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MEDICS
Medicago spp.
Also called: black medic, burr (or bur) medic, burclover
Type: Winter annual or summer annual legume
Roles: N source, soil quality builder, weed suppressor,
erosion fighter
Mix with: Other medics; clovers and grasses; small
grains
See charts, p. 66 to 72, for ranking and management summary.
Once established, few other legumes outperform medics in soil-saving,
soil-building and—in some systems—forage, when summer
rainfall is less than 15 inches. They serve well in seasonally dry
areas from mild California to the harsh Northern Plains. With more
rainfall, however, they can produce almost as much biomass and N as
clovers. Perennial medics are self-reseeding with abundant “hard
seed” that can take several years to germinate. This makes medics
ideal for long rotations of forages and cash crops in the Northern
Plains and in cover crop mixtures in the drier areas of California.
Annual medics include 35 known species that vary
widely in plant habit, maturity date and cold tolerance. Most upright
varieties resemble alfalfa in their seeding year with a single stalk
and short taproot. Medics can produce more than 100 lb. N/A in the
Midwest under favorable conditions, but have the potential for 200
lb. N/A where the plants grow over winter. They germinate and grow
quickly when soil moisture is adequate, forming a thick ground cover
that holds soil in place. The more prostrate species of annual medic
provide better ground cover.
Significant annual types include: burr medic (M.
polymorpha), which grows up to 14 inches tall, is semi-erect
or prostrate, hairless, and offers great seed production and N-fixing
ability; barrel medic (M. truncatula), about 16 inches
tall, with many mid-season cultivars; and snail medic (M. scutellata),
which is a good biomass and N producer.
Southern spotted burr medic is a native M. polymorpha
cultivar with more winterhardiness than most of the current burr
medics, which are imported from Australia. See Southern
Burr Medic Offers Reseeding Persistence. Naturalized burr medic
seed is traded locally in California.
Annual medics broadcast in spring over wheat stubble in Michigan
reduced weed number and growth of spring annual weeds prior to no-till
corn planting the following spring. Spring -planted annual medics
produced dry matter yields similar to or greater than alfalfa by
July (373, 376).
Black medic (M. lupulina) is usually
called a perennial. It can improve soil, reduce diseases, save moisture
and boost grain protein when grown in rotations with grains in the
Northern Plains. GEORGE is the most widely used cultivar in dryland
areas of the Northern Plains. Black medic produces abundant seed.
Up to 96 percent of it is hard seed, much of it so hard seeded that
it won’t germinate for two years. Second-year growth may be
modest, but coverage improves in years three and four after the
initial seeding if competition is not excessive (422)
and grazing management is timely.
Jess Counts on GEORGE for N
and Feed
STANFORD, Mon.—Jess Alger can count on
13 inches of rainfall or less on his central Montana farm,
occasional hail damage, too few solar units to raise safflower
or millet, some bone-chilling winters without snow cover—
and George. That’s GEORGE black medic.
On-farm tests showed he got 87 lb. N/A and 3
percent organic matter on his Judith clay loam soils. He initially
seeded the medic on 10- inch row spacings with barley at 10
lb./A, his standard rate and seeding method. He grazed the
medic early in the second year, and then let it go to seed.
In year 3, he sprayed it with glyphosate in order to establish
a sorghum sudangrass hybrid as emergency forage on May 15.
He had several inches of growth when frost hit about June
10 and killed the tender grass.
The medic came on strong. He let it mature to
its full 12 inches to harvest it for seed. “It was already
laying over, but the pickup guards on my combine helped to
gather in about half the seed.” The other half pumped
up the seed bank for years ahead.
He did a comparison with side-by-side fields
of spring wheat. One followed a spring wheat crop, the other
he planted into a six-year-old stand of GEORGE medic. The
medic/wheat interplant yielded 29 bushels per acre—six
bushels less than the other field. But the interplanted grain
tested at 15 percent protein, a full percentage point higher.
Those are high yields for Alger’s area, partly due to
timely summer rain. “The yield drop with medic was mostly
a weed problem with Persian darnel,” Alger explains,
“but I now have that mostly under control.”
Jess continues to fine-tune his system to maximize
income and weed management. He became certified organic in
1999. He maintains the medic seed bank with no-till plantings
of GEORGE with a nurse crop of Austrian winter peas. He is
experimenting successfully with rye instead of summer fallow.
If weed pressure is high, medic fields are grazed
closely to prevent weeds from going to seed, then plowed.
Otherwise, he no-tills winter wheat into standing medic so
he can leave most of the medic in place, bury less seed and
allow GEORGE to rest more securely in his field.
