It's not easy to figure out exactly where all that topsoil is going, or what's tagging along with it — let alone how to stop it. But it's a challenge the California Central Coast Vineyard Team (CCVT) is tackling in its ongoing effort to help wine grape growers promote sustainability in the vineyards, reduce potential negative environmental impacts from commercial growing operations, and comply with federal and state regulations.

“We have several ongoing projects right now that address critical issues in our industry, such as erosion, water quality and pesticide mitigation,” says Jill Whitacre, CCVT program director for the Paso Robles-based organization. “We have growers and university cooperators who work very closely with us to conduct field trials, collect data and help find solutions to these challenges we all face.”

One of those growers is Mitch Wyss, vineyard manager for Halter Ranch Vineyard, west of Paso Robles. “The work that the vineyard team does helps keep us viable as farmers,” he says. “As a grower participating in these projects, I learn as much about what doesn't work as what will work.”

Evaluating cover crops and their efficiency at reducing erosion and pesticide/fertilizer runoff is the focus of one of the field trials currently being conducted on Halter Ranch. The trial started with cover crop plantings in late November 2005. The picturesque site is an ideal setup for the trial with south facing vine plantings on steep terrain. The vineyard's proximity to nearby creeks and rivers that drain into lakes and the Pacific Ocean is a concern due to the potential for erosion. It's typical of many vineyards in the area in terms of topography and environmental issues.

“We get rainfall events that can trigger sediment movement into creeks that ultimately drain into Lake Naciemento,” Wyss says. “We don't want to lose that soil anymore than someone wants to see it go into a creek, or wind up in a lake, or anywhere else offsite.”

The cover crop and runoff study at Halter Ranch is a three-year program funded by the Regional Water Quality Control Board. The study is designed to help growers adopt Best Management Practices (BMPs) for their vineyards so that they can comply with the Conditional Ag Waiver.

“The use of cover crops is one of the most effective ways to reduce runoff and minimize the offsite movement of pesticides, fertilizers and sediment,” Whitacre says. “The idea is to get rain drops to hit leaves instead of the soil. If a rain drop hits the soil first, there is a lot more risk for that soil to move and take anything that might be in it along with it.”

The cover crop trial that is still ongoing at Halter Ranch includes 20 different species that range from vetches to clover to barley to wildflowers and many others. To get an idea of how the cover crops perform, dry matter production and percent cover are measured each year. Clippings that are taken from a 2-by-4 quadrant — bagged, dried, and weighed — measure dry matter production of each species.

In 2006, the cover crops that showed the most promise included: purple vetch, common vetch, Austrian pea, crimson clover, barley UC603, clover mix, and wildflower mix.

Unfortunately, the past two years of the study have been anything but typical as far as weather is concerned. In 2006, it snowed twice at Halter Ranch during the winter, and then heat spikes in February of that year enabled weeds to get a head start on some of the late germinating species.

This past winter was unusually dry, which thwarted another effort to determine runoff measurements. San Luis Obispo County University of California Cooperative Extension Farm Advisor Mark Battany designed and constructed devices that measure rainfall runoff on the slopes of the vineyard.

“In a normal year, the west side of Paso Robles gets about 30 inches of rain,” Whitacre says. “This past winter it only got about 10 inches. There basically wasn't any runoff to measure due to the drought.”

In spite of the atypical years thus far, the effort continues. Costs of the various cover crops are also factored into the analysis. In 2007, the costs of cover crop seed varied from $0.19 per pound for an annual grass (Hordeum vulgare), to $34.00 per pound for a perennial grass (Melica Californica). Some cover crops in the trial are native to the region while others are introduced. Some of the cover crops were planted at two different rates.

The most expensive seed — Melica Californica — planted at a rate of 40 pounds per acre cost $1,360.00 per acre, while the least expensive seed ran $9.50 to $15.20 per acre, depending on the seeding rate. A detailed breakdown of the costs can be found on the CCVT website at: www.vineyardteam.org.

While some cover crops have performed better than others, the jury is still out regarding long-term performance.

“I'm glad to be involved in the study,” Wyss says. “It's part of being a good neighbor and a responsible grower. Right now, we're producing 6,000 cases of wine, but we have plans to increase that to about 25,000 cases. The vineyard itself is capable of producing about 60,000 cases. We have plans to expand the winery and tasting room as well.”

Halter Ranch currently grows about 20 wine grape varieties, which are mostly comprised of reds — nearly halved between Bordeaux and Rhone styles. Although most of the vineyard is under drip irrigation, Wyss is also experimenting with some acreage that is dry farmed.

Expansion at the vineyard calls for innovative solutions to minimize environmental impact and comply with the multitude of federal and state regulations. “I believe the research projects that CCVT oversees and runs helps us tremendously as growers,” Wyss says. “I don't mind supporting them one bit, because they support us.”