Nitrogen (N) fertilization experiments were maintained for three growing seasons in commercial Cabernet Sauvignon (CS), on Vitis riparia rootstock, and Merlot (M), on SO4 rootstock, vineyards in British Columbia. Six treatments were applied annually in a randomized block design with eight replicates and 10 vines per experimental plot. Treatments included the standard commercial vineyard N application rate of 40 (M) or 45 (CS) kg N/ha or double these rates, applied either at budbreak or bloom. A split N treatment involved application of the low N rate at bloom, followed by the same amount applied immediately postharvest. An organic N treatment involved surface application at budbreak of compost estimated to supply the standard N application rate. For Merlot, petiole N concentration before and at bloom was highest each year after application of 80 kg N/ha at budbreak. In two years, delaying N application until bloom was associated with decreased canopy density and increased yield. Berry yeast-assimilable N concentration (YANC) exceeded deficiency only for the high N rate applied at bloom. Bloom-time N application for Merlot has promise as a strategy for targeting berry N status without causing excess vegetative growth. There were few differences in vine performance between those receiving N as compost rather than urea at budbreak. Postharvest N applications did not affect fruit composition or YANC. The Cabernet Sauvignon site had adequate YANC regardless of N treatments. Altering N rate and timing had few multiyear effects on canopy density, yield, and fruit composition. Applying budbreak N as compost rather than urea resulted in similar vine performance. The postharvest N treatment increased cumulative yield without adverse effects.
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