Alfalfa remobilises the N reserves accumulated in the roots for regrowth after harvest in greenhouse conditions. This effect was studied in field conditions in order to know if 50 kg per ha of supplementary nitrogen fertilisation after each harvest could avoid removing N reserves in the roots or increase the shooting after cutting. Results showed an increase of dry matter yield (18.7 per cent) and crude protein content (11.3 per cent) in the whole plant due to N fertilisation, but no differences (P more than 0.05) were observed in shooting after cutting. Dry matter yield and crude protein content in the roots decreased in N non-fertilised plants.