The objective of the research is to enhance knowledge in the field of soil-plant relationships, in order to contribute to an optimal use of nutrients by plants. It will evaluate chemical and biological soil factors and their interaction in controlling the supply of a plant with nutrients. The emphasis of the studies will be on the individual plant root to filed scales. it will not oriented towards a specific agricultural system. This means that research questions are addressed, no matter whether the context is a conventional, organic, or tropical system. Also natural ecosystems can be taken into account, since knowledge from these systems can be of use in soil fertility research. The research focuses on questions related to 'excess' situations in which undesired emissions to the environment have to be reduced, to poorer situations in which nutrient availability is low. In all cases the research should contribute to an optimal nutrient use by plants.