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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:
- Winter hardy and resistant to winter kill.
- Early blooming to allow quicker peak N contribution and
effective roll-down suppression.
- 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
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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. 
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