Characterization of Placic Horizons in Ironstone Soils of Louisiana, USA

Placic horizons, defined as thin, wavy, hardened layers of iron and organic matter, are rare within the United States, occurring only in Washington, Alaska, and Hawaii. While ironstone is common in many soils of the southeastern United States, it is not known to contain appreciable organic matter. As a pilot study evaluating the justification for a larger study on ironstone in Louisiana, a 40 m lateral exposure with suspected placic horizons was evaluated in Vernon Parish, Louisiana. Results of laboratory analysis show elevated levels of iron and organic matter in the suspect horizons that meet the criteria of placic horizons as defined by the Soil Survey Staff. Based on the results of this study, additional evaluation of multiple pedons with similar features is warranted. Should additional pedons demonstrate similar properties, a new great group of ‘Petrudepts’ would be needed to describe both the placic horizons in the pedon and the udic moisture regime in which they occur.