SOIL AND WATER-TABLE MANAGEMENT EFFECTS ON ALUMINUM DYNAMICS IN AN ACID SULFATE 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 a luminum dynamics during the dry season and the first three weeks of th e rainy season 1994 were studied in field and lysimeter conditions in an acid sulphate soil, in Mekong Delta, Vietnam. More acidity was prod uced in the subsoil when the water table was maintained at 60 and 90 c m compared with 30 cm deep. The amount of aluminum that accumulated in the topsoil during the dry season was linearly proportional to the cu mulated evaporation. Straw mulching significantly lowered the dry seas on aluminum accumulation (0.6 cmol(+) kg(-1)) in comparison with nonmu lching treatment (2.0 cmol(+) kg(-1)). Surface ploughing also reduced aluminum accumulation, but the reduction was not statistically signifi cant compared with nonploughed plots. Rains at the beginning of the ra iny season raised the water table rapidly to the topsoil layer. Alumin um brought up with the rising water table greatly increased the toxici ty level in the topsoil and nullified the positive effects of dry seas on soil treatments. Controlling groundwater level to below the topsoil and enhancing the leaching effects at the beginning of the rainy seas on are important for retaining the effects of the dry season treatment s. (C) 1998 Elsevier Science B.V.