SALTS AND ACIDS AS DETERMINANTS OF THE SOLUTION COMPOSITION OF ACIDICFOREST SOILS - ANION EFFECTS

The study aimed at evaluating whether salt-induced mobilization of aci dity may be modified by the type of anion. For this purpose, the effec ts of different neutral salts on the solution composition of acid soil s were investigated. The results were compared with those of the addit ion of acids. Two topsoil (E and A) and two subsoil horizons (Bs and B w) were treated with NaCl, Na2SO4, MgCl2, MgSO4, HCl, and H2SO4 at con centrations ranging from 0 to 10 mmol dm(-3). With increasing inputs o f Cl- the pH of the equilibrium soil solution dropped, the concentrati ons of Al and Ca increased, and the molar Ca/(Al3+ + AlOH2+ + Al(OH)(2 )(+)) ratios decreased. These effects were the least pronounced when N aCl was added and the most at the HCl treatments. According to the rel ease of acidity, the topsoils were more sensitive for salt-induced soi l solution acidification whereas on base of the molar Ca/(Al3+ + AlOH2 + + Al(OH)(2)(+)) ratios, the salt effect seems to be more important f or the subsoils. Addition of SO42- salts and H2SO4 induced higher pH a nd lower Al concentrations than the corresponding Cl- treatments due t o the SO42- sorption, especially int he subsoils. The Ca/(Al3+ + AlOH2 + + Al(OH)(2)(+)) ratios were higher than those of the corresponding C l- treatments. In subsoils even after H2SO4 additions these ratios wer e not higher than those of the NaCl treatments. The results indicate ( I) that speculation about the effects of episodic salt concentrations enhancement on soil solution acidification not only need to consider t he ionic strength and the cation type but also the anion type, (II) th at salt-induced soil solution composition may be more crucial in subso ils than in topsoils, and (III) that in acid soils ongoing input of HN O3 due to the precipitation load may induce an even more acidic soil s olution than the inputs of H2SO4 of the last decade.