Updated in 2007 by Andy Clark |
BENEFITS
Good N on low moisture. In dryland areas, most
legumes offer a choice between N production and excessive water
use. Medics earn a place in dryland crop rotations because they
provide N while conserving moisture comparable to bare-ground fallow
(230, 380).
Fallow is the intentional resting of soil for a season so it will
build up moisture and gain fertility by biological breakdown of
organic matter. Black medic increased spring wheat yield by about
92 percent compared with spring wheat following fallow, and also
appreciably raised the grain protein level (379).
GEORGE grows in a prostrate to ascending fashion and overwinters
well with snow cover in the Northern Plains.
April soil N value after black medic in one Montana test was 117
lb./A, about 2.5 times the fallow N level and the best of six cultivars
tested, all of which used less water than the fallow treatment (378).
In North Dakota, however, unrestricted medic growth depressed yield
of a following wheat crop (73).
Great N from more water. Under normal dryland
conditions, medics usually produce about 1 T dry matter/A, depending
on available soil moisture and fertility. When moisture is abundant,
medics can reach their full potential of 3 T/A of 3.5 to 4 percent
plant-tissue nitrogen, contributing more than 200 lb. N/A (201,
422).
Fight weeds. Quick spring regrowth suppresses
early weeds. Fall weeds are controlled by medic regrowth after harvest,
whether the medic stand is overseeded or interplanted with the grain,
or the grain is seeded into an established medic stand. In California
orchards and vineyards where winters are rainy instead of frigid,
medics mixed with other grasses and legumes provide a continuous
cover that crowds out weeds. In those situations, medics help reduce
weed seed production for the long-term.
Boost organic matter. Good stands of medics in
well drained soil can contribute sufficient residue to build soil
organic matter levels. One Indiana test reported a yield of more
than 9,000 lb. dry matter/A from a springs own barrel medic (164).
Reduce soil erosion. Medics can survive in summer
drought-prone areas where few other cultivated forage legumes would,
thanks to their hard-seeded tendency and drought tolerance. Low,
dense vegetation breaks raindrop impact while roots may penetrate
5 feet deep to hold soil in place.
Tolerate regular mowing. Medics can be grazed
or mowed at intervals with no ill effects. They should be mowed
regularly to a height of 3 to 5 inches during the growing season
for best seed set and weed suppression. To increase the soil seed
bank, rest medic from blooming to seed maturation, then resume clipping
or grazing (285, 422,
435).
Provide good grazing. Green plants, dry plants
and burs of burr medic provide good forage, but solid stands can
cause bloat in cattle (422).
The burs are concentrated nutrition for winter forage, but lower
the value of fleece when they become embedded in wool. Annual medics
overseeded into row crops or vegetables can be grazed in fall after
cash crop harvest (376).
Reseeding. Black medic has a high percentage of
hard seed. Up to 90 percent has an outer shell that resists the
softening by water and soil chemicals that triggers germination
(286). Scarified seed will
achieve 95 percent germination, and 10-year old raw seed may still
be 50 percent viable (422).
Burr medic seed in the intact bur remains viable for a longer time
than hulled seed (120).
Their status as a resilient, reseeding forage makes medics the
basis for the “ley system” developed in dry areas of
Australia. Medics or subterranean clover pastured for several years
on Australian dry-lands help to store moisture and build up soil
productivity for a year of small grain production before being returned
to pasture. This use requires livestock for maximum economic benefit.
GEORGE black medic is prostrate, allowing other grasses and forbs
to become the overstory for grazing. It is well suited to cold winter
areas of Hardiness Zone 4, where it can stay green much of the winter
(6).
Quick starting. Black medic can germinate within
three days of planting (286).
About 45 days after mid-April planting in southern Illinois, two
annual medics were 20 inches tall and blooming. In the upper Midwest,
snail and burr medics achieve peak biomass about 60 days after planting.
An early August seeding of the annuals in southern Illinois germinated
well, stopped growing during a hot spell, then restarted. Growth
was similar to the spring-planted plots by September 29 when frost
hit. The plants stayed green until the temperature dipped to the
upper teens (201).
Widely acclimated. Species and cultivars vary
by up to seven weeks in their estimated length of time to flowering.
Be sure to select a species to fit your weather and crop rotation.
Southern Spotted Burr Medic
Offers Reseeding Persistence
While annual medics, in general, are hard seeded,
they usually cannot tolerate winters north of the Gulf South.
Southern spotted burr medic (Medicago arabica) shows
promise as a winter legume that can reseed for several years
from a single seed crop in Hardiness Zone 7 of the Southeast.
