The use of catch crops is an agro-environmental whose purpose is to reduce the losses of nitrogen after a certain cultivation (in this case, cereal crops) as compared to a crop which is not followed by a vangewas. Upon administration of a supplementary fertilization on the cereal stubble so it should be so that the N-leaching losses are smaller than with a (unfertilised) cereal stubble which is not followed by a catch crop. In addition, the losses should not be significantly greater than at a cereal stubble followed by a non-fertilized catch crop. The research question from VLM is initially or fertilizer on cereal stubble followed by a catch crop, is possible within these constraints, and how great fertilizer than can be. Since these fertilization on the stubble is not currently understood, it is necessary to carry out an overall assessment of the fertilizing norm in the total fertilization standard for the cereal. Additionally, it must be determined what the effects of the insertion of the catch crop, with additional fertilization, in the build-up of organic (carbon) of the substance in the soil. Within the increasingly stringent fertilization in Flanders is the preservation or the build-up of soil organic matter (BOS), after all, a very big concern. The aim of the research project is to give a reasoned answer to these questions through a combination of literature review, previous field trial data, targeted field tests, incubation and modeling within a strict time frame. An explicit goal is so set up the experiments and model simulations which is published (at least part of) the results in international peer-reviewed journals available by the end of 2013. The review of this research in international scientific expert knowledge through such publications will all one of the strongest arguments to convince the EC DG Environment of the soundness of the conducted research. Optionally consortium members the results of this study it will defend at the DG Environment; at such time, the scientific expertise of the consortium can be decisive.