Acidification characteristics of soil in the main sugarcane planting areas in Guangxi

【Objective】 The present situation and distribution characteristics of soil pH in the main sugarcane planting areas of Guangxi and the relationship between soil pH and exchangeable base cations contents and soil exchangeable aluminum content were analyzed，which provided scientific basis for exploring the mechanism of soil acidification and soil acidification control in sugarcane areas of Guangxi. 【Method】 In the spring of 2023，a total of 515 soil samples were collected from 15 counties（districts or cities）with large sugarcane planting areas in Guangxi. The soil pH was measured using deionized water，0.01 mol/L CaCl₂ solution and 1 mol/L KCl solution，denoted as pH（H₂O），pH（CaCl₂），and pH （KCl）respectively. Additionally，the contents of exchangeable base cations，exchangeable acids，and exchangeable aluminum were measured. The relationship between soil pH and exchangeable base cations and the relationship between soil pH and base saturation were analyzed，and the response of exchangeable aluminum accumulation to soil pH was also analyzed. 【Result】 The average soil pH（H₂O）in the main sugarcane planting areas of Guangxi was 4.52，and strongly acidic soil with pH（H₂O）<4.5 accounted for 63.9%. The average values of pH（CaCl₂）and pH（KCl）were 4.06 and 3.71 respectively，which were 0.46 and 0.81 lower compared to pH（H₂O）. The average content of soil exchangeable acid was 4.59 cmol/kg，and soil with exchangeable acid >6.0 cmol/kg accounted for 32.8%. In exchangeable acids，exchangeable aluminum was the dominant component. In soils with exchangeable acids content >4.0 cmol/kg，the proportion of exchangeable aluminum exceeded 80.0%. The equation fitted with pH（KCl）and soil exchangeable aluminum content had the highest goodness fit（R²=0.9005）. When the soil exchangeable aluminum content was 2.0 cmol/kg，the corresponding average values for pH（H₂O），pH（CaCl₂），and pH（KCl）were 4.67，4.07，and 3.66 respectively. The average contents of exchangeable calcium，exchangeable magnesium and exchangeable potassium in the soil were 4.67，0.42 and 0.49 cmol/kg respectively. Soil with exchangeable calcium content <1.5 cmol/kg accounted for 31.1%，soil with exchangeable magnesium content <0.25 cmol/kg accounted for 31.7%，and soil with exchangeable potassium content ranging from 0.2 to 0.6 cmol/kg was more commonly found，accounted for 46.8%. The average soil base saturation was 49.5%，and soil with base saturation below 20% accounted for 15.3%. Base saturation，and the contents of exchangeable calcium and exchangeable magnesium were all extremely significantly and positively correlated with soil pH（H₂O），pH（CaCl₂）and pH（KCl）（P<0.01）. 【Conclusion】 The main sugarcane planting areas in Guangxi is suffering from severe soil acidification，with most soils having a pH≤4.5. The lack of calcium and magnesium，low base saturation and high risk of aluminum toxicity have become the main characteristics of soil acidification in the main sugarcane planting areas in Guangxi.