Response of acid sulphate soils to different liming treatments II. Exchangeability of soil cations

Abstract

AbstractLiming‐induced changes in cation exchangeability were studied in six samples from acid sulphate soils (pH 3.9‐4.7) incubated with water or with equivalent quantities of Ca(OH)2 or KOH. The extractability of acid cation species susceptible to hydrolysis was shown to be affected not only by increased pH but also by the kind of the cation and related electrochemical properties of the base used. Both liming treatments practically eliminated the exchangeable Al. In the virgin soils, however, the polynuclear Al‐complexes formed by Ca(OH)2 treatment seemed to have been hydrolyzed further. The superiority of Ca(OH)2 was assumed to be due to the higher valency of its cation and its act of provoking a higher increase in ionic strength.The liming agents affected to varying extents also the extractability of base cations. Exchangeable soil K seemed to decrease by the KOH treatment and the soil Ca by the Ca(OH)2 treatment, whereas K and Ca were only slightly, if any, affected by the Ca(OH)2 and KOH treatments, respectively. Thus, the reductions were assumed to be attributable to other factors than increased pH. A fixation of K and a possible precipitation of Ca as CaSO4 were discussed. Ca(OH)2 decreased in all soil samples the exchangeability of Mg more than did KOH. The depression was not related to the Al polymerization and, thus, cannot entirely be ascribed to specific sorption on Al gel. The results imply that liming may affect base cation exchange reactions by neutralizing exchangeable Al of high bonding strength and by replacing it by cations of the liming agent.