the test results showed that early sowing with low density (for example, 206,800 plants/hectare) can achieve the best results, with the highest yield and a more reasonable canopy structure; while late sowing with high density, the plants grow tall and thin, and the yield is reduced (Figure 2). These experiments show that the sowing density must be matched with the local variety characteristics and environmental conditions, and cannot be a one-size-fits-all approach. 7.3 Lessons learned and recommendations for scalable implementation The optimal density for each place and variety is different. If you want to get high yields, you have to give localized suggestions based on local conditions (Huang et al., 2024). If the appropriate density can be matched with the amount of fertilizer and sowing time, the yield will be significantly improved, and the yield difference between regions can be narrowed (Wang et al., 2023). The current management method should gradually shift from "relying on experience" to "relying on data", and more accurate planting suggestions can be obtained
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