Fruit & Vegetable Magazine

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Keeping vines healthy through good nutrition


November 6, 2012
By Dan Woolley

Topics
Dr. Kevin Ker

There is such a problem as too much of a good thing. And Dr. Kevin Ker has seen it with the overuse of fertilizer in vineyards.

“If you don’t need extra nutrients; why pay for them?” he asked those attending the Atlantic Canada Wine Symposium held recently in Halifax, N.S.

The critical elements required for grapevine development are nitrogen, phosphorus, potassium, calcium and sulphur, explained Dr. Ker, an independent vineyard consultant and research associate at the Cool Climate Oenology and Viticulture Institute (CCOVI) at Brock University in St. Catharines, Ont. Other required micronutrients include boron, copper, zinc and chlorine.

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Critical nutrients
Problems in a grape can be aggravated by over-applying nitrogen, said Dr. Ker. Nitrogen stimulates plant growth, which is linked to excess flowering on the vine. As a result, nitrogen applied during the blooming period will result in poor fruit set.

“I never apply all my nitrogen in the spring,” he said, adding that growers really shouldn’t apply any nitrogen within four weeks of bloom.

“You don’t need to apply nitrogen before bud break,” Dr. Ker said.

Once leaves appear on the grapevines, their roots start taking up nutrients from the soil.

Phosphorus is involved in root production and has a role in disease control in vines, he explained.

“Be aware of this so you don’t over-apply phosphorus as a nutrient.”

Potassium is involved in the active transportation of nutrients into the grapevine’s cell structure, said Dr. Ker. He warned that “a little is good” but too much potassium can create problems for the winemaker because the sugar levels in the grapes will be unstable.

Calcium makes the grape skins harder and Dr. Ker recommends it be applied as a foliar spray application against the Botrytis spore. Growers should also consider applying calcium during periods of drought or when calcium levels are low, he added. It costs about $8 to $10 per acre to apply and Dr. Ker suggested it be combined when growers are spraying pesticides or herbicides.

Manganese contributes to fruit quality and too much calcium or potassium can displace manganese, he said.

Sulphur is necessary for protein building and also plays a role in growth regulation and plant hormone production, said Dr. Ker. It is also a key nutrient for seed production.

“No seeds, no berries,” he said.

Sulphur is also a component of chlorophyll and sulphur deficiency makes fruit set difficult and will lead to “fruit shatter,” said Dr. Ker.

Micronutrients
Boron has a role in germination, fruit set and shoot development and, if it is deficient, will affect root growth, he said. The micronutrient is typically applied as a foliar application beside the row as a low-cost stimulant for vine roots, Dr. Ker advised.

If zinc is deficient, he urges growers to apply it but understand high application rates will likely not help cold tolerance in the vines.

Dr. Ker recommends growers apply nutrients below the canopy drip line as 95 per cent of nutrient uptake occurs in this narrow zone. He added that the uptake of nutrients by the vines occurs within the top 18 inches of the soil.

Growers should establish their vineyards’ base level nutrient requirements to help diagnose problem areas, and the nutrient levels should be monitored over time, advised Dr. Ker. Site-specific soil tests can tell growers the nutrient levels in the soil. Samples should be taken beneath the vines on each side of the row about 18 inches out with at least 10 to 15 soil core samples along each row. Each core sample should be between eight and 12 inches in depth.

He recommends removing surface debris before taking a core sample or it’s possible the vegetation will bias the results.
Dr. Ker added that growers should try to take core samples at the same time each year.

“If you do it in September, it is the time when decisions on vineyard management should be made,” he said.

Soil structure is another important component of grapevine health and vineyards should be monitored for soil compaction as it can cause productivity problems, said Dr. Ker, adding that growers may want to consider sub-soiling regularly to maintain good soil structure.

“Organic matter is one of your best friends,” he said.

As a result, growers should try to maintain a soil profile of between two and four per cent organic matter, said Dr. Ker, adding that a light, sandy soil will need more frequent organic matter applications.

“Grapevines really don’t need or want much nutrient,” he said. “They like a little bit of water but they don’t swim.”

Tissue samples can also tell a grower if nutrients are reaching the grapevine’s cellular structure. Dr. Ker said tissue samples can provide information on the nutrient concentrations in the vine’s tissues. The results will be variable with the tissue sample collected and the time of the growing season when collected, he said, adding that the nitrogen content in tissues can also fluctuate over the season, depending on the stresses being experienced by the vines.