中国酸性土壤利用的科学问题与策略

中国土壤酸化呈现出全国普遍发生的趋势，对作物产量、农产品品质和生物多样性造成不利影响。自20世纪50年代以来，我国在酸性土壤方面开展了大量工作，取得显著成效，但因我国酸性土壤分布详情不明、土壤酸化机制存在争议、耐逆作物品种缺乏、作物酸害阈值不清、改良产品及技术落地性差等问题，酸性土壤利用仍受到极大限制。针对上述问题，绘制了新的中国土壤酸碱度图，明确了我国酸性土壤的分布详情，讨论了土壤酸化机制特别是氮肥与土壤酸化之间的关系，论述了土壤酸化的危害，解析了植物和微生物对酸性土壤的响应和适应机制，提出了分区分级分类改良、酸度改良和肥力提高并重、有机无机肥配施、发展特色农业等酸性土壤改良和利用策略，建议进一步加强酸性土壤新型改良剂、作物酸害阈值、氮肥高效利用、中微量元素、耐逆作物育种和土壤酸化模型等方面研究，以期为酸性土壤可持续利用提供支撑。

Scientific Issues and Strategies of Acid Soil Use in China

Most soils in China have acidified to some degree in the past decades. This increase in soil acidity has a negative impact on crop yield, agricultural product quality, and biodiversity. Since the 1950s, Chinese scientists have performed lots of work on acid soils and the achievements are significant. However, there are still some issues in the use of acid soils including the inexact distribution of acid soils in China, controversial explanation for soil acidification mechanisms in cropland, lack of acid soil-tolerant crop cultivars, unclear critical pH for optimal plant growth, and poor applicability of products and techniques in acid soils, which limits acid soil use. Considering these issues, a new soil pH map of China based on the recently obtained soil data was drew. The area of acid soils with pH values lower than pH 6.5 is about 3.11 million km2, accounting for 32.4% of the total national land area. About 60.3%, 23.3%, and 16.4% of these acid soils are distributed in the south red and yellow soil region, northeast region, and other regions in China, respectively. The mechanisms for soil acidification under natural conditions and by acid deposition are much clearer, but whether nitrogen fertilizer induces cropland soil acidification is controversial. The relationship between soil acidification and nitrogen fertilizer is very complicated, depending on the production and consumption of H+ during soil nitrogen transformation. Large amounts of nitrate loss through leaching may be the main mechanism for soil acidification induced by nitrogen fertilizer, so it is suggested that the inhibition of soil nitrification can be used as an effective measure to alleviate soil acidification, especially in south acid soil regions of China with dual effects of high nitrogen use efficiency and low nitrogen loss. Soil acidification has various negative effects, including inhibition of plant growth, reduction of agricultural product quality, and damage to ecological environments. Nitrogen fertilizer induced serious soil acidification and remarkably decreased crop yield in some red soil regions of south China. In addition, increased soil heavy metal bioavailability, pests, and diseases by soil acidification have become important issues in recent years. Plants and microbes have developed external and internal mechanisms to tolerate various stressful factors such as aluminum toxicity, phosphorus deficiency, and manganese toxicity co-existing in acid soils. Nevertheless, how to apply these mechanisms to the improvement of crop productivity in acid soils remains a huge challenge. Four strategies are proposed for the improvement and use of acid soils: (1) the improvement strategies for acid soils should be implemented according to soil requirements in different districts, acidity grades, and soil types; (2) the same importance for improving soil acidity and fertility should be accorded to all acid soils; (3) the combined application of organic and chemical fertilizers should be encouraged; and (4) the development of agriculture with local acid soil characteristics should be the new focus. Furthermore, six research directions to be strengthened in the future are suggested: (1) develop new products for the improvement of acid soils; (2) clarify the critical pH for optimal growth of different crops; (3) research efficient N application techniques for reducing soil acidification; (4) emphasize the role of micro-elements in plants in acid soils; (5) breed acid soil-tolerant crop cultivars; and (6) predict soil acidification trend in the following period. Provided the national soil acidification trend, the Chinese government has begun to stop soil acidification in 20 counties of 15 provinces since 2023. At the same time, several national projects related to acid soils are being performed and/or will be approved. With the implementation of these projects, soil acidification in China will be effectively controlled, and the quality and productivity of acid soils will be greatly improved. This will lay a solid foundation for ensuring food security.