Alison Reeve, Patricia Skinkis,* and R. Paul Schreiner
*Oregon State University, 4017 Ag & Life Sci Bldg, Corvallis, OR 97331 (patricia.skinkis@oregonstate.edu)

Pinot noir has lower yield potential than many winegrape cultivars and annual yield variation is considerable in the cool climate of western Oregon. Climate and nutrient status may influence yield, but information on their physiological impacts on yield predictors such as fruitfulness is lacking. High vegetative vigor and shading have been related to poor bud fruitfulness; many vineyards in the region are characterized by high vegetative growth that requires canopy management to ensure adequate light infiltration. A long-term vineyard floor management trial was established to alter Pinot noir vine vigor using perennial grass cover (Grass), tillage (Tilled), or a combination of both (Alternate) in alleys flanking vine rows. Yield and vine size were altered by years four to six. It was hypothesized that lower yields were a result of both low vine nitrogen (N) and carbohydrate reserves by way of reduced bud fruitfulness. During years seven through nine, the trial was used to determine whether vine N and carbohydrate status influenced the presence of floral primordia in buds, fruitfulness, and yield at harvest. Grass vines had reduced veraison leaf area, pruning weight, and yields compared to Tilled vines, and the effect was likely due to the lower N status of Grass vines. Yield reduction was due to reduced fruitfulness that related to low vine N status, rather than to the vine total non-structural carbohydrate status (TNC). Grass vines had 0.2 fewer inflorescences per bud than Tilled, which reduced yield by ~43% in two of three years. Although Grass vines had higher canopy light infiltration than Tilled, buds were less fruitful. This study suggests that vine N status of both annual tissues and reserves is a more important determinant of yield capacity than light exposure, photoassimilation, and TNC status.

Funding Support: Oregon Wine Board Agriculture Research Foundation