Molecular Soil Biology 2025, Vol.16, No.5, 272-286 http://bioscipublisher.com/index.php/msb 277 the topsoil, but also improved the stability of soil aggregates. The economic benefits of the rotation system have obvious advantages over single planting. The biological nitrogen fixation function of green manure crops (such as sweet potato and astragalus) can provide part of the nitrogen for the next legume crop, and its large amount of organic residues can improve soil fertility after turning over and returning to the field. Studies have shown that the carbon and nitrogen release dynamics of different legume green manures after turning over are slightly different, but they can all decompose quickly in the soil and release nutrients for subsequent use. For example, planting green manure Astragalus in southern red soil can increase soybean production by about 10% in the next season, and the soil organic matter content is 0.2 percentage points higher than that of fields without green manure (Chalise et al., 2019). Returning straw to the field is also an important measure to increase soil organic matter. The promotion of crushing corn straw and returning it to the field to plant soybeans in Northeast China can add a large amount of organic carbon source to the soil every year, which will form humus and improve soil physical and chemical properties after microbial decomposition. Yao et al. (2020) reported that the use of a "legume green manure-corn-wheat" three-way rotation and returning green manure and corn straw to the field not only achieved an increase in soil organic matter input throughout the year, but also effectively improved soil nutrient balance and soybean yield. It can be seen that increasing soil organic matter through green manure planting and returning organic materials to the field is a long-term strategy to improve the productivity of legume crops on various soils. It is necessary to select appropriate green manure varieties and return methods according to regional conditions. For example, annual leguminous green manure is suitable for use in the north, and Chinese milk vetch is often planted in winter in the double-season rice areas in the south to achieve soil fertility improvement and nutrient circulation. 4.3 Soil conditioners and pH adjustment technology For soil acidity and salinity problems, soil conditioners can be applied to adjust them. For acidic soils, lime (calcium carbonate or calcium oxide) is the most commonly used conditioner, which increases the pH value by neutralizing the active acid in the soil. Generally, applying 1~2 tons of lime per hectare can increase the pH of red soil from about 5.0 to above 6.0, and the number of nodules, plant height and biomass of soybeans on the improved soil are significantly increased (Li et al., 2021). In addition to lime, alkaline phosphate fertilizers containing calcium and magnesium (such as calcium magnesium phosphate fertilizers) can also partially neutralize soil acidity and supplement phosphorus, which is suitable for the fertilization plan of leguminous crops in acidic soils. For saline-alkali soils, the application of chemical gypsum (calcium sulfate) is an effective measure to control alkali damage. Ca²+ in gypsum can replace Na+ adsorbed on soil colloids, generating soluble Na2SO4 to be leached, thereby reducing the exchangeable sodium percentage of the soil and improving soil structure and permeability. Studies have shown that applying 2.5 tons of gypsum per hectare on sodic alkaline soil can significantly reduce soil conductivity and pH, and significantly increase soybean emergence rate and pod number (Yakuwa et al., 2022). New soil conditioners such as biochar and polymer water retainers are also beginning to be used in bean cultivation. Biochar has porosity and alkaline buffering capacity. Applying an appropriate amount of biochar to acidified soil can increase pH and provide a stable organic carbon source. A study applied biochar when planting peanuts in southern red soil and found that the soil pH increased by 0.5 units and the peanut yield increased by 9.8%. Water retainers can improve soil moisture retention capacity in sandy soils and reduce drought stress, which has a certain effect on improving the growth environment of drought-resistant legume crops such as mung beans. It should be noted that the use of amendments should be based on the soil test results to determine the reasonable dosage and frequency. Excessive application may cause secondary problems. For example, too much lime will lead to the fixation of trace elements and the decrease of biological activity, which requires supplementary organic fertilizer regulation. Soil amendments and pH adjustment technology are important measures to make up for the natural deficiencies of the soil and create an environment suitable for the growth of legumes. They should be scientifically implemented in combination with local soil types and crop needs. New technologies in recent years, such as bacterial agent regulation, have also shown potential. For example, some saprophytic fungal preparations can secrete organic acids to lower the pH of saline-alkali soils and promote the absorption of phosphorus by legume roots (Wen et al., 2024). Research in this area should be strengthened in the future to expand the technical means of soil improvement.
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