NITROGEN-FERTILIZATION OF WHITE RIESLING GRAPES IN WASHINGTON - MUST AND WINE COMPOSITION

Nitrogen (N) fertilizer was applied to White Riesling grapevines through the drip irrigation system at rates of 0, 56, 112, or 224 kg N/ha for three years. Attainment of 21% soluble solids was delayed as rate of N fertilization increased. Juice and wine titratable acid and organic acid concentrations did not vary due to N fertilization rate. Juice pH increased linearly with increasing N fertilizer rate and was related to juice titratable acid and ammonia concentration. Juice potassium concentrations were not affected by N fertilizer rate, while wine potassium concentrations increased linearly with increasing N. Wine pH increased with N fertilizer rate and was related to tartrate and to a lesser extent to potassium concentration. Juice total N, ammonia, free amino nitrogen, arginine, and proline concentrations increased linearly with increasing N fertilizer rate. Wine urea concentrations after four to six years of storage at 15-degrees-C was low (highest concentration was less than 10 mg/L), but increased linearly with increasing rate of N fertilization.