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One-year-old `Concord' grapevines (Vitis labruscana Bailey) were fertigated with 0, 5, 10, 15, or 20 mm N in a modified Hoagland's solution for 8 weeks during summer. Half of the vines fertigated at each N concentration were sprayed with 3% foliar urea twice in late September while the rest served as controls. Four vines from each treatment combination were destructively sampled during dormancy to determine the levels and forms of N and carbohydrates. Nitrogen fertigation during the summer did not significantly alter vine N concentration whereas foliar urea application in the fall significantly increased vine N concentration. In response to foliar urea application, concentrations of both free amino acid-N and protein-N increased, but the ratio of protein-N to free amino acid-N decreased. Arginine was the most abundant amino acid in free amino acids and proteins, and its concentration was linearly correlated with vine N concentration. Concentrations of total nonstructural carbohydrates (TNC) decreased slightly in response to N supply from fertigation. Foliar urea application in the fall significantly decreased TNC concentration at each N fertigation level. Starch, glucose, and fructose decreased in response to foliar urea applications, but sucrose concentration remained unaffected. Approximately 60% of the carbon decrease in TNC caused by foliar urea application was recovered in proteins and free amino acids. We conclude that free amino acids account for a larger proportion of the N in vines sprayed with foliar urea compared with the unsprayed vines, but proteins remain as the main form of N storage. In response to foliar urea application, part of the carbon from TNC is incorporated into proteins and free amino acids, leading to a decrease in the carbon stored in TNC and an increase in the carbon stored in proteins and free amino acids.

One-year-old `Concord' grapevines (Vitis labruscana Bailey) were fertigated with 0, 5, 10, 15, or 20 mm nitrogen by using a modified Hoagland's solution for 8 weeks during active vine growth in summer. Half of the vines at each N concentration were sprayed with 3% foliar urea twice in late September while the rest served as controls. After natural leaf fall, all the vines were overwintered in a cold room (2 to 4 °C). Four vines from each treatment were destructively sampled before budbreak for reserve N and carbohydrate analysis. The remaining vines were supplied with either no N or sufficient N (10 mm N) from 2 weeks before bloom to 1 month after bloom. All the vines were destructively harvested at 1 month after bloom. Total amount of N in dormant vines increased with increasing N fertigation concentration. Total nonstructural carbohydrates (TNC) increased with increasing N fertigation concentration from 0 to 10 mm, and then leveled off with further rises in N supply. Foliar urea application increased total N but decreased TNC of dormant vines at each given N fertigation level. When no N was provided during the regrowth period, vine total leaf area, fruit yield, and total dry weight increased with increasing N supply from fertigation the previous year. Vines sprayed with foliar urea the previous fall produced a larger total leaf area, a higher yield, and a higher total vine dry weight at each given N fertigation concentration. Providing vines with sufficient N during the regrowth period significantly increased total leaf area, fruit yield, and vine total dry weight across the previous N fertigation concentrations, but vines sprayed with foliar urea still had a larger leaf area, a higher yield, and a higher total vine dry weight at each given N fertigation concentration. Therefore, we conclude that both vegetative growth and fruiting of young `Concord' vines are largely determined by reserve nitrogen, not by reserve carbohydrates, and that current-season N supply plays a very important role in sustaining vine growth and development, especially fruit growth.