Legume Genomics and Genetics 2025, Vol.16, No.6, 253-269 http://cropscipublisher.com/index.php/lgg 264 From a national perspective, China's fertilizer utilization rate is low at only 30%-40%, and nearly half of the fertilizer nutrients are lost and wasted. By balancing fertilization and improving fertilizer varieties (such as controlled-release fertilizers and biofertilizers), fertilizer utilization efficiency is expected to increase to more than 50%, thereby reducing the amount of fertilizer used at the same yield or increasing yield at the same amount (Zhou et al., 2019; Pierozan et al., 2023). Economically, this means a reduction in the cost of fertilizer per kilogram of grain. Taking controlled-release fertilizers as an example, although their price is higher than that of ordinary fertilizers, because of the reduction of loss and multiple applications, crops actually get more nutrients, the fertilizer effect period is extended, and the unit nutrient output rate is improved. For example, in the Qiqihar experiment, the nitrogen input of the controlled-release fertilizer treatment was the same as that of the conventional treatment, but the nitrogen fertilizer recovery rate (the proportion of nitrogen absorbed by the plant to the amount of nitrogen applied) increased by about 10 percentage points, which is equivalent to producing more products without increasing input. Agricultural producers usually value the input-output ratio, and through optimized management, "one input, multiple outputs" can be achieved. Density planting and fertilization optimization may also bring some hidden benefits. For example, nitrogen reduction can reduce energy consumption and carbon emissions caused by nitrogen fertilizer production and application, which is beneficial to long-term environmental and economic benefits. Of course, in specific applications, attention should be paid to the marginal balance between input and benefit. For example, blindly too high density may lead to increased diseases and reduced quality, thereby offsetting economic benefits. Therefore, it should be stopped when the output and benefit peaks are reached. Similarly, the more fertilizer input, the better. It should be based on achieving efficient utilization. Increasing input blindly will only reduce input-output efficiency. By measuring the cost-effectiveness of different technical combinations, farmers can be provided with a basis for decision-making: such as whether it is cost-effective to use more expensive new fertilizers, and whether the additional management brought by increased density is worthwhile. Optimized management improves resource utilization and output efficiency, and has significant economic rationality. Especially in the context of rising fertilizer prices and stricter environmental regulations, measures to reduce fertilizer and increase efficiency can reduce planting costs, increase profits and reduce environmental costs, which can be described as a win-win move. 6.2 The impact of dense planting on the incidence of diseases and prevention and control suggestions Dense planting is a "double-edged sword". While increasing production, it may also change the field microclimate, thereby affecting the occurrence and development of pests and diseases. Generally, dense planting will lead to a reduction in plant spacing, poor ventilation and light transmission, and field humidity and temperature that are more suitable for the spread of certain diseases such as fungal diseases. For example, soybean powdery mildew and sclerotinia are more likely to break out in a closed and humid environment, and the occurrence of white mold (sclerotinia) often increases with the increase in planting density. However, not all diseases increase under dense planting conditions. Some root diseases caused by soil-borne pathogens may be reduced due to shading and cooling of the soil by dense planting. The key is that dense planting changes the environmental factors and host resistance in the disease triangle (host-pathogen-environment). In order to minimize the disease losses that may be caused by dense planting, the following prevention and control strategies can be adopted: select disease-resistant and dense-tolerant varieties to reduce the possibility of disease occurrence from the variety. For example, densely planted varieties tend to have upright plant shapes, narrow leaves, good ventilation at the bottom, and stronger resistance to gray spot diseases. Optimize the cultivation layout, such as reasonable row spacing and strip planting, so that the field can reach the target density while retaining certain ventilation channels (Potratz et al., 2019). Implement enhanced disease monitoring and prevention in densely planted fields. For example, pay close attention to the source of sclerotinia disease before and after the flowering period of soybeans, and spray protective fungicides in advance if necessary (Yang et al., 2022). Spraying carbendazim at the beginning of flowering to prevent sclerotinia disease has good results, and no large-scale disease outbreaks have occurred during the entire growth period. Plants treated with sufficient
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