Gray comes from precipitate of MnO 2 on outside of root. In waterlogged soil, usually see reduction after a number of days of anaerobiosis. After C source is utilized, insoluble manganic compounds are reformed. B. Iron 1. Iron, a minor nutrient for plants, is often unavailable for uptake and deficiencies are common.
Microbial role is very important.
Under alkaline to neutral conditions, ferrous iron is unstable in presence of oxygen and is oxidized abiotically. Microorganisms can't compete. Oxidation occurs as a result of different types of microbial activities. Shows characteristics of growth. Organism often becomes coated with ferric hydroxide generated abiotically during process.