Every autumn, grape growers in Eastern Washington watch their vines shed leaves that should be quietly recycling nutrients back into the roots for winter storage. But as weather patterns shift, that natural process is breaking down, and a new study from Washington State University shows just how much this matters for grape production.Researchers found that vineyards lose nutrients not just through the harvested fruit people buy at the store, but also through leaf fall, dormant cane removal and extreme weather events. In some cases, nutrient losses through leaves were much larger than many growers might expect.
The study, published in the American Journal of Enology and Viticulture, analyzed nutrient loss in four grape varieties: Syrah, Sauvignon blanc, Chardonnay and Concord juice grapes, all grown in irrigated vineyards across Eastern Washington. The scientists discovered that while potassium and nitrogen leave the vineyard mainly through harvested grapes, leaf fall accounts for a significant portion of calcium and nitrogen losses.
Lead author Nataliya Shcherbatyuk, a research associate in WSU's Department of Horticulture, said the findings could help growers develop more accurate fertilizer budgets. "While growers routinely account for nutrients removed through harvested fruit, there are other pathways that receive much less attention despite their potential contribution to annual nutrient losses," she said.
Markus Keller, the project director and Chateau Ste. Michelle Distinguished Professor in WSU's Department of Viticulture and Enology, explained why weather is making nutrient management harder. Normally, dying leaves recycle nutrients back into the vine's roots where they are stored until spring. But increasingly, warmer falls keep plants active longer, only for an early frost to strike before that process finishes. "If early frosts occur on a routine basis, the plants will eventually become nutrient deficient because those nutrients aren't available at bud break the following season," Keller said. Growers must then compensate by adding more fertilizer.
Strong winds can also carry grape leaves out of the vineyard entirely, making their nutrients inaccessible. Drought conditions reduce a vine's ability to absorb nutrients in the first place.
The research is part of WSU's High Resolution Vineyard Nutrient Management Project, which has already produced practical tools like leaf nutrient sensors and maps to help growers improve efficiency. Scientists have also partnered with Oregon State University to test a new single-vine drip irrigation system at the WSU Prosser research vineyard, developed by an OSU team led by Chad Higgins. The prototype could allow for more precise fertilizer application tailored to each vine's needs.
"Our scientists are working on important research that directly affects the health of vineyards, allowing grape growers to manage their vineyards as efficiently as possible," said Raj Khosla, dean of WSU's College of Agricultural, Human, and Natural Resource Sciences. The research team plans to continue studying nutrient loss across different grape varieties, climates and vineyard conditions.