Soil and water table management effects on aluminum dynamics in an acid sulphate soil in Vietnam

Understanding the process of toxicity accumulation in the root zone is important in improving the quality of acid sulphate soils. The effect of straw mulching, soil surface ploughing and water table depths on aluminum dynamics during the dry season and the first three weeks of the rainy season 1994 were studied in field and lysimeter conditions in an acid sulphate soil, in Mekong Delta, Vietnam. More acidity was produced in the subsoil when the water table was maintained at 60 and 90 cm compared with 30 cm deep. The amount of aluminum that accumulated in the topsoil during the dry season was linearly proportional to the cumulated evaporation. Straw mulching significantly lowered the dry season aluminum accumulation (0.6 cmol(+) kg(-1)) in comparison with nonmulching treatment (2.0 cmol(+) kg(-1)). Surface ploughing also reduced aluminum accumulation, but the reduction was not statistically significant compared with nonploughed plots. Rains at the beginning of the rainy season raised the water table rapidly to the topsoil layer. Aluminum brought up with the rising water table greatly increased the toxicity level in the topsoil and nullified the positive effects of dry season soil treatments. Controlling groundwater level to below the topsoil and enhancing the leaching effects at the beginning of the rainy season are important for retaining the effects of the dry season treatments. (C) 1998 Elsevier Science B.V.