Nitrogen effects on yield and canopy of ‘White muscat'

Nitrogen was spread as ammonium sulphate in a single application each spring for 3 years at 4 N rates: 0, 40, 80 and 160 kg/ha. Weed development increased since the first application but chopping of cover crop was effective. In trated plots, in June of the third year the botanical composition was shifted from clover to grasses. Botrytis damaged more severely grapes fertilised with 160 kg/ha than with 0 or 40 since the first year of fertilisation. Differences in grapevine yield and vigour appeared small and not significant for the two first years. In the third year canopy differences were evident at the highest N rates making a continuous wall, more open at the top, with larger and greener leaves than at 0 and 40 kg/ha. Net photosynthesis was lower at the lowest N rates than at 80 and 160 kg/ha according to changes in substomatal C dioxide concentration, without significant changes in stomatal copnductance.