Short flax fibers are by-products that have no current used yet. An interesting idea is to convert them as a fully biodegrable nitrogen source possible to spread in the crop fields. Indeed, intensive agricultural production requires currently nitrogen fertilizers but it induces soil and groundwater pollution. However, this system can offer the benefit to gradually release the nitrogen in the soil thereby avoiding any form of pollution.For this purpose, a protocol was developed to attach casein hydrolysate (peptides, nitrogen source) on flax fibers yarns using chitosan. A cellulose coating was then added to contain and to allow a progressive release of the casein hydrolysate. Firstly, the cellulose coating stability and its compatibility with the initial casein hydrolysate attachment was demonstrated. Secondly, through an enzymatic model, it was confirmed that natural degradation will lead to casein hydrolysate release into the soil. Therefore, this study demonstrates the short flax fibers yarns functionalization interest to obtain a new eco-friendly nitrogen source, i.e. a non-polluting fertilizer for crop fields.