A SPECIAL GROWERS’ REPORT OF AG ALERT ® C A L I F O R N I A Trees & Vines ®
Farm advisors say nitrogen deficiency can limit berry size in table grape varieties, and applying too much nitrogen may delay maturity. But proper applications can enhance taste and appearance.
For grape growers, nitrogen can be an ally or enemy ByDennis Pollock Nitrogen can be a friend or foe to growers of wine or table grapes. Too much of it can delay maturity. Too little limits berry size and can affect berry chemistry and color.
in the vineyard after harvest. Nitrogen deficiency limits berry size and can also affect berry chemistry and color, Fidelibus said. Applying more nitrogen than is needed does not further improve fruit quality, he said, andmay delaymaturity. It can, however, increase berry size. Analysis of tissue samples is helpful for confirming vine nutrient status andmay help evaluate nitrogen fertilization programefficacy. Petioles are standard tissues, but some people prefer blades.Mineral content of plant tissues can change rapidly over the course of the season, Fidelibus said, especially around bloom. Standard sampling times are bloomand veraison. Inone study, itwas found that excessnitrogendelayedmaturity inaCrimsonvineyard. Fertilizingmade the fruit less red. Fidelibus said researchers areusingadroneandseeking tocomeupwith“smartmaps” that show likely levels of nitrogen, while sampling leaves to corroborate inferences. Postharvest isnot agood time toapplynitrogen, becausevines arenot activelygrowing, he said. Nitrogen in the leaves is being reallocated to other parts of the vine at that time. Vines should fill the trellis fully without excessive shading, Fidelibus said. Severely
Toomuchcanalso result inadense canopy that enhances diseasepressure and impair quality. Feeding grapes certain amounts of nitrogen at the right time—whether in the winery or the vineyard—can enhance the taste, appearance and other qualities of the finishedwine. Those are insights of Matthew Fidelibus, a University of California Cooperative Extension specialist in viticulture, and Tian Tian, a UCCE viticulture farm advisor in Kern County. At a recent UCDavis Viticulture and Enology Winter Grape Day, Fidelibus discussed vineyardmonitoring that includes tissue sampling. He described current research on Flame Seedless, a table grape variety on Freedom rootstock that showed very low petiole nitrate levels. Nitrates in the groundwater were low, and there was a sparse canopy. In most studies, the average was 3 pounds of nitrogen per ton of fruit harvested, Fidelibus said. The aimwas to replace the nitrogen in the fruit. Fruit uses 40% of nitro- gen that is accumulated, he said, and the rest is used in leaves and stems, which remain
See NITROGEN, Page 8
January 26, 2022 Ag Alert 7
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