Relations of Iron, Aluminum, and Carbon Along Transitions From Udults to Aquods.

Depth and morphological expression of Bh horizons were studied with respect to iron (Fe), aluminum (Al) & carbon (C) concentrations along four transects encompassing transitions from poorly-drained Aquods to better drained soils. The Bh horizons of Aquods were well-expressed, but Bh horizons along the transition toward better –drained soils became shallower and less-well expressed, ultimately fading into the surface horizon. Organically-complexed and amorphous Fe and Al were extracted by pyrophosphate and ammonium oxalate, respectively, and measured by inductively coupled plasma spectrometry. Pyrophosphate-extractable C and total C were measured by flash combustion. Extractable Al in Bh horizons correlated positively with extractable- and total C as well as with measures of Bh expression and depth to upper boundary. However, extractable Fe correlated negatively with these variables. Weak Bh horizons of better-drained soils had higher Fe concentrations and Fe/Al ratios than did more strongly expressed Bh horizons of poorly-drained soils. Results suggest that pedogenic processes fostering Bh formation in Aquods are hindered by the presence of Fe in the grain coatings of better drained soils.