Single and Sequential Extraction of Cadmium in Some Highly Calcareous Soils of Southwestern Iran

Thirty-two surface soil samples with different physical and chemical properties were collected from calcareous soils of arid regions of Khuzestan Province, Southwestern Iran. Actual and potential cadmium (Cd) bioavailability was assessed by means of a greenhouse study, two different single extractions: 0.005 DTPA and 0.05 EDTA and two sequential extraction procedures: modified five-step Tessier method and the three-step BCR method. Extraction results were correlated with grain Cd uptake by Durum wheat (Triticum durum L.) grown under greenhouse conditions. Cadmium in the durum grain ranged from 0.064 to 0.273 mg kg(-1). The results showed better suitability of DTPA extraction in these highly carbonated soils than EDTA extraction for predicting Cd phytoavailability. DTPA -extractable Cd was positively related to soil electrical conductivity (p < 0.01, r = 0.65). Cadmium was predominantly associated with carbonate fraction in these soils (Tessier procedure 40% and BCR 44%). 1 M NH4OAc which extracted the soluble + exchangeable fraction in the Tessier scheme may also provide useful information on Cd availability in studied soils.