In a glasshouse pot experiment in Athens, Greece in 1989, 85Sr to calcium observed ratios (OR) based on the values of exchangeable Ca instead of soil Ca (ORexCa), were determined for crops or plant parts grown in eight soils widely differing in their physical and chemical properties. Compared to the values of concentration ratio (CRs) the values of ORexCa did not show as wide variation with the soil type. They were relatively constant and usually not related to soil properties. The ORexCa values were essentially the same as OR values for the non-calcareous soils and much smaller than the OR values for calcareous soils, considering as soil Ca in the calculation of OR, the sum exchangeable, watersoluble and CaCO3 Ca.
The values of 85Sr/Ca + Mg observed ratios (ORexCaMg) were just as good as the ORexCa values, while those of 85Sr/Ca + Mg + K + Na (ORex bases) showed more variation.
Highly significant (P <0·01) correlations were observed between the fractions of the observed ratios ORexCa, ORexCaMg and ORex bases, for each crop or plant part tested.