Once as widely grown as hairy vetch in the mid-South
region of the U.S., burr medic persists in non-cropland areas
because it is well adapted to the region (326,
327). A local accession
collected in northern Mississippi exhibits better cold hardiness
and insect resistance than commercially available (Australian)
annual medics.
In a replicated cold-hardiness trial spanning
several states, spotted burr medic flowered in mid-March,
about two weeks after SERENA, CIRCLE VALLEY or SANTIAGO burclover,
but two weeks before TIBBEE crimson clover. The burr medic
flowered over a longer period than crimson, matured seed slightly
sooner than TIBBEE but generally did not produce as much biomass.
The big advantage of spotted burr medic over
crimson clover was its ability to reseed for several years
from a single seed crop. In studies in several states, the
native medic successfully reseeded for at least two years
when growth was terminated two weeks after TIBBEE bloomed.
Only balansa clover (see Up
and Coming Cover Crops) reseeded as well as spotted burclover
(105). The burr medic
cultivar CIRCLE VALLEY successfully reseeded in a Louisiana
no-till cotton field for more than 10 years without special
management to maintain it (103).
Research in the Southeast showed that if Southern
spotted burr medic begins blooming March 23, it would form
viable seed by May 2, and reach maximum seed formation by
May 12. By allowing the cover crop to grow until 40 to 50
days after first bloom and managing the cropping system without
tillage that would bury burclover seeds too deeply, Southern
spotted burclover should successfully reseed for several years.
Native medic seed is being increased in cooperation
with the USDA -Natural Resources Conservation Service’s
Jamie Whitten Plant Materials Center, Coffeeville, Miss.,
for possible accelerated release to seed growers as a “source-identified”
cover crop.
Insect pests such as clover leaf weevil (Hypera
punctata Fabricius) and the alfalfa weevil (Hypera
postica Gyllenhal) preferentially attack medics over
other winter legume cover crops in the Southeast, and could
jeopardize seed production. These insects are easily controlled
with pyrethroid insecticides when weevils are in their second
instar growth stage. While not usually needed for single season
cover crop benefits, insecticides may be warranted in the
seeding year to ensure a reseeding crop for years to come. |
|
BLACK MEDIC
(Medicago lupulina) |
MANAGEMENT
Establishment
Annual medics offer great potential as a substitute for fallow in
dry northern regions of the U.S. with longer day length. Annual
medics need to fix as much N as winter peas or lentils and have
a competitive establishment cost per acre to be as valuable as these
better-known legume green manures (383).
Medics are widely adapted to soils that are reasonably fertile,
but not distinctly acid or alkaline. Excessive field moisture early
in the season can significantly reduce medic stands (373).
Acid-tolerant rhizobial strains may help some cool-season medics,
especially barrel medic, to grow on sites that otherwise would be
inhospitable (422).
To reduce economic risk in fields where you’ve never grown
medic, sow a mixture of medics with variable seed size and maturation
dates. In dry areas of California, medic monocultures are planted
at a rate of 2 to 6 lb./A, while the rate with grasses or clovers
is 6 to 12 lb./A (422).
Establishment options vary depending on climate and crop system:
 Early
spring—clear seed. Drill 1/4 to 1/2 inch deep (using
a double-disk or hoe-type drill) into a firm seed bed as you would
for alfalfa. Rolling is recommended before or after seeding to
improve seed-soil contact and moisture in the seed zone. Seeding
rate is 8 to 10 lb./A for black medic, 12 to 20 lb./A for larger-seeded
(snail, gamma and burr) annual medics. In the arid Northern Plains,
fall germination and winter survival are dependable, although
spring planting also has worked.
Spring
grain nurse crop. Barley, oats, spring wheat and flax
can serve as nurse crops for medic, greatly reducing weed pressure
in the seeding year. The drawback is that nurse crops will reduce
first-year seed production if you are trying to establish a black
medic seed bank. To increase the soil seed reserve for a long-term
black medic stand (germinating from hard seed), allow the medic
to blossom, mature and reseed during its second year.
Corn
overseed. SANTIAGO burr medic and SAVA snail medic were
successfully established in no-till corn three to six weeks after
corn planting during a two-year trial in Michigan. Corn yield
was reduced if medics were seeded up to 14 days after corn planting.
Waiting 28 days did not affect corn yield, but medic biomass production
was reduced by 50% (219).
Where medic and corn work together, such as California, maximize
medic survival during the corn canopy period by seeding early
(when corn is eight to 16 inches tall) and heavy (15 to 20 lb./A) to build up medic root reserves (47,
422).
After
wheat harvest. MOGUL barrel medic seeded after wheat
harvest produced 119 lb. N/A in southern Michigan, more than double
the N production of red clover seeded at the same time (373).
