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Cover crops can do more than fight weeds and improve the health of vineyard soils.

Growers in California are finding the right crop can also help reduce erosion, prevent leaching of nitrogen and phosphorus, and boost the environmental quotient of vineyards.

That was the message farm advisor Larry Bettiga of the University of California delivered to growers during a session focusing on sustainable grape growing at the annual viticulture and enology conference hosted by the British Columbia Wine Grape Council in Penticton, Canada, last summer.

The current goals of cover crops include controlling weeds, reducing the impact of farming on natural waterways and the loss of soils from vineyard sites, as well as promoting favorable and efficient growing circumstances, Bettiga said.

Some of the factors affecting the kind of cover crop selected include soil characteristics, which influence both what can grow and how permeable the floor is to rain. A cover crop should match both local growing conditions and, if desired to reduce erosion, should reflect the volume of rainfall at the site. California views cover cropping differently than areas with higher levels of precipitation, Bettiga noted.

There may be local environmental pressures, too. Some municipalities will require that vineyards have management programs in place to manage runoff, or require growers to submit plans regarding the mitigation of a farm’s environmental impacts. The benefits of cover crops include the creation of habitat for beneficial insects and nematodes, the retention of nutrients, and some nitrogen fixing.

"We know that with persistent cover cropping we can build up the organic matter in the soil. With that, we see some additional benefits of soil tilth, better percolation of water through the profile, and we have documented greater microbial activity where those cover crops are grown," Bettiga said.

Competition

On the other hand, a cover crop may also attract pests (such as gophers and other vertebrates), and there may be impacts on the vines due to competition for nutrients.

"We do know that from previous studies, vines when they’re very young are very prone to competition, more so than a mature vineyard, but also, in some areas, even mature vineyards can be excessively out-competed by a very aggressive cover," Bettiga said.

Bettiga uses ryes and fescues in his area, and advises changing the cover crop occasionally to prevent weeds from exploiting weaknesses in the cropping system. Weeds will not only defeat part of the purpose of having a cover crop, but will boost the cost of the program because manual weeding will be required to eliminate the interlopers.

Bettiga’s research showed that cover cropping actually had very little benefit on the soils in which the vines themselves were grown, however.

In-row cover?

He therefore launched a project to determine if inrow cover crops—usually frowned upon—could deliver benefits.

"In many of our publications, we recommend against it, because if it’s not done correctly, it can have some negative implications with vine vigor and vine yields," Bettiga said.

But there are benefits. A plot with in-row barley plantings saw less erosion and an increase in microbial activity, for example. While there was a reduction in shoot growth from the in-row cover crops, Bettiga believes close management may reduce those impacts.

Indeed, sound vineyard management is as much part of managing cover crops as cover crops can be part of a vineyard management strategy by itself. The management of cover crops is especially important because they’re typically a cost rather than a source of revenue.

"You really have to be careful with what you’re doing and what your goals are. And again, they need to be developed based on the characteristics of the site and what your budget projections are and how much money you’d like to spend on some of these things," Bettiga said. "There’s always an economic consequence of whatever you do in the vineyard." 

Sustainable practices committee formed

With sustainable grape-growing programs enjoying healthy support elsewhere in North America, British Columbia growers are taking a look at the concept for the Okanagan Valley.

The B.C. Wine Grape Council established a sustainable practices committee in early 2008 to explore the potential of establishing a program to certify vineyards that practice sustainable viticulture.

"A lot of people tend to look at California and everywhere else and say, ‘What are we doing? They’re doing this, we should get on the bandwagon,’" said Dr. Tom Lowery, a research scientist at the Pacific Agri-Food Research Centre in Summerland and one of three speakers on a panel regarding sustainable viticulture at the B.C. Wine Grape Council’s annual viticulture and enology conference in Penticton last summer.

Lowery remarked that despite the trendy character of all things sustainable, most B.C. growers practice low-impact viticulture and would likely meet whatever standard any program mandates.

But Lowery warned growers that consumers want to know that growers’ commitment to sustainable practices is genuine. Certification is a good way to prove sincerity, he said.

A timeline for developing a program has not been set. —P. Mitham