Hairy Vetch for Cover Cropping in Organic Farming

Organic Agriculture August 19, 2013|Print

Source:

Adapted from: Clark, A. (ed.) 2007. Managing cover crops profitably. 3rd ed. National SARE Outreach Handbook Series Book 9. National Agricultural Laboratory, Beltsville, MD. (Available online at: http://www.sare.org/publications/covercrops.htm) (verified 24 March 2010). Note: For this article, all information from the source that does not comply with organic certification regulations has been removed.

Vicia villosa

Type: winter annual or summer annual legume
Roles: N source, weed suppressor, topsoil conditioner, reduce erosion
Mix with: small grains, field peas, bell beans, crimson clover, buckwheat

Few legumes match hairy vetch for spring residue production or nitrogen contribution. Widely adapted and winter hardy through Hardiness Zone 4 and into Zone 3 (with snow cover), hairy vetch is a top N provider in temperate and subtropical regions. The cover grows slowly in fall, but root development continues over winter. Growth quickens in spring, when hairy vetch becomes a sprawling vine up to 12 feet long. Field height rarely exceeds 3 feet unless the vetch is supported by another crop. Its abundant, viney biomass can be a benefit and a challenge. The stand smothers spring weeds, however, and can help you replace all or most N fertilizer needs for late-planted crops.

Benefits

Nitrogen source

Hairy vetch delivers heavy contributions of mineralized N (readily available to the following cash crop). It can provide sufficient N for many vegetable crops, partially replace N fertilizer for corn or cotton, and increase cash crop N efficiency for higher yield.

In some parts of California and the East in Zone 6, hairy vetch provides its maximum N by safe corn planting dates. In Zone 7 areas of the Southeast, the fit is not quite as good, but substantial N from vetch is often available before corn planting.

Corn planting date comparison trials with cover crops in Maryland show that planting as late as May 15 (the very end of the month-long local planting period) optimizes corn yield and profit from the system. Spring soil moisture was higher under the vetch or a vetch-rye mixture than under cereal rye or no cover crop. Killed vetch left on the surface conserved summer moisture for improved corn production (A. J. Clark, personal communication, 2007; Clark et al., 1995, 1997b, 2007a; Hanson et al., 1993; Lichtenberg et al., 1994).

Even without crediting its soil-improving benefits, hairy vetch increases N response and produces enough N to pay its way in many systems. Hairy vetch without fertilizer was the preferred option for “risk-averse” no-till corn farmers in Georgia, according to calculations comparing costs, production, and markets during the study. The economic risk comparison included crimson clover, wheat and winter fallow. Profit was higher, but less predictable, if 50 pounds of N were added to the vetch system (Ott and Hargrove, 1989).

Hairy vetch ahead of no-till corn was also the preferred option for risk averse farmers in a three-year Maryland study that also included fallow and winter wheat ahead of the corn. The vetch-corn system maintained its economic advantage when the cost of vetch was projected at maximum historic levels, fertilizer N price was decreased, and the herbicide cost to control future volunteer vetch was factored in (Hanson et al., 1993). In a related study on the Maryland Coastal Plain, hairy vetch proved to be the most profitable fall-planted, spring-desiccated legume ahead of no-till corn, compared with Austrian winter peas and crimson clover (Lichtenberg et al., 1994).

In Wisconsin’s shorter growing season, hairy vetch planted after oat harvest provided a gross margin of $153/A in an oat/legume/corn rotation (1995 data). Profit was similar to using 160 lb. N/A in continuous corn, but with savings on fertilizer and corn rootworm insecticide (Stute and Posner, 1995).

Hairy vetch provides yield improvements beyond those attributable to N alone. These may be due to mulching effects, soil structure improvements leading to better moisture retention and crop root development, and soil biological activity and/or enhanced insect populations just below and just above the soil surface.

