Fa. Khan et Te. Fenton, SECONDARY IRON AND MANGANESE DISTRIBUTIONS AND AQUIC CONDITIONS IN A MOLLISOL CATENA OF CENTRAL IOWA, Soil Science Society of America journal, 60(2), 1996, pp. 546-551
Redoximorphic features, saturation, and reduction of Fe are the essent
ial properties that define aquic conditions, Proposed colorimetric tes
ts for reduction of Fe did not respond in sola of a Mollisol catena fr
om central Iowa. The objectives of this study were to determine the di
stributions of redox-sensitive metals as potential indicators of aquic
condition and relate them to soil morphology and water table depth of
soils to differentiate aquic from nonaquic conditions. The variabilit
ies of different forms of extractable Fe and Mn throughout the soil pr
ofile and their relationships to aquic and nonaquic conditions were in
vestigated for five soils from a Mollisol catena in central Iowa, Sele
ctive dissolution methods were used to extract various forms of Fe and
Mn, There was a pronounced decrease in total Fe as the duration of sa
turation increased. With permanent saturation and presence of gray mat
rices in soil horizons, content of Fe-d and Mn-d (citrate-bicarbonate-
dithionite-extractable Fe and Mn) decreased, but Mn-d increased where
periodic saturation exists. The ratio of Mn-d/Fe-d with its depth func
tion in conjunction with water table data and soil morphology separate
d aquic from nonaquic conditions among members of the Mollisol catena
studied. Therefore, secondary Fe and Mn distributions within this Moll
isol catena are better indicators of aquic and nonaquic environments t
han the colorimetric tests for Fe2+. This ratio needs to be tested in
other areas and could be used as an alternate criterion instead of red
uction of Fe when a colorimetric test does not differentiate aquic fro
m nonaquic conditions.