Acidification Characteristics And Trend Of Red Soil From Different Parent Materials

Soil parent materials and vegetation types are two main factors that affect soil acidification. To investigate changes in pH, soil exchangeable acidity, soil cation exchange capacity, soil exchangeable base cations and soil base saturation at different depths of soil derived from different parent materials and different vegetation types will be significant for preventing soil acidification in regions. A series of soil samples at depths of 0-20, 20-40, 40-60, 60-80 and 80-100 cm were collected from 18 sites with 7 parent materials(Quaternary red earth, Red sandstone, Plate shale, Granite, River alluvial material, Limestone and Purple shale) under 4 vegetations(Imperata cylindrica meadow, Masson pine forest, Slash pine forest, and Broadleaf forest), in Qiyang county, Hunan province. The main results and conclusions were as blew:(1) Profile distribution of soil pH under 4 vegetations were various from each other. The pH 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 kinds of neutral soil, which pH were below 8.0 and above 7.0, Limestone soil was a kind of strongly alkaline soil, which range of pH was 8.46-8.72. Soil pH significantly increased with soil depths increasing at 0-100 cm layers, for Granite red soil, River alluvial material soil and Purple shale soil under Imperata cylindrica meadow, the increase amplitude of pH were higher than soil from other parent materials, but no change for Plate shale red soil. For Quaternary red earth red soil and Red sandstone red soil under forest, the increase amplitude of pH were higher than soil from other parent materials, but no change for Plate shale red soil. Soil exchangeable acidity had the opposite change trend as compared with soil pH. For red soils under Imperata cylindrical meadow, soil exchangeable acidity of Quaternary red earth red soil is higher than other parent materials. For Quaternary red earth red soil under forest, the decrease amplitude of soil exchangeable acidity was much larger than other parent materials, but no change for Plate shale red soil. For soil under Imperata cylindrical meadow, the difference of pH and soil exchangeable acidity between 60-80 cm layer and 80-100 cm layer were not significant. For soil under forest, the differences in soil pH and soil exchangeable acidity at 0-40 cm layers were much larger than that at 60-100 cm layers. Soil acidification was estimated by the difference in soil pH between surface layers(0-20 cm layers under Imperata cylindrical meadow or 0-40 cm under forest) and 60-100 cm layers.(2) For the surface layers of soil under vegetation types except Broad leaf forest, soil exchangeable base cations and soil base saturation of Granite red soil were significantly higher than other parent materials. For the surface layers of soil under Imperata cylindrical meadow and Slash pine forest, soil cation exchange capacity of Granite red soil was significantly higher than other parent materials, but for soil under Masson pine forest, soil cation exchange capacity of Red sandstone red soil was significantly higher than other parent materials. For soil under Broadleaf forest, soil exchangeable base cations, soil cation exchange capacity and soil base saturation of Plate shale red soil were all significantly higher than other parent materials. Soil exchangeable base cations, soil cation exchange capacity and soil base saturation were all decreased with soil depths increasing at 0-100 cm layers.(3) It is considered that the change of pH in wasteland is small by the long-term fertilization experiment, the pH in wasteland can be used to calculate the soil acidification rate of red soil from Quaternary red earth in the case of without the initial p H. The average acidification rate of Quaternary red soil is 1.02 kmolH+/hm2/a, especially under Slash pine forest, The average acidification rate of Quaternary red earth red soil is 1.65 kmolH+/hm2/a, So we should do more to prevent soil acidification in Quaternary red earth red soil under Slash pine forest. Soil acidification rate of other parent materials were caculated by the difference in soil pH between surface layers(0-20 cm layers under Imperata cylindrical meadow or 0-40 cm under forest) and 60-100 cm layers. For the 7 parent materials under Imperata cylindrical meadow, the acidification rate of Granite red soil(1.30 kmolH+/hm2/a) is more higher than other parent materials, and the soil pH will needs fifteen years drop to 4.0. The acidification rate of Red sandstone red soil was 0.40 kmolH+/hm2/a, soil pH will needs ten years drop to 4.0 because of the lower initial pH(4.31), so we should do more to prevent soil acidification in Red sandstone red soil and Granite red soil. For the 4 parent materials under forest, the highest average acidification rate was observed in the red soil derived from Granite(1.01 kmolH+/hm2/a), and the lower was found in red soils from Red sandstone(0.35 kmolH+/hm2/a), but no acidification for Plate shale red soil. The acidification rates of red soils with the 3 vegetations were in the following order: Slash pine forest>Masson pine forest>Broad leave forest. So we should do more to prevent soil acidification under Slash pine forest.