Soil conditioner

Hairy vetch can improve root zone water recharge over winter by reducing runoff and allowing more water to penetrate the soil profile through macropores created by the crop residue (Folorunso et al., 1992). Adding grasses that take up a lot of water can reduce the amount of infiltration and reduce the risk of leaching in soils with excess nutrients. Hairy vetch, especially an oats/hairy vetch mix, decreased surface ponding and soil crusting in loam and sandy loam soils. Researchers attribute this to dual cover crop benefits: their ability to enhance the stability of soil aggregates (particles), and to decrease the likelihood that the aggregates will disintegrate in water (Folorunso et al., 1992).

Hairy vetch improves topsoil tilth, creating a loose and friable soil structure. Vetch doesn’t build up long-term soil organic matter due to its tendency to break down completely. Vetch is a succulent crop, with a relatively low carbon to nitrogen ratio. Its C:N ratio ranges from 8:1 to 15:1, expressed as parts of C for each part of N. Rye C:N ratios range from 25:1 to 55:1, showing why it persists much longer under similar conditions than does vetch. Residue with a C:N ratio of 25:1 or more tends to immobilize N.

Early weed suppression

The vigorous spring growth of fall-seeded hairy vetch out-competes weeds, filling in where germination may be a bit spotty. Residue from killed hairy vetch has a weak allelopathic effect, but it smothers early weeds mostly by shading the soil. Its effectiveness wanes as it decomposes, falling off significantly after about three or four weeks. For optimal weed control with a hairy vetch mulch, select crops that form a quick canopy to compensate for the thinning mulch or use high-residue cultivators made to handle it. Mixing rye and crimson clover with hairy vetch (seeding rates of 30, 10, and 20 lb./A, respectively) extends weed control to five or six weeks, about the same as an all-rye mulch. Even better, the mix provides a legume N boost, protects soil in fall and winter better than legumes, yet avoids the potential crop-suppressing effect of a pure rye mulch on some vegetables.

A polyculture of crimson clover, cereal rye and hairy vetch used as a green manure cover crop for sweet corn.
Figure 1. A polyculture of crimson clover, cereal rye and hairy vetch used as a green manure cover crop for sweet corn. Planting polycultures increases plant and insect diversity, increases the number of ecosystem services, and decreases risk of crop failure. This photograph was taken in at the University of Florida's Plant Science Research and Education Unit in Citra, FL in early March, one week before termination. Photo credit: Danielle Treadwell, University of Florida.

Good with grains

For greater control of winter annual weeds and longer-lasting residue, mix hairy vetch with winter cereal grains such as rye, wheat or oats. Growing grain in a mixture with a legume not only lowers the overall C:N ratio of the combined residue compared with that of the grain, it may actually lower the C:N ratio of the small grain residue as well. This internal change causes the grain residue to break down faster, while accumulating the same levels of N as it did in a monoculture (Ranells and Wagger, 1997).

Moisture-thrifty

Hairy vetch is more drought tolerant than other vetches. It needs a bit of moisture to establish in fall and to resume vegetative growth in spring, but relatively little over winter when above-ground growth is minimal.

Phosphorus scavenger

Hairy vetch showed higher plant phosphorus (P) concentrations than crimson clover, red clover, or a crimson/ryegrass mixture in a Texas trial. Soil under hairy vetch also had the lowest level of P remaining after growers applied high amounts of poultry litter prior to vegetable crops (Earhart, 1996).

Fits many systems

Hairy vetch is ideal ahead of early-summer planted or transplanted crops, providing N and an organic mulch. Some Zone 5 Midwestern farmers with access to low-cost seed plant vetch after winter grain harvest in midsummer to produce whatever N it can until it winter-kills or survives to regrow in spring.

Widely adapted

Its high N production, vigorous growth, tolerance of diverse soil conditions, low fertility need, and winter hardiness make hairy vetch the most widely used of winter annual legumes.

