Viticulture – Improved Understanding of Grapevine Nutrients and their Management Session

Partitioning of Foliar and Fruit-Applied Nitrogen in Grapevines

Pierre Davadant,* Nataliya Shcherbatyuk, Juliana Pazos, Lee A Kalcsits, James F Harbertson, and Markus Keller

*University of Tennessee, 2431 Joe Johnson drive, 301 Agriculture and Natural resources building, Knoxville, TN, 37996, pierre.davadant@utk.edu

Grapegrowers in dry regions face challenges with low nitrogen (N) in harvested grapes, affecting winemaking due to insufficient yeast assimilable nitrogen (YAN). Foliar N application at veraison may enhance grape and wine composition without inducing excessive vigor, yet its effect on phenolic compounds and plant N partitioning remains unclear. We conducted a 3-yr field trial and two separate pot experiments in arid eastern Washington to test whether foliar-applied N moves to the fruit and other plant organs, enhancing berry ripening and quality, and potentially replenishing the available N pool to support next year’s crop. In a field trial with own-rooted Syrah, we applied liquid urea ammonium nitrate (0, 22.5, 45, 90 kg N/ha) to the soil at bloom or foliar urea (15 kg N/ha) at veraison. We also tested the impact of supplementing a foliar urea spray at veraison (20 g N/L) on potted Cabernet Sauvignon vines that had received four different rates of soil N at bloom (0 to 3.75 g N per pot). Finally, using potted Riesling vines, we applied ¹⁵N-labelled urea at veraison on whole canopies, leaves only, or clusters only to trace N partitioning. Results showed that foliar N application at veraison significantly increased YAN in field-grown Syrah and potted Cabernet Sauvignon, especially in low-N vines. Higher YAN in Cabernet Sauvignon berries at harvest was negatively correlated with skin tannins, but not seed tannins. ¹⁵N applied on Riesling fruit remained in the clusters, while ¹⁵N applied on leaves was translocated to both the clusters and the perennial plant organs for storage. Pot experiments showed that foliar N also effectively enhanced vine growth in the following year.

Funding Support: USDA-NIFA Specialty Crop Research Initiative (award number 2020-51181-32159), Washington State Grape and Wine Research Program, Ste. Michelle Wine Estates (in-kind)

Nitrogen Management in the Mid-Atlantic: Insights from Four Fertilization Field Experiments in Virginia

Andrew Harner,* Amanda Stewart, Dana Acimovic, Megan Mershon, Marlon Ac Pangan, Valeria Araujo, and Tony Wolf

*Virginia Polytechnic Institute and State University, 595 Laurel Grove Rd, AHS Jr. AREC, Winchester, VA, 22602, dharner@vt.edu

Nitrogen (N) is essential for vine growth and grape production. In the cellar, fruit N contributes to fermentation and wine sensory characteristics. Achieving optimal vine N status in Mid-Atlantic vineyards can be challenging, as heterogenous soils and variable environmental conditions interact to mediate soil N availability. High seasonal precipitation can promote supraoptimal N availability and excessive vegetative growth, while periods of drought may reduce N absorption. To investigate how N fertilization affects grape production, vine growth, and fruit composition, and how environmental conditions mediate these relationships, we conducted four field experiments in Virginia Chardonnay and Chardonel vineyards as part of an SCRI-funded initiative. We tested three rates of soil-based calcium nitrate applications (0 kg/ha; 33 kg/ha, applied at full bloom; 65 kg/ha, split into applications at full bloom and 4 wk after) and two rates of foliar urea applications (0 kg/ha; 5.7 kg/ha) at veraison. We sampled petioles and leaf blades to determine nutrient status at key phenological stages, harvest yield parameters, chlorophyll content index, juice maturity traits, juice amino acid composition at harvest, and pruning weights. We hypothesized that soil amendments would be more effective at improving vine N status than foliar fertilizers, with all amendments increasing fruit N. The following themes emerged: soil applications elicited the greatest overall plant response, although differences were subtle between moderate and high rates of soil fertilization; foliar applications only consistently affected chlorophyll content and fruit N pools at harvest; leaf blades were optimal for detecting changes in vine N status; vine size was greater following soil applications in seasons with ample precipitation; and fruit N pools were sensitive to all applications. These results emphasize the role of environmental conditions in mediating N uptake and can be used to inform N management strategies in vineyards experiencing variable seasonal conditions.

