Manganese occurs in practically all soils, but the quantities present are exceedingly variable. Twenty-six typical soils analyzed by Robinson showed the presence of manganese in amounts varying from 0.01 to 0.51 per cent of MnO. Other studies have shown the occurrence of very large amounts in certain soils, but the average of 0.071 per cent MnO given in the work referred to above probably represents fairly accurately the manganese content of normal soils in this country.
Brown, P. E. and Minges, G. A.
"The effect of some manganese salts on ammonification and nitrification,"
Research Bulletin (Iowa Agriculture and Home Economics Experiment Station): Vol. 3
, Article 1.
Available at: https://lib.dr.iastate.edu/researchbulletin/vol3/iss35/1