Management

Establishment and Fieldwork

Hairy vetch can be no-tilled, drilled into a prepared seedbed, or broadcast. Dry conditions often reduce germination of hairy vetch. Drill seed at 15 to 20 lb./A, broadcast 25 to 30 lb./A. Select a higher rate if you are seeding in spring, late in the fall, or into a weedy or sloped field. Irrigation will help germination, particularly if broadcast seeded. Plant vetch 30 to 45 days before killing frost for winter annual management; in early spring for summer growth; or in July if you want to kill or incorporate it in fall or for a winter-killed mulch. Hairy vetch has a relatively high P and K requirement and, like all legumes, needs sufficient sulfur and prefers a pH between 6.0 and 7.0. However, it can survive through a broad pH range of 5.0 to 7.5 (Duke, 1981). In Minnesota, vetch can be interseeded into sunflower or corn at last cultivation. Sunflower should have at least four expanded leaves or yield will be reduced (Kandel et al., 1997, 2000). Farmers in the Northeast’s warmer areas plant vetch by mid-September to net 100 lb. available N/A by mid-May. Sown mid-August, an oats/hairy vetch mix can provide heavy residue (Harlow, 1994).

A mixture of rye (30%) and vetch (70%) was planted as a green manure for sweet corn. Cereal rye has a erect growing habit and serves as an excellent trellis for vining legumes like hairy vetch.
Figure 2. A mixture of rye (30%) and vetch (70%) was planted as a green manure for sweet corn. Cereal rye has a erect growing habit and serves as an excellent trellis for vining legumes like hairy vetch. Photo credit: Danielle Treadwell, University of Florida.

Rye/hairy vetch mixtures mingle and moderate the effects of each crop. The result is a “hybrid” cover crop that takes up and holds excess soil nitrate, fixes N, stops erosion, smothers weeds in spring and on into summer if not incorporated, contributes a moderate amount of N over a longer period than vetch alone, and offsets the N limiting effects of rye (Clark et al., 1994, 1997a, 1997b, 2007b; Sideman, 1991). Seed vetch/rye mixtures, at 15-25 lb. hairy vetch with 40-70 lb. rye/A (Clark et al., 1994; Sarrantonio, 1994). Overseeding (40 lb./A) at leaf-yellowing into soybeans can work if adequate rainfall and soil moisture are available prior to the onset of freezing weather. Overseeding into ripening corn (40 lb./A) or seeding at layby has not worked as consistently. Late overseeding into vegetables is possible, but remember that hairy vetch will not stand heavy traffic (Sarrantonio, 1994).

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. However, even in no-till systems, hairy vetch consistently provides very large N input (replacing up to 100 lb. N/A). 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. Mulch-retaining options include strip-tilling or mechanical killing (rotary mowing, flailing, cutting, sub-soil shearing with an undercutter, or chopping/flattening with a roller/crimper).

No-till corn into killed vetch

The best time for planting no-till corn 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 per year over 15 years for one researcher/farmer. He  killed 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. 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 (Townsend, 1994). 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 late-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 (Clark et al., 1995, 1997a, 1997b, 2007a). With hairy vetch and a vetch/rye mixture, summer soil water conservation by the cover crop residue had a greater impact on corn yield than spring moisture depletion by the growing cover crop (Clark et al., 1997b, 2007a).

Results in the other 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 (Clark et al., 2007a, 2007b). 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 (Hoffman et al., 1993), requiring calculation to determine if lower costs for tillage, weed control, and N outweigh the yield loss. Once vetch reaches about 50% bloom, it is easily killed by any mechanical treatment. 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 at 8 to 10 mph (Groff).

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.

University of Florida roller crimper. Roller crimpers terminate the crop by crimping the stems, thus interrupting the flow of nutrients and water through the plant. This system allows the plant residue to remain on the soil surface.
Figure 3. University of Florida roller crimper.

