Nitrogen Fertilization of White Riesling in Washington: Effects on Petiole Nutrient Concentration, Yield, Yield Components, and Vegetative Growth

Nitrogen fertilizer was applied through the drip irrigation system to White Riesling (Vitis vinifera L.) grapevines at rates of either 0, 56, 112 or 224 kg N/ha per year for three years. Pruning weight increased up to 112 kg N/ ha and shoot weight tended to increase with increasing rate of N fertilization. The first year, fruit yield increased when N fertilizer was applied, but did not differ between 56 and 224 kg N/ha fertilized vines. Vines were pruned to equal node numbers the preceding winter. Vines were balance pruned the last two years. Fruit yield peaked at 56 kg N/ha in 1987 and 112 kg N/ha in 1988. When data were pooled over the three years, yield tended to increase with increasing bloomtime petiole NO3-N concentration to about 1500 mg/kg. Above 1500 mg/kg, yield was not correlated with bloomtime petiole NO3-N concentration. Based on yield and pruning weight, application of no more than 56 kg N/ha is recommended to White Riesling grapevines growing in soils low in N and under well-managed trickle irrigation.