A Comparison of Analytical Methods for Soil Zinc

Abstract Soils from 92 fields in California were analyzed for extractable Zn by four methods, namely, ammonium acetate‐diphenyl‐thiocarbazone (dithizone), diethylenetriaminepentaacetic acid (DTPA), 0.1 N HCl, and disodium ethylenediaminetetraacetate (Na 2 EDTA). Each soil was tested in the greenhouse for plant response in relation to Zn applications. All four methods exhibited a high degree of correlation with each other; the highest correlation coefficient was obtained for the comparison of dithizone with DTPA. Calculated predictive values for DTPA, dithizone, 0.1 N HCl, and Na 2 EDTA were 83, 79, 73, and 72%, respectively, for the 92 soils studied. On this basis the DTPA is preferable to the others and the critical level is approximately 0.5 ppm Zn. For some soils, more than one method may be required to properly characterize the Zn status. The choice of method will depend upon the correlation with plant response, equipment and facilities available, and to some extent on the preference of the analyst.