Indicator of reduction in soil (IRIS): Evaluation of a new approach for assessing reduced conditions in soil

Research and management of wetlands often requires the documentation of reducing soil conditions. Documentation of reduction in soils by measuring oxidation-reduction (redox) potentials using Pt electrodes is often difficult because of the time and cost involved in employing these techniques. This study evaluated a new procedure called Indicator of Reduction in Soil (IRIS) that has been recently developed to assist in the detection of reduced soil conditions. Polyvinyl-chloride (PVC) tubes coated with a ferrihydrite paint were inserted into the upper 50 cm of the soil for periods of 12 to 32 d. Soil redox potentials, water table height, and soil temperature were measured concurrently. Upon removal, the tubes were analyzed to assess the loss of ferrihydrite paint from the tube surface. When ferrhydrite paint was substantially depleted from 20% of the area of the IRIS tube, 87% of the observations at the corresponding depth indicated the soil was reduced. When ferrhydrite paint was substantially depleted from 30% of the area of the IRIS tube, essentially all of the soil observations at corresponding depths showed that the soil was reduced. Although not without complications, IRIS tubes appear to be a promising new alternative to traditional methods used to identify reducing conditions in soil.