Earlier-flowering hairy vetch a great advance, but northern farmers need more
Winter survivability is the first consideration, and ‘Purple Bounty’ shows vulnerability.

By Dave Wilson, The Rodale Institute research agronomist

Posted April 12, 2007: Introduction of a new variety of hairy vetch featuring a bloom stage that is an estimated two weeks ahead of standard hairy vetch is great news in conventional seed selection—but it may not have the winter hardiness to make it a dependable choice for areas with winters at the colder end of the range typical in the northeastern United states.

That’s my honest assessment after examining plantings of ‘Purple Bounty’ in our fields in recent weeks. The fall-seeded plots established well, but low temperatures with stiff winds in a period of no snow cover created the kind of harsh conditions that make survival difficult for winter-annual leguminous plants. Farmers have a new-and-improved hairy vetch, but we’ll need more winters to really know how to rate its winter hardiness.

The ‘Purple Bounty’ introduction marks real progress in developing seed genetics specifically adapted to fit into complex rotations critical in organic systems and useful across all crop systems.

Cover crops are a key component of organic production systems. Organic growers are looking for cover-crop cultivars that perform well in diverse crop rotations and tillage regimes to improve soil fertility and enhance biodiversity. The Rodale Institute utilizes hairy vetch (vicia villosa, a winter annual legume cover crop) as a key component of our cropping systems. It serves as an excellent soil cover and source of nitrogen, especially in organic no-till corn production.

Since hairy vetch has the potential to biologically “fix” large quantities of nitrogen, we plant it in a rotation sequence before corn, which is one of our heaviest nitrogen-feeding crops. We use different management techniques to derive many benefits from hairy vetch, for both the soil and following crop. In some cases, we moldboard plow the hairy vetch cover crop to use it as a green manure for our corn crop. In other fields, we roll and crimp the hairy vetch when it is at full bloom to create the dead cover-crop mulch on the soil surface into which we no-till plant corn.

Earlier is better

In the latter case, we aim to grow hairy vetch varieties that bloom early so that we can roll and kill the cover crop as soon as possible for earlier no-till corn planting. In the Northeast, farmers must balance the desire for early corn planting with the need to let vetch grow to accumulate maximum nitrogen-rich biomass and reach full bloom. Mowing or rolling before full bloom results in poor kill of the vetch, often with re-growth.

Normally at our location, hairy vetch reaches full bloom in late May to early June—sometimes pushing corn planting to the first or second week of June—forcing us to look for shorter-season corn varieties for our no-till killed cover crop system. By selecting hairy vetch cultivars that reach full bloom earlier, we can roll-kill and plant earlier, gaining some growing degree-day heat units for the no-till corn and allowing us a broader choice of corn varieties.

In most of the upper midwestern and northeastern states, hairy vetch is more cold tolerant and vigorous than other winter annual legumes such as crimson clover. Hairy vetch is a top nitrogen producer and is widely adapted in these regions. However, some hairy vetch varieties are more susceptible to winter kill than others. Winter kill can severely reduce hairy vetch biomass production in the spring, which limits its nitrogen production and ground cover capacity for weed suppression.

Successful hairy vetch cultivars for the Upper Midwest and Northeast need to be:

  1. Winter hardy and resistant to winter kill.
  2. Early blooming to allow quicker peak N contribution and effective roll-down suppression.
  3. Vigorous enough to produce adequate amounts of biomass for weed suppression (at least 5,000 pounds of aboveground dry matter per acre, at standard row widths) and nitrogen delivery (at least 6,000 pounds of above-ground dry matter per acre). In both cases, more vetch is better, particularly to supply N.

In 2005, The Rodale Institute collaborated with research geneticist Thomas Devine, Ph.D., from the USDA-ARS Sustainable Agriculture Systems Laboratory in Beltsville, Maryland. He provided 14 different selections of hairy vetch to evaluate for winter survivability and date of bloom. We included six more commercially produced hairy vetch selections from different seed-tag origins.

We planted replicated plots of the different hairy vetch selections and evaluated them at various stages from emergence to roll-down. This trial was also replicated at the Pennsylvania State University and the Beltsville USDA-ARS site. Data on emergence date, percentage of ground cover, winter survivability, spring biomass, the progression of bloom by date, percent kill with rolling, percent re-growth and percent nitrogen in the tissue were collected at our location and used to assess the viability of each selection.

