Propensity of Soils to Develop Redoximorphic Color Changes

Most soils with seasonally high water tables exhibit redoximorphic features, such as Fe depletions and concentrations. Some soils formed from red parent materials apparently are less typical in their behavior and have in this sense been described as problematic. Regulatory guidelines have mentioned such problematic red soils, and the Field Indicators of Hydric Soils in the United States attempts to address the issue by using test indicator TF2. This study was undertaken in an attempt to develop an approach for quantifying the inherent tendency of soils to form redoximorphic features under reducing conditions. Thirty soils from diverse parent materials in the Mid‐Atlantic region was studied, including 13 thought to be problematic soils formed from red parent materials. Samples were treated using a citrate‐buffer and Na dithionite at room temperature (25°C) for periods of time ranging from 0.5 to 72 h, and also at 80°C for 4 h. Colors were measured using a digital colorimeter to document changes in Munsell hue, value, and chroma. By comparing initial soil colors with those measured under the treatments of 25°C for 1 h and at 80°C for 4 h, a color change propensity index (CCPI) was developed that effectively discriminated between soils which were and were not thought to be problematic. The utility of the CCPI was tested using 14 additional soil samples, six of which came from outside the Mid‐Atlantic region. Recommendations are made to differentiate between problematic and nonproblematic soils based on values of CCPI.