Effect of slaked lime and gypsum on acidity alleviation and nutrient leaching in an acid soil from Southern China

A soil column experiment was made to study the effects of slaked lime (Ca(OH)(2)) and gypsum (CaSO4. 2H(2)O) on soil acidity, soil solution chemistry and nutrient leaching in an acid soil from Southern China. Results showed that application of sufficient slaked lime to initially increase the pH of the topsoil by 1 unit caused an increase in pH to 5 cm deeper than the layer of application as a result of bicarbonate leaching. With leaching of Ca from slaked lime or gypsum from the topsoil to the subsoil there was a decrease in exchangeable Al in the subsoil. Surface application of slaked lime or gypsum or both decreased the activity of toxic Al and increased AlSO4+ activity in the subsoil solution. The Ca added in slaked lime or gypsum was accounted for by the increase in exchangeable Ca over the soil profile and the leaching loss. By contrast there was a negative balance of extractable sulfate and aluminum in the soil, indicating the formation of precipitates. There was little mineralisation of N and formation of NO3- under the conditions of the experiment. The leaching of cations in this soil treated with slaked lime or gypsum was driven by the dynamics of sulfate.