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°C was low (highest concentration was less than 10 mg/L), but increased linearly with increasing rate of N fertilization.