No-till, delayed kill

Farmers and researchers are increasingly using a roller/crimper to kill hairy vetch and other cover crops (ATTRA Question of the week). Jeff Moyer and others at the Rodale Institute in Kutztown, PA, roll hairy vetch and other cover crops in late May or early June (at about 50% flower). The modified roller is front-mounted, and corn is no-tilled on the same pass (The no-till + page). Also useful in killing hairy vetch on raised beds for vegetables and cotton is the improved prototype of an undercutter that leaves severed residue virtually undisturbed on the surface (Creamer et al., 1995). The undercutter tool includes a flat roller attachment, which, by itself, usually provides only partial suppression unless used after flowering.

Vetch incorporation

As a rule, to gauge the optimum hairy vetch kill date, credit vetch with adding 2 to 3 pounds of N per acre per sunny day after full spring growth begins. Usually, N contribution will be maximized by early bloom (10-25 percent) stage. 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 (UC SAREP Cover Crop Resource Page).

flail chop vetch and rye
Figure 4. Flail chopper terminating hairy vetch and rye. Photo credit: Danielle Treadwell, University of Florida.

Management Cautions

About 10 to 20 percent of vetch seed is “hard” seed that lays ungerminated in the soil for one or more seasons. This can cause a weed problem, especially in winter grains. In wheat, a variety of herbicides are available, depending on crop growth stage. After a corn crop that can utilize the vetch-produced N, you can establish a hay or pasture crop for several years. Don’t plant hairy vetch with a winter grain if you want to harvest grain for feed or sale. Production is difficult because vetch vines will pull down all but the strongest stalks. Grain contamination also is likely if the vetch goes to seed before grain harvest. Vetch seed is about the same size as wheat and barley kernels, making it hard and expensive to separate during seed cleaning (Sarrantonio, 1994). Grain price can be markedly reduced by only a few vetch seeds per bushel. A severe freeze with temperatures less than 5°F may kill hairy vetch if there is no snow cover, reducing or eliminating the stand and most of its N value. If winterkill is possible in your area, planting vetch with a hardy grain such as rye ensures spring soil protection.

Pest Management

In legume comparison trials, hairy vetch usually hosts numerous small insects and soil organisms (House and Alzugaray, 1989). Many are beneficial to crop production (see below), but others are pests. Soybean cyst nematode (Heterodera glycines) and root-knot nematode (Meliodogyne spp.) sometimes increase under hairy vetch. If you suspect that a field has nematodes, carefully sample the soil after hairy vetch. If the pests reach an economic threshold, plant nematode-resistant crops and consider using another cover crop. Other pests include cutworms (Sarrantonio, 1994) and southern corn rootworm (Buntin et al., 1994), which can be problems in no-till corn; tarnished plant bug, noted in coastal Massachusetts (Bugg et al., 1990), which readily disperses to other crops; and two-spotted spider mites in Oregon pear orchards (Flexner et al., 1991). Leaving unmowed remnant strips can lessen movement of disruptive pests while still allowing you to kill most of the cover crop (Bugg et al., 1990).

Larva of Multicolored Asian Lady Beetle, Harmonia axyridis  Steven Jacobs
Figure 5. Larva of Multicolored Asian Lady Beetle, Harmonia axyridis. Photo credit: Steven B. Jacobs, Pennsylvania State University.

Prominent among beneficial predators associated with hairy vetch are lady beetles, seven-spotted ladybeetles (Bugg et al., 1990), and bigeyed bugs (Geocaris spp.). Vetch harbors pea aphids (Acyrthosiphon pisum) and blue alfalfa aphids (Acyrthosiphon kondoi) that do not attack pecans but provide a food source for aphid-eating insects that can disperse into pecans (Bugg, 1991). Similarly, hairy vetch blossoms harbor flower thrips (Frankliniella spp.), which in turn attract important thrip predators such as insidious flower bugs (Orius insidiosus) and minute pirate bugs (Orius tristicolor). Two insects may reduce hairy vetch seed yield in heavy infestations: the vetch weevil or vetch bruchid. Rotate crops to alleviate buildup of these pests (Sarrantonio, 1994).

