COPPER BIODISPONIBILITY IN CALCAREOUS SOI L SAMPLES - .1. CHEMICAL FRACTIONATION OF COPPER

The biodisponibility of copper is usually measured by chemical reagent s such as EDTA. However, evidence of the cupric deficiency for plants may be observed without the chemical test for it. Thus the aim of this study was to apply classical sequential extraction procedures, used i n environmental studies, in order to obtain a chemical fractionation o f copper and to examine the possible relations between these fractions and the biodisponibility of copper. The study was performed on calcar eous soil samples. The soil samples were collected in Eastern France a nd correspond to an agronomical assay to study copper deficiency on ca lcareous soils. The results of the copper fractionation are described here. In a second paper, the copper biodisponibility related to this f ractionation will be discussed. The fractionation of copper in calcare ous soil samples reveals the importance of the last fraction (the resi dual fraction): about 80 % of the copper of the studied samples is fou nd in this fraction. Applied to soil having received copper supplement , the same procedure of fractionation gave similar results: 60 % of ad ded copper was found to be in the residual fraction. In order to Compa re the results of this fractionation with the amounts of copper extrac ted by EDTA, single extraction with EDTA were also performed. This che mical reagent extracts more copper than the first four extractions of the sequential extraction procedure.