An evaluation of chemical methods for extracting copper from rice soils

Abstract

Rice (Oryza Sariva L. CV. Lemont) was grown on 19 soils, and eight extractants were evaluated for determining the availability of Cu to rice plants. Correlation aalyses were employed as criteria for evaluating method that would provide the best index of Cu availability. The order of removal of Cu from soils was: 0.5 N HC1 + 0.05 N A1C13 > 0.5 N HNO3 > 0.5 n HC1 > EDTA + NH4 OAc > 0.1 N HC1 > EDTA + (NH4)2co3 >> DTPA-TEA, pH 7.3 >>> 1 N NH4 OAc, pH 4.8. Uptake of Cu by rice plants was significantly correlated with soil Cu. Among the eight extractants evaluated, Cu extracted with DTPA-TEA, pH 7.3 was better related to the concentration (r = 0.563*) and uptake (r = 0.673**) of Cu by rice plants grown on the soils with different chemical and physical properties. A significant negative correlation was found between the concentration of Cu in rice plants and the organic matter content of the soils. Each one percent increase in the organic matter of the soils resulted in a corresponding decrease of approximately one mg/kg in the concentration of Cu i the rice-plant tissue. Multiple regressions of extractable Cu by eight methods with soil organic matter content accounted for from 53.4 to 70.0% of the variations in the prediction of the concentration of Cu in the rice plants. Combinations of other soil chemical properties measured with extractable Cu did not significantly improve the predictability.