Uptake, Storage, and Utilization of Soil-applied Nitrogen by Thompson Seedless as Affected by Time of Application

A grapevine9s need for nitrogen (N) is most critical during the period of rapid shoot growth in spring through bloom and early berry development. Timing of fertilizer applied to the soil necessary to maximize nitrogen in leaf tissue during this period was evaluated in two mature Thompson Seedless vineyards. Application periods, using labeled ammonium sulfate, included budbreak, July, and post harvest in late September. Application in July and September resulted in the highest content of labeled nitrogen in dormant storage tissue, and in leaf tissue during rapid spring growth and at bloom. It is apparent that labeled nitrogen stored in roots, trunk, and canes during dormancy was redistributed to support early spring growth. Nitrogen applied at budbreak had insufficient time for uptake to become a significant fraction of total N in leaf tissue by bloom.