Reduction of Fe occurs when water moves through soil slowly. Reduction of Fe does not occur when water flows quickly. Water moves fast through sands and gravels, and on sloping lands. Fast moving water carries O2, which prevent Fe from being reduced. When water tables rise due to rainfall alone, the water is aerated.
Reduction occurs after rainfall stops.
Two soils studied in Texas are compared. Watertables were measured weekly for two years, and the amount of Fe reduction that occurred was determined for one year. H. Color 1. Some soil parent materials never had Fe2O3, and have always been gray. Wet soils usually have both gray colors and reddish colors.