Breaking the early barrier

As a result of this coordinated effort, the USDA will release a ‘Purple Bounty’ later this year. It was not developed with the use of genetic engineering, so it is acceptable for seed-increase production programs that produce the seed for certified-organic growers. ‘Purple Bounty’ flowered two weeks earlier than most of the other selections evaluated, it produced adequate amounts of biomass to suppress weeds and supply adequate nitrogen, and it was announced as having sufficient winter hardiness to survive winters in the Northeastern United States

The USDA is currently preparing the "Notice of Release of ‘Purple Bounty’ Hairy Vetch," and the USDA-ARS Sustainable Agriculture Systems Laboratory, Animal and Natural Resources Institute, in Beltsville, Maryland, will maintain breeder’s seed for the new variety. The seeds will also be deposited in the National Plant Germplasm System where they will be available for research purposes, including the development and commercialization of new cultivars. However, because the cultivar is a new release, seed is not yet commercially produced or available in large quantities for farmers.

In the fall of 2006, another season of hairy vetch evaluations was started and is currently under way. Dr. Devine provided six selections for this evaluation. We are also analyzing commercial hairy vetch seed selections from different seed-tag origins (including Oregon, Minnesota and Nebraska), and seed from farmer Steve Groff of Lancaster County, Pennsylvania (who has been growing his own selection of an early cover hairy vetch).

When early is not enough

While ‘Purple Bounty’ survived the winter of 2005 with no problem (it performed well and bloomed two weeks earlier than most other varieties), it has not fared as well during the 2006-2007 winter at the Rodale location, averaging 96 percent aboveground kill in our trials (as evaluated on March 27). By comparison, the commercial seed selections with seed-tag origins from Nebraska and Minnesota in this 2006-2007 trial have 48-percent and 5-percent winter kill, respectively. Illustrating the seed-breeder’s challenge, both of these top winter-hardy varieties are late-blooming.

We do not yet know how well the ‘Purple Bounty’ plants will ultimately recover when warm weather comes to stay in southeastern Pennsylvania. In some years, hairy vetch re-grows adequately from its roots here and in others it doesn’t, depending on the extent of the kill and how much carbohydrate is stored in the plant’s roots to support new growth. We are observing some new shoot growth from the crowns of the new cultivar’s plants, and our evaluation will continue through the spring and early summer.

Although we are very enthusiastic about the success of the ‘Purple Bounty’ selection, winter survivability is a more critical factor than the early bloom in the most of the Northeast. Winters in Pennsylvania’s southernmost counties and locations south of the Mason-Dixon line are typically less severe, increasing the probability that ‘Purple Bounty’ will successfully overwinter. Farmers in these areas will probably benefit from its early bloom on a consistent basis. However, for farmers in more northerly regions where winter conditions are more unpredictable, the strain’s winter survivability may become less certain.

Subfreezing temperatures, in association with water in the soil, on the soil surface or in the plant itself can clearly cause serious hairy vetch stand losses. The winter kill of the aboveground portions of the ‘Purple Bounty’ vetch this past winter was attributed to periods of extremely low temperatures that coincided with little or no snow cover.

A little protection helps a lot

The crowns and roots of even the most cold-resistant legume cannot stand direct exposure to temperatures 15°F or below for very long without incurring injury or death. Therefore, insulation is critical to the survival of legumes in the colder regions. Coverings of snow or plant material (such as frost-killed oats or crop stubble) can often provide adequate protection from low temperatures.

We often plant hairy vetch with spring oats in late August or early September, allowing the spring oats to act as a protective cover when they are winter killed. Snow and vegetative cover (which can aid in accumulating additional snow) are very effective insulators of soil and plants due to the buffering air pockets they create.

In fact, a more cold-sensitive variety of hairy vetch will actually do well in a climate that is cold but provides enough precipitation to shelter it with a continuous blanket of snow. Given the variability of temperature and snow cover in some regions of Pennsylvania, the overwintering success of winter-hardy vetches such as ‘Purple Bounty’ is less predictable from year to year. In more southern mid-Atlantic areas, such as at Dr. Devine’s research station in Beltsville, it should thrive.

Because of the key importance of nitrogen fixation in hairy vetch used before corn, winter-kill resistance should be a primary selection factor before flowering earliness is considered. In the southern environments where winter kill is less of a concern, more emphasis can be given to early flowering date.

We have observed significant variability in these traits among different hairy vetch selections, so we feel progress is possible on both winter-kill resistance and early flowering if a multiple culling selection program with interbreeding is employed. Opportunities for this type of research exist and need to be supported.

Most commercially available hairy vetch seed is labeled simply as “hairy vetch,” sometimes noted as “VNS” (variety not stated). Cultivar variety names are typically not listed on the seed tag, so you have no ability to choose a specific cultivar selection.

For northern growers with unpredictable winters, we recommend planting hairy vetch seed that is locally grown or grown in an area north of your latitude to indicate sufficient winter survivability for your fields.