Crop Systems

In no-till systems, killed hairy vetch creates a short-term but effective spring/summer mulch, especially for transplants. The mulch retains moisture, allowing plants to use mineralized nutrients better than unmulched fields. The management challenge is that the mulch also lowers soil temperature, which may delay early season growth (Sarrantonio, 1994). One option is to capitalize on high quality, low-cost tomatoes that capture the late-season market premiums.

How you kill hairy vetch influences its ability to suppress weeds

Durability and effectiveness as a lightblocking mulch are greatest where the stalks are left whole. Hairy vetch severed at the roots or sickle-bar mowed lasts longer and blocks more light than flailed vetch, preventing more weed seeds from germinating (Creamer et al., 1995; Teasdale and Mohler, 1993). Southern farmers can use an overwintering hairy vetch crop in continuous no-till cotton. Vetch mixed with rye has provided similar or even increased yields compared with systems that include conventional tillage, winter fallow weed cover and up to 60 pounds of N fertilizer per acre. Typically, the cover crops are no-till drilled after shredding cotton stalks in late October. Covers are spray killed in mid-April ahead of cotton planting in May. With the relatively late fall planting, hairy vetch delivers only part of its potential N in this system. It adds cost, but supplies erosion control and long-term soil improvement (Bloodworth and Johnson, 1995). Cotton yields following incorporated hairy vetch were perennial winners for 35 years at a northwestern Louisiana USDA site. Soil organic matter improvement and erosion control were additional benefits (Millhollon, 1994).

Note: An unmowed rye/hairy vetch mix sustained a population of aphid-eating predators that was six times that of the unmowed volunteer weeds and 87 times that of mown grass and weeds (Bugg et al., 1991).

Other Options

Spring sowing is possible, but less desirable than fall establishment because it yields significantly less biomass than overwintering stands. Hot weather causes plants to languish. Hairy vetch makes only fair grazing material; livestock do not relish it.

Harvesting seed

Plant hairy vetch with grains if you intend to harvest the vetch for seed. Use a moderate seeding rate of 10 to 20 lb./A to keep the stand from getting too rank. Vetch seed pods will grow above the twining vetch vines and use the grain as a trellis, allowing you to run the cutter bar higher to reduce plugging the combine. Direct combine at mid-bloom to minimize shattering, or swath up to a week later. Seed is viable for at least five years if properly stored (Sarrantonio, 1994). If you want to save dollars by growing your own seed, be aware that the mature pods shatter easily, increasing the risk of volunteer weeds. To keep vetch with its nurse crop, harvest vetch with a winter cereal and keep seed co-mingled for planting. Check the mix carefully for weed seeds.

Comparative Notes

Hairy vetch is better adapted to sandy soils than crimson clover (Ranells and Wagger, 1997), but is less heat-tolerant than 'Lana' woollypod vetch.

Cultivars

'Madison', developed in Nebraska, tolerates cold better than other varieties. Hairy vetches produced in Oregon and California tend to be heat tolerant. This has resulted in two apparent types, both usually sold as “common” or “variety not stated” (VNS). One has noticeably hairy, bluish-green foliage with bluish flowers and is more cold-tolerant. The other type has smoother, deep-green foliage and pink to violet flowers. A closely related species, 'Lana' woollypod vetch (Vicia dasycarpa), was developed in Oregon and is less cold tolerant than Vicia villosa. Trials in southeastern Pennsylvania with many accessions of hairy vetch showed big flower vetch (Vicia grandiflora cv. Woodford) was the only vetch species hardier than hairy vetch. 'Early Cover' hairy vetch is about 10 days earlier than regular common seed. 'Purple Bounty', released in 2006, is a few days earlier and provides more biomass and better ground cover than 'Early Cover'.

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