By: Cheryl Gray
Knowing how to protect a vineyard from the havoc wreaked by unknown threats is an important part of any grape grower’s toolkit.
One of those tools is a cover crop. Many experts agree that cover crops play a vital role in guarding vineyards because they have a major impact on vine health and the ecosystem that surrounds vineyards.
According to researchers at Texas A&M University, growing a cover crop can help reduce the use of chemicals that can adversely affect the environment. Cover crops can also reduce the physical toll on a vineyard that comes with frequent use of heavy equipment on the precious vineyard soil upon which grape plants depend.
Scientists at Oregon State University cite three main goals of what cover crops should accomplish when it comes to managing vineyard floors between the vines, in the headlands, around vineyard blocks and in the vine rows. Those goals are weed control, soil conservation and managing soil water. Vineyard design, age of the vines, soil type and grape-growing region all contribute to the process.
By definition, cover crops are any plants grown in vineyard middles and sometimes under vines. They are non-cash crops and are not harvested. Generally, cover crops are planted each year in the fall and spring. They are maintained on a perennial basis. Scientists advise that using cover crops requires a thoughtful approach to reap the benefits of this organic tool.
According to the United States Department of Agriculture, many types of cover crops are recommended specifically for vineyards. These recommendations come on the heels of field studies compiled by the USDA and its research partners.
The list includes grasses and cereals, such as barley, annual rye grass, winter cereal rye and winter wheat. The choices for cover crops also include legumes, such as fava beans, garbanzo beans, crimson clover, hairy vetch and Austrian winter pea. There are also brassicas and cruciferous vegetables that include mustard, rape, forage radish and oilseed radish.
Annual plants are the most frequent pick for vineyards. A major reason annual plants are chosen over perennials is to allow the cover crops an opportunity to grow and to provide seasonal soil conservation during winter. In the summer, the cover crop is tilled over, another benefit to the vineyard soil.
Cover crops are rated according to their ability to provide either slow or fast carbon. How they produce nitrogen is also key. Cover crops that are rich in substances such as cellulose and lignin are defined as so-called slow carbon sources. Fast carbon options include grasses and brassicas that contain easily biodegradable sugars. Legumes are cover crops that provide a good source of nitrogen.
Agriculture experts recommend using a cover crop strategy that creates a balanced mix of slow and fast carbon-producing plants and those that generate nitrogen. In this way, microorganisms can successfully degrade organic matter without choking off vital nitrogen that vineyard soil needs. The so-called “combo” meal of legume and grass provides the ideal blend because the two complement each other, providing fibrous and tsp root systems while also kicking in nitrogen for the vines. However, in cases where a single plant species has a proven track record, experts say go with it, but keep in mind that single species plantings need to be rotated in order to fight potential buildup of insects, bacteria, viruses, fungi and other pathogens that can harm vineyard plants.
There are other benefits to using cover crops. In addition to improving soil structure, they also help with water infiltration with their roots. Some of those roots can loosen soil up to five feet, reducing soil compaction and improving the penetration of water and air. Cover crops improve mineral fertility by helping the soil to better retain important minerals that vineyard plants need, including acting as a guard against minerals leaching. Cover crops can store vital minerals during winter months. They also provide aesthetic value to vineyards and traction for equipment and workers.
Another benefit that cover crops provide is that as they grow, they work to improve the biological activity and organic matter in vineyard soil. Once their leaves and other plant materials begin to decompose, they kick-start the benefits of this organic process by boosting organic matter within the vineyard soil.
Erosion and runoff are enemies of vineyards. Cover crops combat these problems by preventing the damage that rain can cause when it dislodges soil. They help block the growth of weeds by preventing them from germinating in the first place. They also provide a welcome habitat for vineyard-friendly insects and predators.
Nematodes are also harmful to vineyards. Among the worst of these parasites are root-knot nematodes that stay in one place on the plant and lesion nematodes that travel around. Cover crops can help curb some of this threat.
Cover crops also influence the growth of grapevines by forcing them to compete for water and nutrients in the soil. The additional nitrogen provided by cover crops also promotes the growth process.
Managing cover crops is a process that begins with making sure that the soil is properly cultivated for good germination. Many growers opt for using a shallow tiller to get the job done. Moistening and leveling the soil follows. Then comes the seeding, which is done according to the climate of each grape-growing region. Experts say that a no-till drilling method for seeding cover crops helps conserve the texture of the soil, provides uniformity in placing seeds and helps better establish the cover crop in the vineyard. After seeding, the seed bed soil should be lightly packed with proper irrigation setup to promote germination and establish the cover crop.
Cover crops need to be fertilized. Grasses and brassicas might need additional nitrogen for optimal growth. However, experts warn that this is where caution should be exercised because legume and grass mixtures promote increased nitrogen, which could result in too much nitrogen, resulting in too much of a good thing. Soil tests will likely be required to check the impact of any cover crops in play.
While the benefits are many, there are drawbacks to using cover crops. Their presence may increase water use, create a frost hazard and may result in competition with the vineyard plants for soil moisture and vital nutrients. Pest problems can also result when a cover crop isn’t kept at a reasonable height. Finally, there is the chance that the use of cover crops might result increased management and cost.
To combat the frost issue, many growers opt to mow down their cover crops in early spring, essentially using what is left for frost protection. Those cover crops are then allowed to pick up growth again before finally going to seed. Once the seed matures, the cover crop is mowed and either left on the surface or mixed into the soil with a shallow tiller.
There is a wide range of research available documenting the results of cover crop use throughout the grape-growing regions of the United States and beyond. In addition to the USDA, many colleges and universities with curriculums that focus on viticulture have useful resources for grape growers in their regional areas. Much of the research is performed in the field through partnerships with vineyards that not only want information but are willing to share it for the benefit of other grape growers who want to know more about the pros and cons of cover crops.
