Delvaux, B., Dufey, J., Vielvoye, L., & Herbillon, AJ. (1989). Potassium Exchange Behavior in a Weathering Sequence of Volcanic Ash Soils. Soil Science Society of America Journal, 53(6), 1679-1684. https://doi.org/10.2136/sssaj1989.03615995005300060011x (Original work published 1989)