Laboratory and Greenhouse Evaluation of Five Chemical Extractants for Estimating Available Copper in Selected Calcareous Soils of Iran

Abstract

Documented plant responses to copper (Cu) are rare and consequently Cu soil tests have not received much individual effort. However, soil extraction techniques to measure the status of available Cu for plants are important in the diagnosis of deficiency or toxicity. In the present study, DTPA-CaCl₂, EDTA-NH₄OAc, EDTA-(NH₄)₂CO₃, DTPA-NH₄HCO₃, and EDTA were evaluated for their relative efficiency to extract Cu from 26 soil series with a wide range of chemical properties. Wheat (Triticum aestivum L.) was used as a test crop. The results showed that Cu extractability decreased in the order: EDTA-(NH₄)₂CO₃, DTPA-NH₄HCO₃, EDTA, EDTA-NH₄OAc, and DTPA-CaCl₂. Significant positive correlations were found between extractable Cu among the five extractions. Stepwise multiple regression equations showed that organic matter (OM) and clay content followed by cation exchange capacity (CEC) and calcium carbonate equivalent (CCE) were the most influential soil characteristics affecting extractable Cu. Mean top dry weight, Cu concentration and Cu uptake were significantly higher in Cu-treated plants than those in untreated plants. Significant correlations were found between Cu extracted with DTPA-CaCl₂ and EDTA-(NH₄)₂CO₃ and Cu uptake by wheat. However, the two extractants were not adequately efficient to predict Cu uptake with each accounting for only about 30% of the variation. Among soil properties tested, clay, pH, OM, and CCE correlated negatively and CEC positively with wheat top dry weight, whereas, pH, CEC, and CCE related positively and clay, and OM negatively with Cu uptake. In conclusion, it appears that none of the five test procedures in view of their relatively low coefficient of determinations with plant response proved to be a promising extractant for the determination of available Cu in the soils tested.

Keywords:

• Cu soil tests
• Extractable Cu
• Plant Cu
• Soil characteristics
• Wheat

Acknowledgments

Authors are grateful to the Shiraz University Research Council for approval and providing the financial support for Research Project No. 78-AG-1238-667.