Many of your questions, as well as alternative spring management options for
vetch and other cover crops, are addressed in great detail in the SAN
publication: Managing Cover Crops Profitably, 2nd Edition. 1998. At the
risk of taking information out of context, I will include a section of the
chapter on killing vetch, below. Other parts of the same chapter would also
be relevant, including specifics on N contribution by the legume, mixing
with grain crops, weed control and moisture relations in no-till vs.
conventional till systems.
Excerpts from the book, including the complete chapter on cereal rye, are
available on the web at http://www.sare.org/htdocs/pubs/
The book also has a whole chapter on soil fertility (and health), including
discussions of soil microbes, tillage effects, nutrient cycling, estimating
N contribution from your cover crops. Other sidebars describe in detail
farmers' management of cover crops. We also made every attempt to suggest
management precautions, including the problems associated with too much
biomass production.
See http://www.sare.org/mccp2/orderpub.htm to order the $19 book--and
what a deal for 212 pages loaded with info just like the excerpt below!
Excerpt from Managing Cover Crops Profitably, 2nd Edition, chapter on hairy
vetch.
Copyright 1998 by the Sustainable Agriculture Network.
____________________________________________________________________________
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NOTE: numbers in parentheses refer to the bibliography, also on the web for
those who care to dig deeper.
Killing
Your mode of killing hairy vetch and managing residue will depend on which
of its benefits are most important to you. Incorporation of hairy vetch
vegetation favors first-year N contribution, but takes significant energy
and labor. Keeping vetch residue on the surface favors weed suppression,
moisture retention, and insect habitat, but may reduce N contribution.
In spring, hairy vetch continues to add N through its "seed set" stage after
blooming. Biomass and N increase until maturity, giving either greater
benefit or a dilemma, depending on your ability to deal with vines that
become more sprawling and matted as they mature.
Climate influences the results of hairy vetch residue management. In the hot
and humid conditions of the Southeast, no-till hairy vetch residue appears
to contribute significant N without incorporation. Findings elsewhere (272)
indicate that farmers in the cooler and drier areas of the western Corn Belt
need to manage hairy vetch with mowing and tillage to achieve peak N
benefits by preventing N volatilization (loss into the atmosphere).
Mulch-retaining options include strip-tilling or strip chemical desiccation
(leaving vetch untreated between the strips), mechanical killing (rotary
mowing, flailing, cutting, sub-soil shearing with an undercutter, or
chopping/flattening with a rolling stalk chopper) or broadcast herbicide
application.
No-till corn into killed vetch. The best time for no-till corn planting into
hairy vetch varies with local rainfall patterns, soil type, desired N
contribution, season length and vetch maturity.
In southern Illinois, hairy vetch no-tilled into fescue provided 40 to 180
lb. N/A over 15 years for one researcher/farmer. He used herbicide to kill
the vetch about two weeks before the area's traditional mid-May corn
planting date. The 14-day interval was critical to rid the field of prairie
voles, present due to the field's thick fescue thatch.
He kills the vetch when it is in its pre-bloom or bloom stage, nearing its
peak N-accumulation capacity. Further delay would risk loss of soil moisture
in the dry period customary there in early June (267). When the no-tilled
vetch was left to grow one season until seed set, it produced 6 tons of dry
matter and contributed a potentially polluting 385 lb. N/A (348). This high
dose of N must be managed carefully during the next year to prevent leaching
or surface runoff of nitrates.
A series of trials in Maryland showed a different mix of conditions. Corn
planting in mid-April is common there, but early killing of vetch to plant
corn then had the surprising effect of decreasing soil moisture and corn
yield, as well as predictably lowering N contribution. The earlier-planted
corn had less moisture-conserving residue. Late April or early May kill
dates, with corn no-tilled 10 days later, consistently resulted in higher
corn yields than earlier kill dates (62, 63, 64). With hairy vetch and a
vetch/rye mixture, summer soil water conservation by the cover crop residue
had a greater impact than spring moisture depletion by the growing cover
crop in determining corn yield (64).
