A Study of Extractable Soil Cobalt in Soils of the Southeastern United States

Abstract The relationship between 2.5% acetic acid‐dithizone extractable soil cobalt and the amount of cobalt in black gum leaves, a cobalt indicator, was investigated for 71 widely distributed soils of the southeastern United States. The soil samples were from both good areas and areas where cobalt deficiency in ruminants would be expected on the basis of previous analyses. The extractable cobalt values appeared to separate the Ground‐Water Podzols, the Humic‐Gleys and the Low Humic‐Gleys from the better drained Regosols and Red‐Yellow Podzolic soils studied. At comparable cobalt concentrations in the black gum, the extracted cobalt was less from the imperfectly to poorly drained soils than from the well‐drained soils. For each of the two broad groups of soils, a significant correlation was obtained between extractable soil cobalt for the A 1 horizon and the cobalt concentration in the black gum. Because of the variability in horizon thickness among the different soils, the cobalt values were calculated for the 0‐ to 6‐ and 0‐ to 12‐inch depths. The correlation between these values and plant cobalt was also good. The acetic acid‐dithizone extractable cobalt appears useful in indicating areas of potentially low soil cobalt in the Southeast where deficiency in cattle or sheep might be a problem.