Together with the disappearance of oxygen and nitrate, an increase in the manganous ion (Mn ++) in the soil solution and on the cation exchange complex is one of the first measurable effects of ...

Williams, R. J. P., in “The Enzymes”, edit Boyer, P. D., Lardy, H., and Myrbäck, K., 1, chapter 9, p. 391 (Academic Press, New York, 1959).