Funding Support: USDA NIFA SCRI CAP Award Number #2020-51181-32159, Virginia Wine Board, Virginia Agricultural Council, and Virginia Tech College of Agriculture and Life Science

Grace E. Lilly | Patricia A. Skinkis*

Vine Nitrogen Dynamics: Rootstocks Alter Pinot noir Growth and Productivity More than Yeast Assimilable Nitrogen

Grace E. Lilly and Patricia A. Skinkis*

*Oregon State University, Department of Horticulture, Oregon Wine Research Institute, 2750 SW Campus Way, 4017 Ag & Life Sciences Bldg., Corvallis, OR, 97331, patricia.skinkis@oregonstate.edu

Nitrogen (N) is one of the most important macronutrients in grapevines that affects vine growth, productivity, and fermentation kinetics. Tissue N and yeast assimilable N (YAN) are indicators of vine and must N status used by grapegrowers and winemakers and can be influenced by rootstock. The most common rootstocks planted in Oregon are 3309C, 101-14, and Riparia Gloire, all vigor-reducing rootstocks that may limit N uptake and must N. A mature trial (27- to 28-yr-old) of Pinot noir grafted to eight rootstocks (1103P, 101-14, 3309C, 420A, 44-53, 5BB, Riparia Gloire, and Schwarzmann) and own-rooted vines was evaluated over 2 yr (2024 and 2025) to understand N dynamics under the non-fertilized, non-irrigated management common in Oregon’s Willamette Valley. There were differences by rootstock for vegetative growth, yield, vine and must N, and N utilization efficiency. Vines on 5BB, 420A, and 1103P were consistently high performers. These rootstocks had nearly two-fold vegetative growth and yield compared to vines on 3309C, 44-53, Riparia Gloire, and Schwarzmann (low performers). Vines on 5BB consistently had the highest N concentration in leaf blades at veraison. However, N utilization efficiency (yield/plant N) was consistently highest in the three high-performer rootstocks (1103P, 5BB and 420A). However, only 5BB had higher must YAN than all other rootstocks and own-rooted vines. While rootstock influenced vegetative and reproductive growth, the ratio of vine size-to-crop weight was also affected by rootstock. The high-performer vines on 5BB, 420A, and 1103P were balanced (yield: pruning wt: 7 to 9) while lower-performing vines on Riparia Gloire, 44-53, and Schwarzmann produced a higher proportion of yield relative to smaller canopies (yield: pruning wt: 12 to 15) and had lower N utilization efficiency. While rootstock can have a major impact on vine growth, yield, and N utilization efficiency, there is similar must N accumulation for Pinot noir.

Funding Support: Oregon Wine Board, Oregon Wine Research Institute

Navneet Kaur* | Geraldine Diverres | Markus Keller

Water, Not Nitrogen, is the Main Driving Force for Vine Growth and Yield

Navneet Kaur,* Geraldine Diverres, and Markus Keller

*Washington State University, 24106 N Bunn Rd, Prosser, WA, 99350, navneet.kaur6@wsu.edu

Vine vigor across a vineyard varies due to many factors such as soil water availability, elevation, or proximity to subsurface water. Vines with greater vigor will demand more plant nutrients, especially nitrogen (N). Contrarily, vigor can be controlled by limiting the N supply. In view of this, Riesling vines exhibiting different levels of vigor (high and low) due to differences in subsurface water availability were fertilized with two rates of N (high = 34 kg/ha, and low = 0 kg/ha) in the WSU Roza vineyard in the arid Yakima Valley of Washington, and data were collected from 2023 to 2025. Nutrient composition was determined in leaf tissues (blades and petioles) at veraison and berries at harvest. Yield components and pruning weights varied strongly by vigor class (i.e., water supply) while N application had no significant impact. High vigor vines produced 11% more and 24% heavier clusters, resulting in 36% higher yield, than low vigor vines. Similarly, canopies of high-vigor vines were 117% bigger than low-vigor vines. The berries from the high-vigor vines were more acidic and accumulated less total soluble solids. Additionally, the clusters from high-vigor vines were prone to sour rot infection. Like yield components, nutrient composition in leaf tissue and berries was mainly affected by vigor, but yeast assimilable nitrogen (YAN) was affected by both vigor and N application. High-vigor vines with higher N fertilization had 104% more YAN than low-vigor vines with low N across the three years. N application had a more prominent effect on YAN in the later years, suggesting that fertilizer effects can take time to appear. These results indicate that water availability has a greater effect on the growth and yield of grapevines than N availability.

Funding Support: USDA/WSDA Specialty Crop Block Grant Program (grant number K3944), Washington State Grape and Wine Research Program.

1:30 pm – 1:50 pm	Partitioning of Foliar and Fruit-applied Nitrogen in Grapevines Pierre Davadant, University of Tennessee, Knoxville
1:50 pm – 2:10 pm	Nitrogen Management in the Mid-Atlantic: Insights from Four Fertilization Field Experiments in Virginia Andrew Harner, Virginia Polytechnic Institute and State University, Winchester
2:10 pm – 2:30 pm	Water, not Nitrogen, is the Main Driving Force for Vine Growth and Yield Navneet Kaur, Washington State University, Prosser

Viticulture – Improved Understanding of Grapevine Nutrients and their Management Session

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