Growth and fruiting of young 'Concord' grapevines in relation to reserve nitrogen and carbohydrates

Abstract

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 nrea 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.