Anaerobic digestion plants are increasing in Norway, and the Tingvoll farm biogas plant has been utilised for several R&D projects. Digested animal manure, household organic wastes or other organic materials is a fertiliser with high contents of mineral nitrogen. Such nitrogen is easily available for plant growth, but may also easily be emitted by application in field. Former studies have shown that addition of grounded marble to animal manure may reduce odour and N-emissions. The aim of MARMORFIKS (“Marble-fix”) is to study if grounded marble added to digested and non-digested slurry can increase the yields of grass-clover ley, as compared with digestate and non-digested slurry without marble addition.