Response of acid sulphate soils to different liming treatments I. Solubility of sulphate and phosphate

In a preliminary laboratory experiment, samples from three cultivated and three virgin acid sulphate soils (pH   CaCl   23.9‐4.7) were treated with water or equivalent amounts of Ca(OH) 2 or KOH and incubated at about field capacity for three months. Both base treatments (133 meq/kg) similary reduced soil acidity and, thus, the same influence on the pH‐dependent biological and chemical reactions was concluded. The liming‐induced mineralization of organic S seemed to account for increased extratability of sulphate, being in most soils of the same magnitude in both treatments. Inversely, the solubility of P hardly was affected by the decomposition of organic matter but rather by the reactions of inorganic P. KOH markedly raised water‐soluble P, whereas Ca(OH) 2 did not. The results of a rapid extraction test suggested that the poorer extractability of P in the soils amended with Ca(OH) 2 could partly be ascribed to a higher Ca saturation and its impact on the electrochemical properties of charged surfaces. In addition, a higher base‐associated ionic strength created by Ca 2+ was of great importance in reducing the P desorption in the Ca(OH) 2 ‐ treated soils.