Objectives To investigate changes in pH at different depths of soil derived from seven parent materials to help prevent soil acidification.

Methods Soil samples at layers of 0–20, 20–40, 40–60, 60–80 and 80–100 cm were collected from seven sites with different parent materials (Quaternary red earth, Red sandstone, Plate shale, Granite, River alluvial material, Limestone, and Purple shale) under Imperata cylindrica meadow, in Qiyang County, Hunan Province. Soil pH, soil acid and alkaline buffering capacity, soil organic matter, soil cation exchange capacity, soil specific surface area, and particle size were measured, and soil acidification was estimated by the difference in the soil pH between 0–20 cm and 60–100 cm layers.

Results The pH values of red soil from Quaternary red earth, red sandstone, plate shale and Granite were below 6.0, river alluvial material soil (pH 7.37–7.87) and purple shale soil (pH 7.41–8.00) were neutral with pH 7.0–8.0, and limestone soil was strongly alkaline with pH 8.46 – 8.72. For all the seven parent materials, the average acidification rate of red soils was in the order: purple shale soil > river alluvial material soil, granite red soil > Quaternary red earth red soil, and red sandstone red soil > limestone soil, plate shale red soil. Based on analysis of pH, soil acid and alkaline buffering capacity, soil organic matter, soil cation exchange capacity, soil specific surface area and particle size, no key factors were found in the seven parent materials that led to soil acidification. However, soil cation exchange capacity was found to be the key factor for soil acidification in four parent materials, including Quaternary red earth, red sandstone, plate shale and granite.

Conclusions Soil cation exchange capacity is negatively correlated with the soil acidification, which is one of the main factors limiting the acidification in four parent materials, including Quaternary red earth, red sandstone, plate shale, and granite.