Effect of Nitrogen on Growth and Composition of Fruits from ‘Thompson Seedless’ Grapevines1

Growth, yield, and composition of ‘Thompson Seedless’ fruits from 4-year-old vines growing in a perlite-vermiculite mixture and irrigated with half-strength Hoagland nutrient solution modified to contain 0, 1/2, 1, 2, 4, or 8 mM NO 3 were studied. Vines grown without N added to tap water produced no fruits. Number of clusters per vine and number of berries per cluster were significantly less for vines grown with 1/2 or 8 mM NO 3 than for vines which received 1, 2, or 4 mM NO 3 . Weight, pH, and malate level of berries increased with increasing levels of NO 3 in the nutrient solution. The concn of arginine in berry juice increased linearly with increasing levels of NO 3 from 1/2 through 4 mM, and then remained relatively constant, with about a 12-fold increase between the lowest and highest NO 3 treatments. A second-degree quadratic equation best described this relationship with a correlation coefficient of 0.95. The level of proline, however, continued to increase between 1/2 and 8 mM NO 3 with about a 4-fold overall increase. The concn of proline in the juice of grapes at harvest was much more sensitive to level of ripeness (°Brix) than to N treatment, whereas the opposite relationship was true for arginine. The arginine levels in fruits grown with 1/2 to 8 mM NO 3 increased 9 to 20-fold when compared at the same stage of ripeness (°Brix). Total soluble solids, total acidity, and tartrate in berries were not significantly affected by N treatment.