In Montana, mid-season establishment of snail medic after wheat
works only in years with adequate precipitation, when it smothers
weeds, builds up N, then winterkills for a soil-holding organic
mulch (72).
Autumn
seeding. Where winters are rainy in California, medics
are planted in October as winter annuals (436).
Plant about the same time as crimson clover in the Southeast,
Zones 7 and 8.
Killing
Medics are easy to control by light tillage or herbicides. They
reseed up to three times per summer, dying back naturally each time.
Medics in the vegetative stage do not tolerate field traffic.
Field Management
Black medic>small grain rotations developed in Montana
count on successful self-reseeding of medic stands for grazing by
sheep or cattle. A month of summer grazing improves the economics
of rotation by supplying forage for about one animal unit per acre.
In this system, established self-reseeding black medic plowed down
as green manure in alternate years improved spring wheat yield by
about 50 percent compared to fallow (380).
Black medic is a dual-use legume in this adapted “ley”
system. Livestock graze the legume in the "medic years”
when the cover crop accumulates biomass and contributes N to the
soil. Cash crops can be no-tilled into killed medic, or the legume
can be incorporated.
A well-established black medic stand can reduce costs compared
with annual crops by coming back for many years. However, without
the livestock grazing benefit to supply additional utilization,
water-efficient legumes such as lentils and Austrian winter peas
will probably be more effective N sources. Further, the long-lived
seed bank that black medic establishes may be undesirable for some
cash crop rotations (383).
Use of medics for grain production in the upper Midwest has given
inconsistent results. Berseem clover may be a better choice in many
situations. In a series of trials in Ohio, Michigan, Wisconsin and
Minnesota, medic sometimes reduced corn yield and did not provide
enough weed control or N to justify its use under current cash grain
prices, even when premiums for pesticide- free corn were evaluated
(141, 219,
373, 374,
376, 456,
457). One Michigan farmer’s
situation is fairly typical. He established annual medic at 10 lb./A
when his ridge-tilled corn was about knee high. The legume germinated,
but didn’t grow well or provide weed suppression until after
corn dry-down in mid-September. The medic put on about 10 inches
of growth before winterkilling, enough for effective winter erosion
protection (201).
Black medic and two annual medics produced 50 to 150 lb. N/A when
interplanted with standard and semi-dwarf barley in a Minnesota
trial. Annual MOGUL produced the most biomass by fall, but also
reduced barley yields. GEORGE was the least competitive and fixed
55 to 120 lb. N/A. The taller barley was more competitive, indicating
that taller small grain cultivars should be used to favor grain
production over medic stand development (289).
Midwestern farmers can overseed annual medic or a medic/grass mixture
into wheat in very early spring for excellent early summer grazing.
With timely moisture, you can get a hay cutting within nine to 10
weeks after germination, and some species will keep working to produce
a second cutting. Regrowth comes from lateral stems, so don’t
clip or graze lower than 4 or 5 inches if you want regrowth. To
avoid bloat, manage as you would alfalfa (201).
Annual medics can achieve their full potential when planted after
a short-season spring crop such as processing peas or lettuce. Wisconsin
tests at six locations showed medic produced an average of 2.2T/A
when sown in the late June or early July (399).
Early planting in this window with a late frost could give both
forage and N-bearing residue, protecting soil and adding spring
fertility. Take steps to reduce weed pressure in solid seedings,
especially in early July.
In another Michigan comparison, winter canola (Brassica napus)
yields were similar after a green manure comparison of two medics,
berseem clover and NITRO annual alfalfa. All the covers were clear
(sole-crop) seeded in early May after pre-plant incorporated herbicide
treatment, and were plowed down 90 days later. Harvesting the medics
at 60 days as forage did not significantly lessen their green manure
value (373).
In the mid-Atlantic at the USDA Beltsville, MD. site, medics have
been difficult to establish by over-seeding at vegetable planting
or at final cultivation of sweet corn.
Pest Management
Under water logged conditions for which they are ill-suited, annual
medics are susceptible to diseases like Rhizoctonia, Phytophthora
and Fusarium.
Burr medic harbors abundant lygus bugs in spring. It also appears
to be particularly prone to outbreaks of the two-spotted spider
mite, a pest found in many West Coast orchards (422).
Pods and viable seeds develop without pollinators because most
annual medics have no floral nectaries (120).
COMPARATIVE NOTES
Snail medic produced about the same biomass and
N as red clover when both legumes were spring sown with an oats
nurse crop into a disked seedbed in Wisconsin. Yields averaged over
one wet year and one dry year were about 1T dry matter and 60 lb.
