Albic Neoskeletans in Argillic Horizons as Indices of Seasonal Saturation and Iron Reduction

Significant periods of seasonal waterlogging in some soils of the Texas Coastal Plain have gone unrecognized because the soils lack low (≤ 2) chroma colors. A study was conducted in two soils along a forested toposequence of Alfisols to identify morphological features other than color that are indicative of ground water saturation and Fe reduction. The duration of saturation and Fe reduction had been determined previously for each soil of the toposequence. Iron nodules (> 2 mm diam) and neocutanic albic materials (albic neoskeletans) were sampled and their abundance determined. Albic neoskeletans were also characterized with respect to total Fe content, particle size distribution, and color. Sesquioxide nodules within portions of the argillic horizon had no consistent relationship to the soil structure and were found both in zones of Fe loss and accumulation. This indicated at least some nodules were relict features and that nodules could not be used for moisture regime identification in these soils. Albic neoskeletans along ped surfaces and root channels formed in place by a loss of clay and free Fe from the surfaces of macropores. Most albic neoskeletans were not overlain by other cutans and all evidence indicated they formed under the current moisture regime in each soil examined. Albic neoskeletan abundance was directly related to the duration of Fe reducing conditions, but not to the duration of saturation. Greatest development of these features occurred in a soil with a perched water table in horizons that were Fe reduced for 55 to 146 d. It is suggested that albic neoskeletans be used as diagnostic criteria for water saturation and Fe reduction despite their moist color chromas of 4 or less. It is proposed that albic neoskeletans be used, when low (≤ 2) chroma colors are absent, to identify aquic intergrades in Paleudalfs.