Solubility of Co, Ni and Mn in Some Extractants in a Finnish Acid Sulphate Soil Area

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Abstract
Oats and barley grown in an acid sulphate soil area on the coast of the Gulf of Bothnia have exhibited exceptionally high concentrations of Co, Ni and Mn. The objective of this study was to identify the factors contributing to this phenomenon by examining 63 samples from acid sulphate soils and 35 samples from other soils of the area. The samples, taken from the plough layer, were extracted for determination of Co, Ni and Mn with aqua regia (total) or 0.5 M ammonium acetate—0.5 M acetic acid—0.02 M Na2-EDTA, pH 4.65 (AAAc-EDTA); Mn was also extracted with 1 M KCl. The two soil groups did not differ in terms of total Co, Ni or Mn but the amounts of AAAc-EDTA extractable Co and Ni, and KCl extractable Mn were two to three times greater in the acid sulphate soils than in the other soils. The amounts of Co and Ni extracted by both procedures were in close correlation with each other and with Mn. Total Co, Ni and Mn content and soil pH explained 58–69% of the variation of AAAc-EDTA extractable Co and Ni as well as KCl extractable Mn. It is postulated that, in addition to soil acidity, water saturation of the soil caused by insufficient drainage, has contributed to the high mobility and plant availability of Co, Ni and Mn in this acid sulphate soil area.