Chapter 16

Vineyard Nutrient Management

Macronutrients and Micronutrients

Phosphorous

Role and Deficiency Symptoms

Phosphorus is essential for the general health and vigor of all plants. It is an important component of cell-membrane lipids, nucleic acids, energy carriers such as ATP, and some proteins. It is also required for sugar metabolism.

Vines are rarely deficient in phosphorous. If deficient in phosphorous it is often manifested late in the growing season as yellowing of interveinal areas of older leaves. The mature leaves develop characteristic symptoms, which include yellow patches between the veins on white fruited varieties and red patches between the veins on red fruited varieties (See Figure 16.3).

Assessing the Need for Phosphorous Fertilizer

As with most other macronutrients, tissue sampling can be used to determine the vines’ phosphorous status. Tissue analysis results (Table 16.3) coupled with visual observations should indicate whether to apply phosphorous.

Time of Application

Phosphorus via banding or broadcasting is best applied in the fall or spring to take advantage of any rain to move it into the root zone.

Application Methods

Direct Soil Surface Application: Dry phosphorus fertilizers are applied directly to the soil surface either as broadcast or banding. If banded, the phosphorous fertilizer should be applied in a 3 to 5 feet (0.9 to 1.5 m) wide band, parallel to the row. Take care to keep the band 18 to 24 inches (46 to 61 cm) away from the base of the vines.

Fertigation: Fertigation offers better control in the application of phosphorus. Fertilizer is normally applied during the middle of an irrigation set to allow pre-wetting of the soil. If the concentration of calcium and magnesium is high in the irrigation water, they will combine with phosphorus to form the solid compounds of calcium phosphate and magnesium phosphate.

Foliar Application: The use of foliar spray with macronutrients has limited benefits when compared to micronutrients.

Soil Factors Affecting Availability

Phosphorus is relatively immobile in most soils except for sandy soils. Phosphorus can be “fixed” in acidic soils with high iron and aluminum content to form insoluble compounds that are unavailable to the grapevine.

Phosphorous Toxicity

Excess phosphorus can induce potassium deficiency as well as a micronutrient deficiency, with iron, and zinc first affected.

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