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
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
Successful hairy vetch cultivars for the Upper Midwest and Northeast
need to be:
- Winter hardy and resistant to winter kill.
- Early blooming to allow quicker peak N contribution and effective
- 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
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
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