Soil Redox Potential: Importance, Field Measurements, and Observations

• Published in: Advances in Agronomy Vol. 94; pp. 1 - 54
• Main Authors: Fiedler, Sabine, Vepraskas, Michael J., Richardson, J.L.
• Format: Book Chapter Journal Article
• Language: English
• Published: United States Elsevier Science & Technology 01.01.2007; Elsevier BV
• Subjects: Agricultural science; Agronomy; Crop husbandry; Electrodes; field experimentation; literature reviews; measurement; Measurement techniques; Measuring instruments; methodology; Oxidation; Redox potential; redox reactions; Soil science, sedimentology; Soil testing; Soils
• ISBN: 0123741076; 9780123741073
• ISSN: 0065-2113; 2213-6789
• DOI: 10.1016/S0065-2113(06)94001-2

Reduction and oxidation measurements create important data for analysis of wet soils. These measurements are actually recordings of voltage (EH) over time between a reference electrode and a sensor electrode inserted into a soil. The sensor electrodes are usually made of platinum wire (Pt electrode). Hydric soils require a period of reduction, and these measures can provide the length of time that the reduction process is occurring. The voltage results from an exchange of electrons between a redox couple such as ferrous and ferric iron during the process of reduction and oxidation. In soils that have fluctuating wet and dry conditions, wide fluctuations in Eh occur. Micro site differences complicate these measurements in that anaerobes may be active and at 1‐cm away they are completely inactive. The ferrous–ferric iron couple usually dominates these measurements but other couple often contributes complicating the measurements and interpretations of the data. Reference electrodes are often fine for laboratory work but are not rugged enough for the field. In this chapter, suggestions for improvement are discussed. Field‐measuring equipment and the Pt electrode are also sensitive and subject to problems that often lead to spurious results in the field. These problems are discussed at length. Iron‐coated tubes and other methods of establishing redox conditions are relatively recent and are discussed, also.