Abstract:
                                      Soil acidification has become a significant factor constraining the sustainable development of agriculture and ecological safety. The dual challenges of soil acidity and fluoride contamination commonly coexist in the acidic soils of southern China. Although amendments applied to remediate soil acidity and those used to mitigate fluoride contamination share similarities, few amendments are highly effective at simultaneously addressing both issues. Therefore, in this study, we aimed to evaluate and identify effective inorganic amendments capable of concurrently remediating acidity and fluoride contamination in acidic soils. Eleven representative inorganic amendments — including minerals, industrial by-products, and commercial materials rich in calcium and magnesium — were selected for this study. Their effectiveness was investigated through indoor incubation experiments for assessing their capacity to neutralize soil acidity, reduce soluble fluoride levels, and enhance soil nutrient availability. The soil quality index (SQI) was employed as a quantitative parameter to evaluate each amendment’s comprehensive efficiency in decreasing soil acidity and soluble fluoride levels, while increasing mineral nutrient content. The results indicated that these inorganic amendments could reduce soil acidity to varying degrees, and their ameliorative effects were primarily determined by their acid-neutralizing capacity. Notably, the pH of the amendments, which serves as an indicator of their acidity or alkalinity, did not accurately reflect their acid-neutralizing capacity. The primary components contributing to the neutralization of soil acidity included carbonates such as calcite and dolomite, as well as easily dissolved silicates and phosphate minerals. These amendments not only increased soil pH but also significantly reduced the contents of soluble aluminum, exchangeable aluminum, and soluble fluoride. Additionally, using a 0.01 mol∙L
−1 CaCl
2 solution to measure soil pH eliminated ionic strength effects, offering a more accurate reflection of the actual effectiveness of amendments in alleviating soil acidity. The effectiveness of inorganic amendments in mitigating fluoride contamination depended on their ability to increase soil pH and was further influenced by their soluble salt content. Elevating the soil pH to neutral facilitated the coprecipitation of soluble fluoride with calcium or magnesium ions supplied by the amendments, thereby effectively reducing fluoride availability. Nevertheless, amendments with soluble sulfates and chlorides — particularly those containing fluoride — were not effective in decreasing soluble fluoride contents and may promote the formation of soluble aluminum-fluoride complexes, thereby intensifying the environmental risk of aluminum toxicity. Furthermore, all amendments increased the availability of soil mineral nutrients such as potassium, calcium, magnesium, and phosphorus to different degrees, and these nutrient increments were dependent on the corresponding nutrient content in the amendments. A comprehensive evaluation based on SQI values revealed that limestone, weathered coal, wollastonite, silicon-calcium-magnesium conditioners, and dolomite were particularly effective in remediating fluoride-contaminated acidic soils. Conversely, attapulgite, biomass ash, alkali slag, and the commonly used calcium-magnesium-phosphate fertilizer were unsuitable for remediation purposes in such soils. The findings of this study provide valuable technical guidance for the effective management of multiple constraints — including acidity, aluminum toxicity, and fluoride contamination — in acidic soils, thereby promoting soil quality restoration and sustainable agricultural development.