Soil solutions were isolated by centrifugation of moist soil taken from the root-zone of field-grown barley plants and bulk soil from adjacent fallow areas. Low concentrations of Cu, Mn, Zn and Co were found in soil solutions in late winter with increases in spring and early summer. Discrete maxima are generally achieved at some time between May and early July. The precise timing of such maxima appears to depend on the extent of the development of the growing crop and on seasonal influences. The extent to which micronutrient concentrations increase in fallow soils is less than in the root-zone soil solutions although similar trends occur. It is suggested that the increased micronutrient concentrations might result from their mobilization from insoluble forms by biologically produced chelating ligands.

Stability constants describing Cu2+ combination with three natural and one synthetic polycarboxylates were calculated from pH measurements alone, and using a Cu2+ ion selective electrode. Good agreement between the two methods justified the theory for polymer-cation association. The results were consistent with the formation of a single complex CuL2 over a fairly wide range of metal-ligand (L) ratios. The stability constant ( $, ) that was independent of polymer charge allowed the prediction of copper speciation in soil solution as a function of pH and soluble organic matter.