Studies on Soil Copper

Summary A method based on that used by McAuliffe et al . (1948) for phosphorus was developed for determining isotopically exchangeable copper in soils using the radioisotope 64 Cu. The authors are confident that, with a few exceptions, isotopic equilibrium in soil/solution systems is attained rapidly enough to overcome possible difficulties resulting from the short half‐life of this isotope. For the twenty‐four soils examined, amounts of isotopically exchangeable copper were found to be between 0.19 and 12‐24 μg g ‐I and represented between 2 and 21 per cent of the total soil copper. A correlation test and an experiment involving fractionation of labelled soils both demonstrated that the bulk of the isotopically exchangeable copper was located in the organic‐bound fraction. Not all copper specifically adsorbed by organic matter was readily exchangeable with 64 Cu : for one sample of organic material examined only 20 per cent of the adsorbed copper was isotopically exchangeable after 24 hours equilibration. The corresponding figures for clay materials and oxide material were found to be between 75 and 60 per cent.