Objectives Crop types and management modes are main factors influencing red soil acidification. Study of the acidify characteristics of red soil profiles under different land uses will provide reference for mitigating acidification of red soil in hilly regions.
Methods Soil samples developed from red sandstone under 4 land uses (paddy field, dry land, orchard, and forest land) were collected from different depths (0−20, 20−40, 40−60, 60−80 cm and 80−100 cm). The soil pH, exchangeable acid, amount of exchangeable base and salt base saturation were measured, quantitative comparison was conducted on acidification characteristics and their variation with depth and land use.
Results pH of red soil followed the following order: paddy soil (5.69) > dry land (4.71) ≈ orchard (4.74) > woodland (4.49). Exchangeable acid followed the order: woodland (6.54 cmol/kg), dry land (6.52 cmol/kg) > orchard (3.51 cmol/kg) > paddy (0.79 cmol/kg). Exchangeable base followed the order: paddy (4.47 cmol/kg) > dry land (1.97 cmol/kg) > orchard (1.26 cmol/kg) > woodland (0.48 cmol/kg). Salt base saturation followed the order: paddy (53.14%) > dry land (20.87%) > orchard (15.41%) > woodland (4.67%). With the increase of soil depth, soil pH increased gradually, but exchangeable acid did not change. Exchangeable base increased with soil depth, following the order: 60−100 cm (2.34 cmol/kg) > 40−60 cm (2.05 cmol/kg) > 0−40 cm (1.75 cmol/kg). Salt base saturation of paddy soil increased with depth, with 33.95% at 80−100 cm, 32.27% at 60−80 cm, 31.31% at 40−60 cm, 25.47% at 20−40 cm and 21.08% at 0−20 cm. Soil pH under paddy and orchard uses had a significant negative correlation with exchangeable acid, but a significant positive correlation with exchangeable base and salt base saturation. Soil pH under dry land use had a significant positive correlation with exchangeable base. Soil pH under woodland use had a significant negative correlation with exchangeable acid.
Conclusions At 0−40 cm soil depth, red soil acidity of woodland is the highest, followed by orchards and the dry land, while that of paddy is the lowest under four land uses. Red soil acidity has small variation at 40−100 cm depth. Red soil acidity can be improved by changing land use patterns, decreasing exchangeable acid content, and increasing total exchangeable base content and salt base saturation.
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