Results in the same trials, which also included a pure rye cover,
demonstrated the management flexibility of a legume/grain mix. Early killed
rye protects the soil as it conserves water and N, while vetch killed late
can meet a large part of the N requirement for corn. The vetch/rye mixture
can conserve N and soil moisture while fixing N for the subsequent crop. The
vetch and vetch/rye mixture accumulated N at 130 to 180 lb./A. The mixture
contained as much N--or more--than vetch alone (63).
In an Ohio trial, corn no-tilled into hairy vetch at mid-bloom in May
received better early season weed control from vetch mulch than corn seeded
into vetch killed earlier. The late planting date decreased yield, however
(145, 289), requiring calculation to determine if lower costs for tillage,
weed control, and N outweigh the yield loss. Once vetch starts to bloom, it
is easily killed by any mechanical treatment (52).
To mow-kill for mulch, rye grown with hairy vetch improves cutting by
holding the vetch off the ground to allow more complete severing of stems
from roots. Rye also increases the density of residue covering the vetch
stubble to prevent regrowth.
Much quicker and more energy-efficient than mowing is use of a modified
Buffalo rolling stalk chopper, an implement designed to shatter standing
corn stubble. The chopper's rolling blades break over, crimp and cut crop
stems at ground level, and handle thick residue of hairy vetch or foxtail
millet at 8 to 10 mph (131).
No-till vegetable transplanting. Vetch that is suppressed or killed without
disturbing the soil maintains moisture well for transplanted vegetables.
No-till innovator Steve Groff of Lancaster County, Pa., uses the rolling
stalk chopper to create a killed organic mulch. His favorite mix is 25 lb.
hairy vetch, 30 lb. rye and 10 lb. crimson clover/A (132).
No-till, delayed kill. Jeff Moyer of the Rodale Institute in Kutztown, Pa.,
no-tills corn into standing hairy vetch in late May or early June, waits
several more days, then flail-chops the vetch before corn emergence. This
method allows the vetch to produce maximum N and is late enough to allow
soil warming even with the vetch in place (230).
Also useful in killing hairy vetch on raised beds as used in vegetables and
cotton is the improved prototype of an undercutter that leaves severed
residue virtually undisturbed on the surface (70). The undercutter tool
includes a flat roller attachment, which, by itself, usually provides only
partial suppression unless used after flowering.
Herbicides used to kill hairy vetch include glyphosate (only somewhat
effective), paraquat, 2,4-D, dicamba and triazines including atrazine,
cyanazine and metribuzin. Vetch will die in three to 30 days (338),
depending on the material used and crop conditions.
Vetch incorporation. As a rule, to gauge the optimum hairy vetch kill date,
credit vetch with adding two to three pounds of N per acre per sunny day
after full spring growth begins. Usually, N contribution by early bloom
(10-25 percent) stage warrants killing the legume, rather than accepting
yield loss due to late planting to get marginally more N at seed set or
natural dry down after seed set.
Cutting hairy vetch close to the ground at full bloom stage usually will
kill it. However, waiting this long means it will have maximum top growth,
and the tangled mass of mature vetch can overwhelm many smaller mowers or
disks. Flail mowing before tillage helps, but that is a time- and
horsepower-intensive process. Sickle-bar mowers should only be used when the
vetch is well supported by a cereal companion crop and the material is dry
(351).
Heavy disk harrows, rotovators and power spaders can incorporate heavy,
unmowed vetch stands. A moldboard plow can turn under large amounts of mowed
vetch. Chisel plows and lighter disks can handle vetch killed earlier with
herbicides.
_________________________________________________________________
End of excerpt from Managing Cover Crops Profitably, 2nd Edition, chapter on
hairy vetch.
Andy
Andy Clark, Ph.D.
SAN Coordinator
c/o AFSIC, Room 304
National Agricultural Library
10301 Baltimore Ave.
Beltsville, MD 20705-2351
PH: 301-504-6425
FAX: 301-504-6409
san@nal.usda.gov
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