Study finds vineyard leaves drain more nutrients than growers expect

A new study from Washington State University is urging grape growers to rethink how they calculate nutrient losses in vineyards, finding that a vine gives up important nutrients through far more than the grapes picked at harvest.

The research, published in the American Journal of Enology and Viticulture, examined how nutrients leave grapevines over the course of a season in irrigated vineyards in Eastern Washington. It found that while harvested fruit removes large amounts of potassium and nitrogen, other pathways, including leaf fall, winter cane removal and weather-related disruption, can also make a major difference in how much nutrition a vineyard loses in a given year.

For growers, that matters because fertilizer programs are often built around fruit removal. If other losses are underestimated, vines can enter the next season short of nutrients, which can affect growth, yield and fruit quality. If losses are overestimated, growers may apply more fertilizer than they need, increasing costs and environmental pressure.

“The study highlights the importance of taking a more holistic view of vineyard nutrient management,” Nataliya Shcherbatyuk, the lead author and a research associate in Washington State University’s Department of Horticulture, said in comments released with the study. She said growers usually account for nutrients removed by harvested fruit, but other pathways receive much less attention even though they may contribute meaningfully to annual losses.

The work is part of the USDA-funded High Resolution Vineyard Nutrient Management Project. Researchers analyzed nutrient loss data from Syrah, Sauvignon Blanc and Chardonnay wine grapes, along with Concord grapes grown for juice. All of the samples came from irrigated vineyard systems in Eastern Washington, one of the country’s most important grape-growing regions.

The scientists found that crop yield remains one of the strongest drivers of nutrient removal. In years or blocks where vines produce more fruit, more nutrients leave the vineyard with the harvested crop. But the study also found that leaves can carry away significant amounts of calcium and nitrogen, in some cases more than growers might expect.

That finding is important because many vineyard nutrient budgets focus heavily on the bins or trailers of fruit leaving the field and less on what happens after the canopy shuts down in the fall. Grapevines normally begin to move some nutrients out of aging leaves and back into permanent structures, including roots, before those leaves drop. Those stored nutrients then help support early growth the next season.

Markus Keller, the project director and Chateau Ste. Michelle Distinguished Professor in Washington State University’s Department of Viticulture and Enology, said that process can be interrupted by early frost. If leaves are killed before the vine finishes reclaiming nutrients from them, those nutrients are lost instead of being stored for spring growth.

“At the end of a growing season, the dying leaves will recycle nutrients back into the vine’s roots, where they are stored until the next season,” Keller said. “With an early frost, that doesn’t happen.”

He added that if early frosts happen routinely, vines can become nutrient deficient because those reserves are not available at bud break, forcing growers to make up the difference with fertilizer.

The study also points to a broader problem facing vineyards across the western United States: weather variability is making nutrient management harder to predict. Drought can reduce a vine’s ability to take up nutrients from the soil. Strong winds can blow leaves out of the vineyard, moving nutrients away from where they might otherwise decompose and return to the system. Warmer autumns can keep vines active later in the season, only for a sudden freeze to cut off nutrient recycling before it is complete.

Spring weather can create a different version of the same problem. Keller said warm conditions can trigger early bud break, but a later freeze can damage that new growth and force the vine to push out another round of shoots. That restart uses stored resources and can leave the plant nutritionally strained.

“Both situations are problematic, because you’re essentially running the vine out of nutrients,” Keller said.

Researchers said these swings in weather can also change canopy size, vine biomass and crop level, all of which affect how much nutrition is removed during the year. In practical terms, that means a fertilizer program that worked one season may be poorly matched to the next if it does not take changing conditions into account.

The findings come as growers face pressure to use water and fertilizer more efficiently. In many western vineyards, fertilizer is applied through drip irrigation, a practice known as fertigation. While common, many of those systems are not built for highly precise, vine-by-vine adjustments across blocks where soils, vigor and water status may vary.

Keller said many drip systems are difficult to customize for variable-rate nutrient applications in heterogeneous vineyards. To address that limitation, Washington State University researchers have partnered with Oregon State University scientists to install a prototype single-vine drip irrigation system at the university’s Prosser research vineyard. The device, developed by an Oregon State team led by Chad Higgins, is designed to allow more precise fertilizer delivery by accounting for variation within a vineyard rather than treating an entire block the same way.

Researchers involved in the project said the long-term goal is to give growers better tools for deciding not only how much fertilizer to apply, but when and where to apply it. The project has already produced tools such as leaf nutrient sensors and mapping systems intended to improve timing and reduce unnecessary inputs.

Shcherbatyuk said future work will look at nutrient losses across more grape varieties, vineyard sites, climates and management systems. That expanded research could be especially useful for an industry dealing with a wider range of weather extremes and trying to fine-tune input costs without weakening vine health.

Raj Khosla, dean of Washington State University’s College of Agricultural, Human and Natural Resource Sciences, said the work is aimed at helping growers manage vineyards more efficiently through applied research. For vineyard managers, the study adds a clear message: the nutrients leaving a vineyard are not limited to what goes into a winery truck or juice processor’s bin, and the growing season does not end nutritionally when the fruit is picked.