Comparison of Two Sequential Extraction Methods and the DTPA Method for the Extraction of Micronutrients from Acidic Soils.

Two sequential extraction methods (the modified BCR—Community Bureau of Reference, now the Standards, Measurement and Testing Program, of the European Commission—and the original Tessier) were compared for the assessment of various forms of copper (Cu), zinc (Zn), iron (Fe), and manganese (Mn) in 29 cultivated acidic soils of northern Greece. In addition, the different forms of the micronutrients extracted by the two methods were compared to the plant-available micronutrients extracted by diethylenetriaminepentaacetic acid (DTPA) and their relation to certain soil physicochemical properties was examined. Because the soils were acidic, the second step of the original method of Tessier (related to micronutrients bound to carbonates) was omitted. Consequently, four micronutrient fractions were assessed by both methods, namely water-soluble + exchangeable, bound to Fe-Mn oxides, bound to organic matter, and residual. Each of the two methods extracted different amounts of the same micronutrients in similar fractions, which amounts were significantly and positively correlated. The order of Fe and Mn distribution in the various fractions was similar in the two methods, within the same element, whereas Zn was slightly different and Cu was detectable only in the residual fraction of both methods. Clay and Fe-Mn oxide–bound Fe, cation exchange capacity (CEC), and organic matter–bound Fe were significantly and positively correlated in the case of the original Tessier method. In the modified BCR method, organic matter–bound Fe and Zn were significantly and positively correlated with CEC. In both methods, significant and positive correlation coefficients were found for the following relations: clay and Mn in the water-soluble + exchangeable fraction, organic C and organic matter–bound Mn, CEC and Mn in the three first fractions. The DTPA-extractable micronutrients were significantly and positively correlated with the respective micronutrients in the fractions bound to Fe-Mn oxides and bound to organic matter of the original method of Tessier for Zn; the fraction bound to Fe-Mn oxides of the same method for Fe; and the three first fractions of both sequential extraction methods for Mn. [ABSTRACT FROM AUTHOR]