Quantifying the acidification in Thai agricultural soils under acidic deposition

Soil acidification is unfavourable for agricultural production due to reduced availability of plant nutrients and decreased activity of soil microbes. This study quantifies the levels of soil acidification that result from different rates of acid deposition in three agricultural soils (Korat, Pak Chong and Phon Pisai soil series) of Thailand. In a laboratory experiment, acidic solutions (pH 5.0, 4.0, 3.5, 3.0, 2.5 and 2.0) and unpolluted water (pH 7.0) were sprayed on soil columns for a period of 45 days. Soil acidity was measured in different soil layers after the application of treatments. Acidic treatments caused significant (p<0.001) declines in soil pH in all the investigated soils. Soil acidity increased with decreases in pH levels of the applied solutions. Acidic solutions caused more acidification in the upper layers of the soils. Soil acidity development depended on the pH of the applied solution, soil texture and the cation exchange capacity of soils. Very good correlations were found between soil acidification and pH levels of the applied solutions, i.e. R 2 = 0.978 (Korat), R 2 = 0.982 (Pak Chong) and R 2 = 0.983 (Phon Pisai). Polynomial equations to characterize the relationships between the pH levels of the treatment solutions and the resulting soil pH levels were also developed using regression analyses.