Manganese Oxides As an Indicator of Reduction in Soils (IRIS).

Over the last decade, IRIS (Indicator of Reduction in Soils) technology has been introduced and developed whereby Fe oxide paint is applied to PVC devices (usually tubing) and inserted into the soil. Under strongly reducing conditions during the oxidation of soil organic matter by heterotrophic microbes, Fe oxides on the tubes are utilized as an electron acceptor, and the oxidized Fe is reduced, solubilized and stripped from the device leaving white or lighter colored areas. The IRIS devices are easy to use and interpret and are less prone to difficulties associated with other methods of assessing reducing soil conditions, and have been endorsed by the National Technical Committee on Hydric Soils.  For many years there has been interest in the development of Mn oxide coated tubes (Stiles et al., 2010) but until recently there have been insurmountable problems associated with poor adhesion/durability of the Mn oxide coating on the PVC tubing.  Some workers have recently suggested that following the procedure of Handel et al.(2013), birnessite easily synthesized at room temperature, could be used to make Mn coated PVC IRIS devices, but it appears that there are significant difficulties associated with using birnessite synthesized according to these specifications. Although durable Mn-coated tubes can apparently be manufactured using specialized and time consuming procedures, when the Mn oxide suspension is painted onto the PVC devices in the manner normally used in making Fe coated tubes,  the Mn oxide coating does not adhere but rather rubs off easily.  Through recent advances, the author has been able to surmount these difficulties. This paper will report on the development of an easily synthesized Mn oxide paint that can be used to quickly make IRIS tubes with a strongly adhering and durable Mn oxide coating.