Interaction of Nitrogen Availability During Bloom and Light Intensity During Veraison. I. Effects on Grapevine Growth, Fruit Development, and Ripening

A variety of environmental factors affects both vegetative and reproductive growth in grapevines. The effect of nitrogen (N) availability at bloom (0.34, 1.7, or 3.4 g N per plant as NH4NO3) and light intensity at veraison (three weeks at 100%, 20%, or 2% sunlight, using shade cloth) on growth and fruit ripening of pot-grown Cabernet Sauvignon (Vitis vinifera L.) vines were investigated. Low N supply during bloom reduced fruit set due to inflorescence necrosis. Both high N availability and low-light conditions stimulated shoot growth and leaf area expansion, and delayed leaf senescence, but decreased the weight of grape skins and the skin to berry ratio. Abundant N nutrition also reduced pulp sugar and acid levels by the beginning of the ripening period. However, the N induced differences became gradually smaller towards fruit maturity. Limited sunlight during veraison also delayed grape ripening, and this was exacerbated by high rates of applied N. Low light inhibited the degradation of malate during fruit maturation. However, ripening was not stopped entirely by light intensities as low as the light compensation point of photosynthesis. Upon restoring full sunlight the vines compensated partially for the previous photosynthate deficit by maintaining relatively high rates of sugar accumulation in the berries. Under full sunlight sugar accumulation reached a plateau five weeks after veraison. No relationship between crop yield and fruit quality could be established at harvest, although there was an almost sixfold range in yield. Yield was determined primarily by N availability at bloom, while grape quality was determined predominantly by light conditions during veraison.