Modification of the NH4HCO3-DTPA Soil Test to Omit Carbon Black1

Abstract

3 Recently Soltanpour and Schwab developed an NH4HCO3-DTPA (AB-DTPA) soil test to simultaneously extract NO3, P, K, Zn, Fe, Mn, and Cu. In this test carbon black was used to clear the extract for the chromotropic acid method of nitrate determination. However, use of carbon black was inconvenient due to its staining and sometimes contaminative properties. The purpose of the study reported here was to determine the effect of the elimination of carbon black from the AB-DTPA test on the extractable levels of P, K, Zn, Fe, Mn, and Cu. The results indicated that carbon black adsorbed Fe-, Mn-, and Cu-DTPA, but did not affect the levels of P, K, and Zn in the AB-DTPA extracts. Regressions of the modified AB-DTPA test (no carbon black) on the DTPA test for Zn, Fe, Mn and Cu were run. These regressions showed that the levels of AB-DTPA-extractable Zn, Fe, Mn, and Cu. © 1979, Taylor & Francis Group, LLC. All rights reserved.