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Abstract
A chemical equilibrium model of a typical plant nutrient solution was constructed and applied, in conjunction with an appropriate data base of equilibrium constants, to the program MINEQL. The output yielded the speciation of the metals in the nutrient solution. Additions of DTPA or EDTA were found to suppress the concentration of copper(II), zinc(II) and manganese(II) aquo ions, the relative decrease in concentration being more marked at pH 7.5 than at pH 4.3 in the case of DTPA but more marked at pH 4.3 than at pH 7.5 in the case of EDTA. These results were found to correspond to the trends observed in experimental observations on hydroponically cultivated bush beans. The results are interpreted in terms of the aquo ions of the three metals considered being the bioavailable species. The possible importance of copper(II)-hydroxy and other dissolved copper(II) species as bioavailable forms was considered but no clear conclusions could be reached.