Chapter 16

Vineyard Nutrient Management

Macronutrients and Micronutrients

Potassium

Role and Deficiency Symptoms

Vines need potassium for the formation of sugars and starches, for the synthesis of proteins, and for cell division. Potassium also neutralizes organic acids, regulates the activity of other mineral nutrients in vines, activates certain enzymes, and helps to adjust water relationships. It is also involved in cold hardiness, and the formation of carbohydrates, even though it is not usually found as part of organic compounds.

Potassium deficiency usually appears early- to in mid-summer starting with a color loss at the leaf edges. As fading continues, it moves into the areas between the main veins, gradually decreasing as it approaches vein areas in the center of the leaf. Symptoms are likely to occur at véraison and to continue through ripening since the demand for potassium is highest during fruit ripening in mid- to late summer.

Assessing the Need for Potassium Fertilizer

As with most other macronutrients, tissue sampling can be used to determine the vines’ potassium status.

Time of Application

Potassium fertilization via banding or broadcasting it is best applied in late fall or early winter. Rain can move it into the rootzone making it available for uptake during the growing season.

Application Methods

Direct Soil Surface Application: Dry potassium fertilizers (e.g., KSO4) are applied directly to the soil surface either as broadcast or banding. Broadcasting potassium fertilizers over the entire vineyard is less efficient and less economical. If banded, the potassium 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: Potassium applied by drip irrigation offers better control of application. However, it may be difficult to limit the application to the deficient areas of the vineyard.

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

Soil Factors Affecting Availability

In alkaline soils, increased levels of other cations such as calcium, magnesium and sodium can affect the availability of potassium. The calcium and magnesium cations can displace the potassium from the exchange sites on the clay particles and sodium competes with potassium for uptake by the vine root system.

Potassium Toxicity

Extremely high potassium levels may induce a magnesium deficiency. It is important to note that excess potassium in fruit will raise the pH in the wine and lower its acidity, which affects taste and wine stability.

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