N/A (141).
Medics can establish and survive better than subterranean clover
in times of low rainfall, and are more competitive with grasses.
A short period of moisture will allow medic to germinate and send
down its fast-growing taproot, while sub-clover needs more consistent
moisture for its shallower, slower growing roots (422).
Medics are more susceptible than subclover to seed production loss
from closely mowing densely planted erect stalks. Burr and barrel
medics are not as effective as subclover at absorbing phosphorus
(422).
Medics may survive where true clovers (Trifolium spp.)
fail due to droughty conditions (422)
if there is at least 12 in. of rain per year (292).
Medics grow well in mixtures with grasses and clovers, but don’t
perform well with red clover (422,
263). Once established, black
medic handles frost better than crimson or red clover.
GEORGE grows more slowly than yellow blossom sweetclover in spring
of the second year, but it starts flowering earlier. It uses less
water in the 2- to 4-foot depth than sweetclover, soybeans or hairy
vetch seeded at the same time.
Annual Medic Cultivars. Species and cultivars
of annual medic vary significantly in their drymatter production,
crude protein concentration and total N. Check with local or regional
forage specialists for cultivar recommendations
Burr medic (also called burclover) cultivars are
the best known of the annual medics. They branch profusely at the
base, and send out prostrate stems that grow more erect in dense
stands (422). They grow quickly
in response to fall California rains and fix from 55 to 90 lb. N/A,
nearly as much as true clovers (294,
422). Most stands are volunteer
and can be encouraged by proper grazing, cultivation or fertilization.
Selected cultivars include SERENA (an early bloomer), and CIRCLE
VALLEY, both of which have fair tolerance to Egyptian alfalfa weevil
(435). SANTIAGO blooms later
than SERENA. Early burr medics flower in about 62 days in California,
ranging up to 96 days for mid-season cultivars (422).
Naturalized and imported burr medic proved the best type of burclover
for self-reseeding cover crops in several years of trials run from
northern California into Mexico in the 1990s. While some of the
naturalized strains have been self-reseeding for 30 years in some
orchards, Extension specialists say the commercial cultivars may
be preferable because they are widely available and better documented.
Established burr medic tolerates shade as a common volunteer in
the understories of California walnut orchards, which are heavily
shaded from April through November. However, in Michigan trials
over several years, SANTIAGO (a burr medic with no spines on its
burs) failed to establish satisfactorily when it was overseeded
into corn and soybeans at layby. Researchers suspect the crop canopy
shaded the medic too soon after planting, and that earlier overseeding
may have allowed the medic to establish.
There are at least 10 cultivars of barrel medic.
Dates of first flowering for barrel medics range from 80 to 105
days after germination, and seed count per pound ranges from 110,000
for HANAFORD to 260,000 for SEPHI (422).
A leading new cultivar, SEPHI, flowers about a week earlier than
JEMALONG, commonly used in California (251,
422).SEPHI, a mid-season cultivar,
has a more erect habit for better winter production, is adapted
to high- and low-rainfall areas, yields more seed and biomass than
others, has good tolerance to Egyptian alfalfa weevil and high tolerance
to spotted alfalfa aphid and blue green aphid. It is susceptible
to pea aphid.
Snail medic (M. scutellata) is a prolific
seed producer. Quick germination and maturity can lead to three
crops (two reseedings) in a single season from a spring planting
in the Midwest (373). MOGUL
barrel medic grew the most biomass in a barley intercrop, compared
with SANTIAGO burr medic and GEORGE black medic in a four-site Minnesota
trial. It frequently reduced barley yields, particularly those of
a semi-dwarf barley variety, but increased weed suppression and
N and biomass production (289).
In a Michigan test of forage legumes for emergency forage use,
MOGUL barrel medic produced 1.5 T dry matter/A
compared to about 1 T/A for SAVA snail medic and SANTIAGO burr
medic (M. polymorpha). Nitrogen production was
66 lb./A for MOGUL, 46 for SAVA and 22 for SANTIAGO. The seeding
rate for SAVA medic is 29 lb./A, more than twice the 13 lb./A recommended
for clear seedings of MOGUL and SANTIAGO (373,
376).
In a California pasture comparison of three annual medics, JEMALONG
barrel had the highest level of seed reserves in
the soil after six years, but didn’t continue into the seventh
year after the initial seeding. GAMMA medic (M. rugosa)
had the highest first-year seed production but re-established poorly,
apparently due to a low hard seed content. All the medics re-established
better under permanent pasture than under any rotational system
involving tillage (94, 422).
Seed sources. See Seed
Suppliers.
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