Evening Primrose and Rapeseed Yield Components and Grain Oil Concentrations Were Differentially Modulated by the N, P, and K Supplies in a Mediterranean Area

Evening Primrose (Oenothera biennis L.) is an industrial crop-producing seed with high oil concentration characterized by high gamma-linoleic acid. However, limited information is available on its response to the nutrient supply, especially P and K. The aim of this work was to compare the response of Evening Primrose to the application of N, P, and K alone or in combination in a P and K deficient soil in terms of grain yield, yield components, and oil composition in comparison to Rapeseed (Brassica napus L.). Evening Primrose yielded 54.4% less seed and 67.3% less oil than Rapeseed. Such differences were reduced when nutrients, especially N or P, were applied. N stimulated Evening Primrose more than Rapeseed. Application of K favored Evening Primrose oil yield when no N or P were added, and this especially occurred by an enhancement of the pod number. P favored yield per pod and oil yield in the Evening Primrose more than Rapeseed in almost all conditions. Fertilization scarcely affected lipid composition. In particular, an increase in the oleic acid concentration was found only when N + K or N + P + K were applied compared to the sole N or sole K applications. These results suggest that P and K differentially influenced yield components of both species and that Evening Primrose was less adapted than Rapeseed to a scarce nutrient supply.