In recent years, as the duration and area of teagarden cultivation have increased, soil acidification in teagardens has become a hot topic in soil environmental quality research. The suitable pH range for Tea plant growth is 4.0 to 6.5. A pH that is too low can inhibit the growth and Metabolism of tea plants, affect soil fertility, reduce tea yield and quality, and severely threaten the natural ecological environment and sustainable development of teagardens. This issue will follow up on the previous content by summarizing the remediation measures for soil acidification in Chinese teagardens and outlining future research directions for soil acidification in teagardens.
1 Chemical Improvement
Generally speaking, when the soil pH value is less than 4, it is advisable to consider chemical measures for soil improvement. Traditional agricultural practices usually involve applying lime or other alkaline materials to improve the acidic properties of farmland soils. However, the methods and precautions for using lime are relatively complex, and improper application can have negative effects on teagarden yields and soil quality. Currently, dolomite powder is more commonly used to increase soil pH. Dolomite powder, mainly composed of calcium carbonate and magnesium carbonate, reacts chemically with acidic ions after being applied to the soil, consuming acidic substances and raising the soil pH. Additionally, the abundant calcium and magnesium ions can increase the cation exchange capacity of the soil and significantly reduce the content of exchangeable aluminum in the soil. When dolomite powder is applied at rates greater than 1500 kg/hm², the problem of soil acidification in teagardens is considerably improved. Adding Spanish river carbonates to field and pot experiments with tea plants can also result in a significant increase in soil pH. Therefore, dolomite powder is easier to use and more effective compared to lime.
2 Biological Improvement
Biochar is a charred product obtained from the pyrolysis of biomass under anaerobic and high-temperature conditions. Studies have shown that biochar, as a special soil conditioner, contains many oxygen-containing functional groups on its surface and is mostly alkaline. It can improve the acidity and alkalinity of farmland soils, increase cation exchange capacity, reduce the content of exchangeable acids, and enhance the soil's ability to retain water and nutrients. Furthermore, biochar contains rich mineral elements that can promote nutrient cycling in the soil and the growth and development of plants, altering the structure of soil microbial communities. Applying 30 t/hm² of black biochar can significantly improve the acidified environment of teagarden soils. Studies on applying different types of biochar to teagardens have found that the extent of pH increase is related to the type of biochar and positively correlated with the amount applied.
Green manure, made from green plants, is green and non-toxic, and has a good effect on improving soil properties. After green manure reaches a certain stage of growth, it is harvested and plowed into the soil, where it decomposes through biological metabolic processes, improving soil properties. Planting green manure in acidic teagarden soils not only improves soil acidification but also alters soil physical structure, achieving the effects of increasing tea yield and quality.
Compared to other measures, biological improvement is healthier, more environmentally friendly, and produces milder effects, making it one of the effective measures for improving acidic soil properties. 3 Organic Improvement
Organic fertilizers are processed from organic matter, eliminating harmful substances while retaining various beneficial substances. For acidified soil improvement, neutral or slightly alkaline organic fertilizers can be used to correct the acidic soil environment, providing a variety of nutrients while maintaining long-term slow-release fertility.
However, the nutrients in organic fertilizers are difficult for plants to directly utilize. After the growth and metabolism of microorganisms, they can slowly release plant-absorbable organic matter, thereby improving the physical and chemical properties of the soil. Applying a composite acidification improver of organic and inorganic materials to acidic soils in teagardens can effectively raise the soil pH and increase soil fertility, supplementing various base ions to enhance soil buffering capacity. By applying different proportions of biologically-based substrate fertilizers to teagardens, it was found that applying fermented bedding from pig farms improved the degree of soil pH acidification in teagardens, and the total amount of soil base ions increased, with the improvement effect increasing as the proportion of organic fertilizer applied increased. However, there are significant differences in the physicochemical properties of different types of organic fertilizers, and ordinary processing methods (such as farmer composting) need to confirm whether heavy metal elements exceed standards. If they do not exceed standards, appropriate additions can be made based on soil properties.
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New Improvement Methods
New remediation materials are beginning to emerge in soil remediation and improvement. Microorganisms play an important role in soil nutrient cycling and can influence soil physical and chemical properties. Applying microbial inoculants to teagarden soils can increase soil microbial activity, enhance the abundance of soil microbes, and significantly improve various fertility indicators. Bacillus amyloliquifaciens can improve tea quality and yield, with the best results when the bacterial count is 1.6 × 10^8 cfu/mL. Continuous application of microbial inoculants (mainly Bacillus and Trichoderma) can increase the abundance of soil microbes, and their metabolites can improve soil fertility and effectively control soil acidification in teagardens. However, the mechanisms of microbial improvement of acidic soils in teagarden root zones are not yet clear enough, and future research could delve deeper into this direction.
Polymers are also effective new soil property improvers. Large molecular polymers can increase the number of large soil aggregates, improve porosity, and improve soil structure. Applying polyacrylamide to acidic soils can moderately raise soil pH and regulate soil properties well. Treating latosols with humic acid copolymerized with other materials can improve soil properties and slightly increase pH. However, these materials have not been tested in acidified teagarden soils, and studies on improving other acidic soils have only conducted pot trials indoors without field trials. Currently, there is little research on the effects of polymers on acidified soils in teagardens, leaving considerable room for exploration. Combining new improvers with traditional measures to improve soil acidification in teagardens may become a future research hotspot.
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Rational Fertilization
The excessive and improper use of chemical fertilizers is one of the main reasons for soil acidification. Chemical fertilizers can quickly change the nutrient content of teagarden soils. For example, imbalanced fertilization can lead to imbalances in soil nutrients, easily exacerbating soil reaction conditions. In particular, long-term application of acidic fertilizers, physiologically acidic fertilizers, or nitrogen fertilizers alone can cause soil acidification. Therefore, teagardens should not emphasize the exclusive use of nitrogen fertilizers but should pay attention to the combined application of nitrogen, phosphorus, potassium, and other elements. To balance soil nutrients and prevent soil acidification, it is advisable to apply fertilizers according to their absorption characteristics and soil properties, using soil testing and formula fertilization or mixing and applying multiple fertilizers after compound blending. Tea farmers need to fully recognize the foundational role of soil health and safety in the sustainable development of the tea industry. They should use various venues to publicize the importance of tea quality safety, firmly establish a sense of crisis and responsibility, and take the protection of a good ecological teagarden environment, scientific and rational fertilization, and achieving soil nutrient balance as the foundation for the sustainable development of the tea industry.
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Outlook
In the future, efforts should focus on strengthening the management of the root causes leading to soil acidification and continue to pay attention to research on methods for restoring acidic soils