Introduction: Iron is one of the most important micronutrients for its role in the formation of chlorophyll and in various enzymatic processes. Though iron is present in most soils in sufficient quantities, it is not always available to plants, because it is bound to, or incorporated in soil particles. When plants suffer from an iron shortage, they will display deficiency symptoms and crop yields can be strongly depressed. To overcome this problem in agricultural practice, iron chelates are being applied. Chelates are "multidentate complexing agents" (ligands with more than one functional group). These iron chelates keep iron in the soil solution, so that plants can take it up. Agricultural practice has shown excellent results on the application of these iron chelates, and several different mixtures of iron chelates are being sold on the market. However, the understanding of the mechanisms underlying the behaviour of these iron complexes in the soil and the eventual uptake of iron by the plants is limited. This understanding is crucial for improving iron chelate products and applying the chelates in a way that gives optimal crop yields. Aim: Within the PhD project different aspects can be studied by MSc students, like: - To examine which chelate structure is optimal for supplying iron to the crop - To compare the crop response to iron supply for different types of plants - To gain a better understanding of how soil properties determine the effectiveness of chelates in delivering iron to the plant and to come to recommendations on how Fe supply could be improved with respect to the soil conditions. Outline: The project will consist of an initial literature study, to become acquainted with the subject. The main part of the study will be a series of plant experiments in pot trials and in nutrient solutions, with different iron chelates, different plants and different soils. The study will be concluded with an interpretation of the data (possibly with some modeling) and a written report on the experimental research.