Distribution Characteristics and Relationships of Soil pH, Exchangeable Ca²⁺, Mg²⁺ and CaCO₃ in Tobacco-planting Fields in Guizhou

  Objective  This study aims to understand the distribution characteristics and the relationships among soil pH, Ca²⁺, Mg²⁺ and CaCO₃ in tobacco-planting fields in Guizhou and then scientifically to guide the adjustment of soil acidity or alkalinity as well as the application of calcium and magnesium fertilizers.

  Method  Topsoil samples (0-20 cm) were collected from 500 typical tobacco-planting fields widely distributed in Guizhou. Soil pH, exchangeable Ca²⁺, Mg²⁺ and CaCO₃ were determined, and then the content changes and correlation regression models among different parent materials, soil types and regions were analyzed and discussed with SPSS.

  Result  According to the suitability for tobacco-planting, 20.0%, 18.2% and 56.4% of samples were lower and 37.0%, 55.8% and 29.6% were higher in pH values, Ca²⁺ and Mg²⁺ contents, respectively. 88.4% and 6.2% of samples were lower than 10 g kg⁻¹ or 10 ~ 30 g kg⁻¹ in CaCO₃ content. Soil pH, Ca²⁺, Mg²⁺ and CaCO₃ were differed with different parent materials. Soil pH and Mg²⁺ contents of paddy soil and lime soil were significantly higher than those of other soil types. The differences of pH, Ca²⁺ and Mg²⁺ in regions were larger than that of CaCO₃. Correlation analysis showed that there were significant positive correlations among pH, Ca²⁺, Mg²⁺ and CaCO₃ (P < 0.01), and the linear regression model of pH with Ca²⁺, Mg²⁺ and CaCO₃ was as follows: pH = 5.065+0.393Mg²⁺+0.081Ca²⁺+0.001CaCO₃ (R² = 0.578, P < 0.001, MAE = 0.58, RSME = 0.71).

  Conclusion  The contents and distribution of soil pH, Ca²⁺, Mg²⁺ and CaCO₃ in Guizhou tobacco-planting fields are affected by parent materials, soil types and regions, and pH is affected by Ca²⁺, Mg²⁺ and CaCO₃. For soil pH adjustment and the application of calcium and magnesium fertilizers, soil pH, Ca²⁺, Mg²⁺ and CaCO₃ should be simultaneously considered due to their close relationships.