Rice Genomics and Genetics 2025, Vol.16, No.2, 71-85 http://cropscipublisher.com/index.php/rgg 78 and resource utilization is relatively sufficient in the middle and late stages, but excessive density may cause fertilizer waste due to early aging in the later stage. Therefore, reasonable water and fertilizer management and density adjustment are required to be optimized simultaneously. 4.3 Influence on yield stability across seasons The optimal density will vary in different ecological regions and varieties. For example, in the northern single-season rice areas with sufficient light temperature, individual production potential is great, and lower density is often used to give full play to the advantages of large ears. In the southern double-season rice areas, the density is relatively high due to the short growth period and the emphasis on population ears. Jiang et al. (2017) found in the experiments of the middle and lower reaches of the Yangtze River that compared with plain areas, dense planting in hilly areas (poor ecological conditions) has a more obvious effect on the increase in yield, and a higher basic seedling is needed to ensure sufficient ear count. On the contrary, in areas with high soil fertility and sufficient light, slightly thinning is conducive to cultivating large ears and achieving the combination of "large ears and many ears". In terms of variety, conventional rice or japonica rice with strong tillering ability can generally have a lower density to allow them to fully tiller; hybrid indica rice with weak tillering ability needs to rely on higher basic seedlings to make up for the ear number. For example, the optimal basic seedling density for conventional japonica rice is about 30 plants/m2, while the maximum yield for hybrid two-line rice is about 12 plants/m2 (Hu et al., 2025). This reflects the importance of adjusting density according to variety characteristics. At the yield and constituent factors, the optimization of planting density mainly revolves around the balance between increasing the number of ears and maintaining appropriate ear types. A large number of experimental data support the law of "medium density and high yield", that is, extreme sparse planting or extreme dense planting is not conducive to the maximum output. In practice, a reasonable basic seedling range should be determined based on local ecological conditions and variety characteristics. On this basis, fertilizer and water management are supplemented to achieve the best matching of group production and resource utilization, and obtain high yields, stable yields and good rice quality. Both research and practical experience show that optimizing planting density is a simple and efficient high-yield cultivation method, which is of great significance to improving quality and efficiency of modern rice production. 5 Economic Benefit Evaluation In the optimization of agronomic measures, we should not only pay attention to the increase in yield itself, but also evaluate the changes in input-output and economic benefits. The impact of optimizing planting density on the economic benefits of rice production is mainly reflected through the combined effects of yield benefits, seed costs, fertilizer and pesticide inputs, and risk factors. 5.1 Net return per hectare From the perspective of yield benefits, the above analysis shows that reasonable dense planting can increase yield per unit area, thereby directly increasing grain output benefits. When other inputs remain unchanged, yield increase means increased sales revenue. For example, Tang et al. (2020) reported that the per mu yield of high-quality late rice increased by about 5% under density optimization treatment. According to the market rice price, the increase in income per mu was about 100 yuan (assuming rice is 2.5 yuan/kg), showing positive economic benefits. However, it is necessary to consider that excessive density may lead to a decline in rice quality or a decrease in the selling price. If the rice quality declines significantly, it may partially offset the benefits brought by the increase in yield. Therefore, in the production of high-quality rice, density adjustment should take into account both yield and quality to ensure an increase in total benefits. 5.2 Cost-benefit comparison under different densities Seed and cultivation costs change with density. Increasing the planting density usually means an increase in the amount of sowing or the number of seedlings, and an increase in seed costs. However, in areas with a high degree of mechanization, the proportion of seed costs in the total cost is not large. For example, if the sowing amount per mu increases by 1 kg, the cost will only increase by about 20 yuan, which is still a cost-effective investment
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