Documenting Reducing Conditions in Soils. Martin C. Rabenhorst Environmental Science and Technology University of Maryland. Significance of documenting reducing conditions in soils?. To demonstrate that a soil meets the Technical Standard for Hydric Soils
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Martin C. Rabenhorst
Environmental Science and Technology
University of Maryland
Redox potential measurement using Pt electrodes
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Where 10% of the iron oxide paint was removed, the soils were reducing in 82% of the sections while in 18% of the cases, the soil was oxidized.
Where 20% of the iron oxide paint was removed, the soils were reducing in 89% of the sections while in 11% of the cases, the soil was oxidized.
Where 25% of the iron oxide paint was removed, the soils were reducing in 100% of the sections.
Percentage of Observations
Oxidized or Reduced by the TS
Castenson, K. L. and M. C. Rabenhorst. 2006. Indicator of reduction in soil (IRIS): Evaluation of a new approach for assessing reduced conditions in soil. Soil Sci. Soc. Am. J 70: 1222-1226.
(FeCl3 titrated to pH 7.5 with KOH)
0.75 0.6 0.5 0.4 0.35 0.3 0.25 0.2 0.15 d-spacing nm
2 broad peaks for ferrihydrite
Feo/Fet = proportion of Ferrihydrite
1-Feo/Fet = proportion of Goethite
Rabenhorst, M. C. and S. N. Burch. 2006. Synthetic Iron Oxides as an Indicator of Reduction in Soils (IRIS). Soil Sci. Soc. Am. J. 70: 1227-1236.
15% Goethite; 85% Ferrihydrite 1:5.7
44% Goethite; 54% Ferrihydrite 1:1.3
Blank (peak from Fe
in detector window)
(Total Counts) / (Baseline counts) – 1.0
Sample from “yellow” area on IRIS tube
RICH IN GOETHITE
-10 -5 0 5 10
Means of four replicate analyses
Rabenhorst, M. C., D. W. Ming, and R. V. Morris. 2006. Synthesized Iron Oxides Used as a Tool for Documenting Reducing Conditions in Soils. 18th World Congress of Soil Science, Philadelphia, PA. July 9-15, 2006.
Rabenhorst, M. C., R. R. Blank, and B. R. James. 2006. Reduction of Iron Oxides in Wetland Soils. 18th World Congress of Soil Science, Philadelphia, PA. July 9-15, 2006.
Mesocosms filled with two different soil materials (Indiantown A horizon and Berryland A horizon) and each containing 36 IRIS tubes representing 4 replicates of 9 different paints