Molecular Soil Biology 2025, Vol.16, No.5, 272-286 http://bioscipublisher.com/index.php/msb 278 5 Optimization of Fertilization and Inoculation Strategies 5.1 Soil type and fertilizer formula adjustment principles Reasonable adjustment of fertilizer formula and dosage according to soil type is the key to the nutritional management of legume crops. Fertilizer management should take into account the fertilizer supply capacity and limiting nutrients of different soils. For example, for loam and black soil with high organic matter content, the amount of nitrogen fertilizer can be appropriately reduced, and more nitrogen can be provided by soil mineralization and leguminous nitrogen fixation to avoid excessive nitrogen inhibiting nitrogen fixation (Ciampitti et al., 2021). On the contrary, on poor sandy soil or red soil, it is necessary to increase the input of nitrogen, phosphorus and potassium in basal fertilizer and topdressing accordingly, and adopt the principle of small amounts and multiple times to prevent nutrient leaching. Generally speaking, clay has good fertilizer retention but often lacks effective phosphorus, and the proportion of water-soluble phosphorus should be increased in the phosphate fertilizer formula; sandy soil is prone to potassium deficiency, and the proportion of potassium and organic fertilizer in fertilizer should be increased. Soil testing and formula fertilization can adjust the fertilizer composition according to the nutrient abundance and deficiency conditions of different soils. For example, the effective iron and zinc in the alkaline soil of Huanghuaihai is low, so special compound fertilizers containing trace elements or foliar spraying of micro-fertilizers should be added to soybeans to prevent symptoms such as iron deficiency and chlorosis. Long-term positioning experiments have shown that balanced application of nitrogen, phosphorus and potassium in black soil combined with organic fertilizers can maintain stable soil fertility while ensuring yield (Zhang et al., 2021). The study by Ren et al. (2022) further pointed out that on loam with medium fertility, the best fertilization mode for high soybean yield is "organic fertilizer + appropriate fertilizer", in which organic sources of nitrogen account for 50%, and combined with a high planting density, high yield and high efficiency can be achieved. This result is of reference significance for similar soil types. In short, the principle of fertilization is: fertilizer input matches the soil fertility and adapts to crop needs, avoiding excessive fertilization waste due to high soil fertility and preventing insufficient nutrient input and reduced yield when the soil is barren. For some special soils, such as calcareous soils, acidic or neutral fertilizers can be used in combination with sulfur fertilizers and micro-fertilizers to improve nutrient utilization. For example, in red soil areas, attention should be paid to the combination of phosphorus and potassium fertilizers and organic fertilizers to improve soil acidity while providing a slow-release nutrient source. Through the above soil-based fertilization strategy, the soil's own potential and the benefits of exogenous nutrients can be maximized, and efficient coordination of nutrient management of legume crops can be achieved. 5.2 Inoculation effect of microbial preparations such as rhizobia and phosphorus bacteria The application of microbial fertilizers (microbial preparations) is one of the effective measures to improve the nutrient utilization and adaptability of legume crops to adversity. For legume crops, inoculation of high-efficiency rhizobia has almost become a standard practice in the field of soybeans, peanuts, etc. The inoculation of excellent strains can significantly increase the number of nodules and increase the activity of nitrogenase, thereby providing more nitrogen nutrients for bean plants (Zhang et al., 2024). For example, Ma et al. (2020) reported that after inoculating suitable soybean rhizobia in acidic soils in the southwest, the photosynthetic rate and nitrogen fixation ability of soybeans were improved, and the final pod yield was more than 10% higher than that of the uninoculated control. In addition to rhizobia, functional bacterial agents such as phosphorus bacteria and nitrogen-fixing bacteria that have been promoted in recent years have also shown good results in bean cultivation. Phosphorus bacteria can dissolve insoluble phosphates in the soil and increase the absorption rate of phosphorus by legumes; autogenic nitrogen-fixing bacteria can provide additional nitrogen sources for crops in the rhizosphere. Field experiments have shown that inoculating phosphate-solubilizing bacteria on phosphorus-deficient red soil can increase the phosphorus accumulation of peanut plants by 15%, and inoculating nitrogen-fixing bacteria and rhizobia on saline-alkali soil can increase the number of soybean nodules and improve salt tolerance (de Almeida et al., 2022). However, it should be noted that the actual effect of microbial preparations is closely related to soil type and background microbial flora. Zhang et al. (2024) found that in two soils in the Huaihe River Basin of Anhui Province, inoculation with the same rhizobia resulted in completely different results: inoculation in the slightly acidic yellow-brown soil increased soybean nitrogen accumulation by
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