Molecular Soil Biology 2025, Vol.16, No.4, 214-229 http://bioscipublisher.com/index.php/msb 217 4.2 Chemical amendments Lime (also known as calcium carbonate) is mainly used to adjust the pH of the soil. It can reduce aluminum toxicity in the soil and make elements such as calcium and magnesium more easily absorbed, which is very helpful for crop growth and microbial activity (Bossolani et al., 2020; 2021; De Campos et al., 2022). Long-term use of lime can significantly improve soil quality and increase yields. Gypsum (calcium sulfate) is more suitable for use in saline-alkali land or heavy clay soils. It can replace sodium ions in the soil, improve soil structure, make water more easily infiltrated, and is also beneficial to the development of the root system (Bossolani et al., 2020; 2021). Organic fertilizers (such as compost and humus) are rich in organic matter and various nutrients, which can increase soil fertility, make soil better, make microorganisms more active, and increase crop yields (Doan et al., 2015; Lal, 2015; Tian et al., 2020; Liu et al., 2022; Yan et al., 2023; Zhang et al., 2023; Zhao et al., 2023). Biochar is a porous material that can absorb water and fertilizer, adjust pH, adsorb harmful substances, and provide a "home" for beneficial microorganisms. If used together with organic fertilizers, the effect is better (Doan et al., 2015; Liu et al., 2022; Yan et al., 2023; Deng et al., 2024; Kong et al., 2024). 4.3 Biological interventions Green manure, such as sweet potato and alfalfa, can be turned into the soil when they are almost grown, which can increase organic matter, supplement nitrogen, and improve soil structure. This method can reduce the use of chemical fertilizers, prevent nitrogen loss, and increase crop nitrogen absorption and yield (Liang et al., 2022; Khangura et al., 2023). Microbial fertilizers (such as rhizobia, phosphate-solubilizing bacteria, growth-promoting bacteria, etc.) can help nutrient conversion, improve crop adaptability to the environment, and regulate the micro-ecosystem in the soil, which is beneficial to yield and quality (Das et al., 2022; Deng et al., 2024; Lüet al., 2024; Wei et al., 2024). There are a lot of humus and beneficial bacteria in vermicompost, which can improve soil fertility, improve structure, enhance drought and disease resistance, and reduce nutrient loss (Doan et al., 2015; Ding et al., 2020). 4.4 Comparative summary table Physical methods such as deep plowing, mulching, sand mixing and high ridges are mainly to make the soil structure better, more aerated, and easier to retain water, which can help the root system grow better and increase crop yields. Chemical amendments, such as lime, gypsum, organic fertilizer and biochar, mainly regulate pH, supplement nutrients, and add organic matter, which can make the soil more fertile and the microorganisms more active. Biological intervention methods, such as green manure, microbial fertilizer and vermicompost, pay more attention to organic matter and nutrient cycles, and can improve the stability and sustainability of the soil ecosystem. Each method has its own advantages. When used in practice, it is best to use them in combination according to the actual situation of the soil and the needs of the crop. 5 Effects of Soil Improvement on Soil Properties 5.1 Changes in pH, porosity, water retention, and nutrient profiles After soil improvement, the physical and chemical properties of the soil will be significantly improved. Many studies have found that adding materials such as organic fertilizers, humus, straw, lime, gypsum, biochar, or zeolite can adjust the pH of the soil, increase porosity, make the soil more water-retaining, and improve nutrient levels. Biochar and organic fertilizers can increase or decrease the pH of the soil, depending on whether the original soil is acidic or not and the type of amendment. When biochar is added to acidic soil, the pH will increase; while the use of acidified biochar in alkaline soil can neutralize the alkalinity problem (Blanco-Canqui, 2017; Singh et al., 2022; Guan et al., 2024). As for the porosity and water retention of the soil, adding biochar, straw or sand can significantly improve the air permeability of the soil, increase the porosity by 8.3% to 64%, and increase the water retention by 2.2% to 130%, while the soil becomes less compact (Blanco-Canqui, 2017; De Jesus Duarte et al., 2019; Kok et al., 2023; Li et al., 2025). The long-term use of organic fertilizers and compost can also make the soil more granular and more water-retaining (Aggelides and Londra, 2000; Bhogal et al., 2018; Dhaliwal et al., 2019; Fu et al., 2022). In terms of nutrients, amendments can increase the content of organic matter, total nitrogen, available phosphorus and available potassium, sometimes even by 20% to 100%. At the same time, it can also
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