1. Adams, F. (1971). Ionic concentrations and activities in soil solutions. Soil Science Society of America Proceedings, 35, 420–426. Anderson.
2. Argersinger, W. J., Jr., Davidson, A. W., & Bonner, O. D. (1950). Thermodynamics and ion exchange phenomena. Transactions of the Kansas Academy of Science, 53, 404–410.
3. Beckett, P. H. T. (1971). Potassium potentials–A review. In Potash Review (pp. 1–41). Bern: International Potash Institute.
4. Beckett, P. H. T. (1972). Critical cation activity ratios. Advances in Agronomy, 24, 376–412.
5. Bertsch, P. M., & Thomas, G. W. (1985). Potassium status of temperate region soils. In R. D. Munson (Ed.), Potassium in Agriculture (pp. 131–162). Madison: Am. Soc. Agron.