We extracted 55 cultivated organic soils with (1) 0.5 M HC1 + 0.05 M A1C13, (2) 1.0 M NH4HCO3 + 0.005 M DTPA, (3) 0.005 MDTPA + 0.1 MTEA, (4) 1.0 M NH4OAC + 0.2 M EDTA, (5) 0.1 M EDTA, (6) 0.1 M HC1, (7) 2.5% HOAC, and (8) 1.0 M NH4OAC to compare the results with previously identified and quantified active (intensity factor) and reserve (capacity factor) forms of Cu, Fe, Mn, and Zn in the soils.
The intensity factor of Cu, Fe, Mn, and Zn in these soils was considered to be mainly H2O-soluble and Ca-exchangeable. For Cu and Fe, the capacity factor was chiefly composed of strongly complexed and sulfide-associated portions, and the capacity factor for Mn included readily reducible oxides and weakly or strongly complexed forms. For Cu, Fe, and Mn, only extractants 1 (HC1 + A1C13) and 2 (NH4HCO3 + DTPA) gave soil test values that were (1) greater than or equal to the intensity factor, (2) correlated with both the intensity and capacity factors of the soils, but (3) did not exceed the sum of the two factors. The effectiveness of extractants 1 and 2 for either Cu, Fe, Mn, or Zn was not adversely affected by the level of the other three elements. The two extractants thus met all criteria set in this study for a good, single soil test extractant for Cu, Fe, Mn, and Zn in the cultivated organic soils.
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