In oil palm, a similar fertilisation regime can result in leaflet potassium and magnesium concentrations that vary significantly from one progeny to another. This hinders the development of standardised fertiliser recommendations for this crop, as they are usually calculated to reach optimum leaflet nutrient concentrations. We tested the hypothesis that optimum leaflet K and Mg concentrations significantly differ between different oil palm progenies. Four high-yielding oil palm progenies with contrasting leaflet K and Mg concentrations (C1, C2, and C3 of Deli × La Mé origin and C4 of Deli × Yangambi origin) were treated with combinations of three levels of KCl and MgSO4, in a completely randomised split-plot factorial design with six replicates, where progenies were a sub-factor. For a given level of KCl or MgSO4, different leaflet K and Mg concentrations were found between progenies (