Free Iron Sources in an Aquult‐Udult Sequence from North Carolina

Soils with deep water tables in the middle Coastal Plain of North Carolina contain more iron extractable by oxalate, dithionite, and HCl, as well as more total iron than do soils with shallow water tables. The iron increase is relatively uniform from the sites with shallow water tables to those with the deep water tables at three locations studied. These changes in iron content are not produced by differential weathering of iron‐bearing minerals. The water‐table history and related oxidation‐reduction regime of each site is believed to be the major factor controlling the amount of extractable iron. All soils had shallow water tables before the Coastal Plain was dissected. There probably was little loss of iron during the early periods of formation, although some of the noncrystalline iron was reduced, because there was little water movement through the sediments. Once the landscape was dissected, soils near the stream had deep water tables and nearly continuous oxidizing conditions. But soils in the centers of the divides would continue to have periodic reducing conditions with consequent removal of soluble materials by a downward flow of ground water. The changes in iron contents in the soils studied are related to the losses of iron at each site. Very little iron may have been lost from soils that had deep water tables during most of their development. At these sites, the major changes that have taken place are translocations of iron within the solum.