NITROGEN DEFICIENCY/EXCESS
Nitrogen is necessary for many vine functions, including overall vine growth, fruit bud formation, fruit set and fruit size. Because of the complexity of nitrogen interactions with quality and production, the best guide for nitrogen requirements is leaf analysis.
Identification
Deficiency
- Low vine vigour
- Foliage turns pale green then yellow
- Young shoots, petioles, and cluster stems become pink or red
- Shoot growth is greatly reduced
- Sometimes light brown islands of dead tissue appear between the main veins of the basal leaves, and in extreme cases the leaf blades may wilt and abscise
- Berries may be small
- Winemakers may note low N levels in fruit at harvest for yeast available nitrogen (YAN)
Excess
- Internodes become long and large (bullwood)
- Excessive numbers of lateral shoots develop and grow excessively
- Oversized thick and sometimes cupped leaf blades with deep green colour
- Poor fruit set with excessive N levels during bloom period
- Delayed fruit maturity
- Poor wood maturation
Scouting Notes
Cool growing conditions in early spring often cause plants to exhibit a temporary nitrogen deficiency. This is usually due to poor growing conditions, and not necessarily a lack of nitrogen in the soil. Nitrogen deficiency often occurs when a permanent grass is seeded in the vineyard with low organic matter levels in the soil or when a large amount of organic matter which is low in nitrogen, such as straw, is worked in to the soil. The first symptoms may appear after berry veraison because nitrogen is translocated from the leaves near the clusters into the berries. Deficiency symptoms may also occur when fertilizer applied early in the year is leached by heavy rains or when it is not available for uptake due to extremely dry soil conditions.
Management Notes
Apply only the amount of nitrogen that is recommended based on petiole analysis done at veraison. Nitrogen applications should not be applied in advance of bud break or 2 weeks prior to bloom. Avoid late season nitrogen applications as this may delay vine maturity and increase risk of winter injury.
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