Abstract: 【Objective】Soil parent materials and vegetation types are two main factors that affect soil acidification. To investigate changes in pH and soil exchangeable acidity at different depths of red soil derived from different soil parent materials and different vegetations will be significant for preventing soil acidification in regions with red soil.【Method】A series of soil samples at depths of 0-20, 20-40, 40-60, 60-80 and 80-100 cm were collected from 11 sites with 4 parent materials (Quaternary red earth, Red sandstone, Plate shale, and Granite) under 3 vegetations (masson pine forest, slash pine forest, and broadleaf forest), in Qiyang County, Hunan province. Soil pH and soil exchangeable acidity were determined, and soil acidification was estimated by the difference in soil pH between 0-40 cm and 60-100 cm layers. 【Result】 The pH of red soils derived from the 4 parent materials was below 6.0. For the 4 parent materials, the average pH of red soils at 0-40 cm layers were following the orders: Granite red soil＞Red sandstone red soil＞Quaternary red earth red soil＞Plate shale red soil; the average pH of red soils under the 3 vegetations were following the orders: masson pine forest＞slash pine forest＞broadleaf forest. But exchangeable acidity showed the opposite trend. For Quaternary red earth, soil pH significantly increased with soil depths increasing at 0-40 cm layers, but the pH of red soils derived from other parent materials decreased; soil exchangeable acidity had the opposite change trend as compared with soil pH. At layers of 40-100 cm, the average pH of red soils derived from the 4 parent materials werein the following order: Granite red soil＞Quaternary red earth red soil＞Red sandstone red soil＞Plate shale red soil; red soil pH under the 3 vegetations were in the following order: slash pine forest＞masson pine forest＞broadleaf forest. But, exchangeable acidity showed the opposite change trend. There were increasing trends in red soil pH at depths from 40 cm to100 cm for Red sandstone, Quaternary red earth, and Granite, but no change for Plate shale. Exchangeable acidity showed the opposite. For the 4 parent materials, the average acidification rate of red soils were in the following order: Quaternary red earth red soil＞Red sandstone red soil＞Granite red soil＞Plate shale red soil. For the 3 vegetations they were in the following order: slash pine forest＞broadleaf forest＞masson pine forest. 【Conclusion】For red soils derived from the 4 parent materials under the 3 vegetations, the differences in soil pH and soil exchangeable acidity at 0-40 cm layers were much larger than that at 40-100 cm layers. For the 4 parent materials, the highest average acidification rate was observed in the red soil derived from Quaternary red earth at 0-40 cm layers, and the lowest was found in red soils from Granite and Plate shale. The acidification rates of red soils with the 3 vegetations were in the following order: slash pine forest＞broad leave forest＞masson pine forest.

Key words: red soil, pH, exchangeable acidity, acidification, soil parent materials, vegetation types