Response of five Chinese forest soils to acidic inputs: batch experiment

Soils in southern China are in danger of being acidified due to the impact of long-term severe acid deposition. This paper presents the results of a batch experiment with five forest soils (two horizons from each) collected from five regions in southern China. The primary objective was to determine and compare the responses of these forest soils to acid deposition. Each soil sample was extracted 15 times with deionized water or one of three acidic extractants made of dilute mixed acids of H2SO4 and HNO3, and solutions of CaSO4, MgSO4 and NH4NO3. The trends in ion concentrations and pH in the soil extracts, and the changes in major soil properties such as pH, exchangeable base cations, exchangeable aluminium, effective cation exchange capacity (CECeff) and base saturation (BS) are discussed. In addition to exchangeable aluminium (Al-ex), soil Al was extracted with CuCl2, pyrophosphate, and oxalate solutions (Al-c, Al-p, and Al-ox, respectively). Considering both soil and soil water, the results indicate that acid deposition has the largest effects on the soils from Fujian and Nanchang, then followed by the soils from Hunan and Chongqing, while the effects on the Guiyang soil are probably less serious. The release of aluminium (Al-rel, i.e., the total amounts in extracts) was highly correlated to soil water pH and either of the aluminium pools, Al-p or Al-ox. For the aluminium mobilization (Al-mob, i.e., the sum of the aluminium release and the change in exchangeable aluminium) the best fit was obtained by using soil pH and the Al-ox pool. Soil organic matter seemed to play an important role in both aluminium release and aluminium mobilization. For two of the soils (Guiyang and Nanchang), the results were in excellent agreement with the values from previous column experiment with similar solutions. (C) 1998 Elsevier Science B.V. All rights reserved.