Potassium is the main nutrient in oil palm nutrition. On oil palm estates, potassium fertilization is usually adjusted based on leaflet K content. However, in the Magdalena river valley in Colombia where the soils are deficient in Cl, KCl has always caused a drop in leaflet K content, sometimes to deficiency levels, yet yields remain high. To elucidate this paradox, we conducted a multi-annual trial on 11-year-old oil palms by comparing unfertilized plots and plots receiving KCl or NaCl. We analysed the physico-chemical characteristics of the soils and the K, Ca, Mg, Na, and Cl contents of different organs: leaflets, rachises, petioles, stems, roots, and fresh fruit bunches. Our results showed that Cl stimulated the uptake of K, Ca, and Mg cations in aerial parts and that K was primarily stored in the stem (72% of the K in aerial vegetative organs). Our results also showed that the soils were rich in K easily accessible to the crop, a fact that conventional extraction of exchangeable cations did not reveal, and that the richness was probably of volcanic origin. Lastly, analysis of rachis K content was seen to be a good potential indicator of K taken up by the plant, and could thus replace leaflets for monitoring potassium fertilization in oil palm plantations.