Cobalt and manganese relationships in New Zealand soils

Abstract

Total soil concentrations of cobalt (Co) and manganese (Mn) were determined in a range of pastoral soils sampled from four different regions of New Zealand. Concentrations of Co and Mn extracted from soils with 0.02 M Na2H2EDTA (pH 7.0) and with 0.05 M CaCl2 were also determined, and, in the case of Co, were determined using both air-dried and field-moist samples. Relationships between total and extractable soil Co and Mn concentrations, and other soil properties, were examined by means of statistical correlation and regression analysis. There were significant correlations between total and EDTA-extractable Co and Mn in both top- and subsoils, indicating a strong geochemical association between Co and Mn in soils during their development. As assessed by CaCl2 extraction, there were only small proportions of soil Co and Mn present as soluble and exchangeable forms in New Zealand soils. It was observed that soluble Co and Mn concentrations could be reasonably well predicted from soil pH and the respective EDTA-extractable metal concentrations. Air-drying of soils increased CaCl2-extractable Co concentrations by an average of five-fold, indicating the likely sensitivity of soluble soil Co concentrations to soil water potential.