Vineyard Nutrient Management
Essential Plant Nutrients
Zinc
Role and Deficiency Symptoms
Zinc is critical for auxin formation, for the elongation of internodes and in the formation of chloroplasts and starch. In grapes, zinc is essential for normal leaf development, shoot elongation, pollen development, and the set of fully developed berries.
The symptoms usually appear in early summer, at about the time when secondary shoot growth starts. Zinc is not very mobile within the vine, so if the nutrient becomes deficient, younger rather than older vine tissues will show symptoms.
Assesing the Need for a Zinc Fertilizer
As with most micronutrients, tissue sampling can be used to determine the vines’ zinc status. Tissue analysis results (Table 16.3) coupled with visual observations should indicate whether to apply zinc.
Time of Application
Zinc fertilizer can be applied late winter to early spring for soil surface applications. If zinc fertilizer is applied via drip irrigation it should be completed two or three weeks prior to bloom. This allows enough time for vine uptake by bloom.
Application Methods
Direct Soil Surface Application: Soil surface applications of zinc are not very effective because the tendency toward soil fixation necessitates the use of very high fertilizer rates in most soils, and cover crops will intercept a significant portion of the application.
Fertigation: Drip irrigation is effective but comparatively high zinc rates are still required and treatment may not last longer than a year.
Foliar Application: Except in severe cases, repeated foliar spray treatment is probably the most economical way to correct most zinc deficiencies.
Soil Factors Affecting Availability
Zinc deficiency is common on many soil types including calcareous, heavy clay, alluvial, sandy soils and peats. It is especially common on soils low in organic matter and of high pH. Availability of zinc may be reduced by water logging and where root growth is restricted.
Zinc Toxicity
Symptoms are rare, and most likely are masked by secondary symptoms resembling those of other micronutrient toxicities.
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