Small plastic cage sleeves were used to protect the native seedlings from herbivores like rabbits.
Eastern Washington vineyards, with their scant rainfall and location in a high desert, are harsh environments for cover crops. It’s a challenge to get cover crops established and keep them alive when most vineyards use drip irrigation. But what if plants native to the area—and that fix nitrogen—could be used?
That’s what Benton City grape grower Jim Holmes of The Ancora Estates on Red Mountain wants to find out. He’s funding research to see if nitrogen-fixing native species can be established in his vineyards, naturally adding nutrients back to the soil.
Holmes has tried growing wheatgrass, fescue, and other cover crops in the past, most of which didn’t work but were also competing with the vines for nutrients. “The grasses take nitrogen out of the soil. I’m trying to find a way to add nitrogen back in a more natural way,” he said.
With the trend in the wine industry toward doing things in a more sustainable manner, some growers are adding compost or green manures instead of synthetic fertilizers, Holmes explained. “But when you do that—adding organic matter and such—you are changing the character of the vineyard. It might make it better, but it will take away from the natural desert terroir. I don’t want to change my vineyard floor, but I do need to fertilize it because every time a truck hauls away harvested fruit, I’m removing nitrogen and other nutrients from the vines.”
Legumes like clovers and vetches are often grown as cover crops in vineyards to refill the nutrient reservoir, he noted, but it’s always done in wetter climates. “For us, bringing the desert back into the vineyard is a better solution.”
Dr. Steven Link, former Washington State University Extension ecologist who is conducting the research, was introduced to Red Mountain several years ago when plans were being developed to transform large tracts of Washington State Department of Natural Resources land into commercial vineyards and wineries. Link, from nearby West Richland, was approached by several companies interested in using native plant species in winery landscaping.
Xeriscaping—landscaping with plants that consume little water— is an efficient way to landscape, especially when you’re located in the high desert. “Native species don’t require anything,” Link stressed. “There’s no need for water, fertilizer, and little time is required for management.”
Additionally, flowering species can attract beneficial predators, native plants help add biodiversity to the vineyard, and water conservation is a good message for winery visitors.
Previous eastern Washington cover crop research in wine grapes by Dr. Mercy Olmstead found that native species germinated poorly compared to commercially available species. Olmstead’s research suggested that the poor germination may have been associated with seeding depth and timing.
The research project began in June 2008 with Link collecting seeds of native species growing in the Red Mountain area. Link identified plants growing in similar soils to the Ciel du Cheval Vineyard where the trial would be planted. The vineyard has both sandy loam and silty loam soils. Surface soils were also collected under parent plant canopies to inoculate germinated seedlings with species-specific nitrogen-fixing bacteria before planting in pots.
Nitrogen-fixing native species used in Ciel du Cheval Vineyard trial
|Species||Common name||Growth form|
|Astragalus caricinus||buckwheat milkvetch||perennial forb|
|Astragalus caricinus||woodypod milkvetch||perennial forb|
|Astragalus succumbens||columbine milkvetch||perennial forb|
|Psoralidium lanceolatum||lemon scurfpea||perennial forb|
|Purshia tridentate||antelope bitterbrush||shrub|
|Lupinus sericeus||silky lupine||perennial forb|
Six native species were grown in a greenhouse during the winter, with seedlings planted in replicated plots in the vineyard row middles during March and April, 2009. To help with establishment, plants were drip irrigated once shortly after planting by moving the drip line from the vines to the plants, although Link said that planting seeds instead of seedlings should eliminate the need for irrigation.Observations were made last June to count the number of live plants and the number of plants flowering, and to categorize plants as either rapid growing or slow growing.
During a recent spring visit to observe winter survival of the six species in the trial, Link was pleased with the outcome. “Bitterbrush appears to have done relatively well,” he said, adding that the shrub likes windswept areas. Astragalus caricinus (buckwheat milkvetch) did well, along with A. succumbens, known commonly as Columbine milkvetch, particularly in the sandier soil. He rated the lupine species as “okay” because some looked dark green and thriving, but others were pale gray in color, which may mean that they weren’t associated with the right rhizobium bacteria.
“The whole objective is to narrow down the list of potential species and focus on what ones work best,” Link said.
Holmes is encouraged by the results. “We have some idea of what looks good, and we’ll now move to the seed stage, getting or collecting seeds and planting them in a seedbed as a nursery so we can grow more seeds.”
The second phase of the research is to conduct a seeding trial of the plants that did well. Planting seeds is a cheaper way to put in a cover crop than planting seedling plugs by hand, said Link. Plugs might work for small-scale vineyards, but would probably be too expensive for large commercial operations. “Once you get the native plants going, their root system will reach the drip line under the vine rows and you shouldn’t need to water them.”
Once plants are established, he will compare growth and yield of vines planted with the nitrogen-fixing species and control vines (those without cover crop) to determine how much nitrogen is being added to the soil.
Holmes thinks the project will require many years. Already, he has committed $16,000 to fund the research, but he’s prepared to spend many times that to see it through the final stage of having established, native shrubs and forbs growing in the middle of his vineyard rows.