Erviö, Raimo, and Osmo Mäkitie. 1969. “Studies on the Effect of Clay and Organic Matter Contents on the Determination of Cation Exchange Properties in Clay Soils by the Ammonium Acetate and Methylene-Blue Methods”. Agricultural and Food Science 41 (2):73-81. https://doi.org/10.23986/afsci.71727.