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Introduction
A cover crop is any crop grown to provide living
ground cover. It can be planted with the main crop or
in rotation with it.
Growing cover crops is a best management practice to
help minimize soil erosion, prevent nutrient leaching,
provide nitrogen (N) for subsequent cash crops,
suppress weeds, sequester carbon, increase crop
diversity, and provide beneficial insect habitats. In
Idaho, cover crops can be planted in spring, summer, or
fall and rotated with a variety of crops, including
barley, alfalfa, potato, sugar beets, beans, and
vegetables.
By planting cover crops, Idaho producers benefit from
the following:
• Lower N fertilizer costs
• Higher soil organic matter contents
• Less wind erosion
• Scavenging and retention of soil nutrients
• Weed or insect control
• Production of a dual-purpose alternative forage
This guide features optimal cover crops for high-desert
farming systems in the intermountain West under
irrigated or low-moisture conditions. The specific
species and varieties listed in this publication were
tested under Idaho growing conditions through
numerous on-farm research trials. The species were
selected based on cold hardiness, biomass production,
N fixing and scavenging abilities, and forage potential.
For each species, information includes optimal planting
dates, N contribution, biomass production,
recommended cover crop mixtures, and estimated cost
for cover crop seed.
The cover crop species are divided into three groups:
(1) cereal and grass cover crops, (2) N-fixing cover
crops, and (3) brassica cover crops (includes radish,
turnip, mustard, and canola). Depending on your
cropping system, the species can be mixed to achieve
multiple management goals.
For additional general information on cover crop
seeding, refer to “Recommended Cover Crop Seeding
Methods and Tools,” which is listed in the references
section.
Nitrogen and Organic Matter
Cover crop selection should be based on the cropping
system’s needs, such as improving soil conditions or
managing weeds and pests. Planting a mixture of two
or more cover crops can help add N to the soil,
increase soil organic matter, scavenge nutrients, and
control weeds (figure 1).
Nitrogen-accumulating crops (legumes) and
N-scavenging cover crops (brassicas) can reduce the
need for N fertilizer. The availability of N from cover
crops is dependent on the N content in the cover crop
plant tissue, incorporation method, incorporation
timing, and amount of biomass. For example,
Cover Crops for High-Desert
Farming Systems in Idaho
Lauren Hunter, Christi Falen, and Amber Moore
BULLETIN 889
Figure 1. A cover crop mixture of canola, triticale, clover, and vetch
helps to scavenge nutrients, increase organic matter, fix N, and
control weeds. This multi-species cover crop was planted in
Lincoln County, Idaho, following grain harvest.
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incorporation of a thick stand of N-rich hairy vetch can
contribute a significant amount of N to the following
crop, while incorporation of N-poor triticale residues can
likely tie up N in the soil. Tools like the Idaho cover crop
calculator and publications like Estimating Plant-
Available Nitrogen Release from Cover Crops can help
growers estimate the N contribution from planted cover
crops (see references and further readings).
Legumes do not provide as much organic matter as
grasses or grains. A cover crop mixture that contains a
combination of legumes and small grains or grasses
contributes N and organic matter (figure 2). If growing
dual-purpose alternative forage is a goal, producers
should plant species with good forage potential that are
safe to graze at a higher seeding rate (figure 3). Dual-
purpose cover crops allow producers to gain an
economic advantage by grazing the crop before using
its residue for soil management.
Winter Hardiness, Tillage Practices,
and Irrigation
How producers plan to incorporate or manage residue
with their available equipment will determine which
species will work best. Some growers may prefer a
cover crop that dies in the winter, which makes residue
easier to manage in the spring before cash crop
planting. In contrast, species that survive the winter are
beneficial for producers looking to maximize yield,
resulting in higher contributions of N and organic
matter from additional spring growth. Dual-purpose
cover crop mixtures should include species that
produce both fall and spring forage. Cover crops that
winter-kill are advisable for producers who are new to
cover crops.
Common methods used to terminate cover crops in the
spring include tillage, herbicide, winter-kill, mowing, and
roller/crimper. Moldboard plows, rotary tillers, chisel or
disking plows, and spaders are examples of tillage tools.
Producers who do not want to incorporate cover crops
or employ minimum tillage can utilize no-till, strip-till,
or mulch-till equipment to plant succeeding crops into
existing residue. This practice is beneficial for
controlling weeds and minimizing disturbance to the
soil. However, under Idaho’s low-moisture
environment, not incorporating cover crop residue will
slow the release of N.
Producers can plant cover crops by broadcast seeding
with or without light incorporation of seed. Good seed-
to-soil contact and sufficient irrigation during
germination will ensure a good stand. Cereal producers
have the option to interseed cover crops into existing
cereal stubble in the fall or disk the field prior to
planting cover crops. Cover crops interseeded into
cereal stubble can be grazed in the fall for a dual-
purpose forage and cover crop mix.
Cereal and Grass Cover Crops
Cereal grains and grasses are successful cover crops
because they contribute organic matter to the soil,
reduce seed costs, are widely available, can be planted
with existing equipment, germinate quickly, require
minimal water, and increase residue yields when
planted with a legume. In Idaho, cereal and grass cover
crops are a good option to plant after a fall harvest and
leave for winter coverage. The large amount of residue
protects the soil surface from wind erosion, helps hold
soil nutrients, and conserves soil moisture.
Grains and grasses can be used as N catch crops,
scavenging residual N from fall-applied fertilizer or
manure/compost. This use of cereals and grasses will
help minimize N loss and conserve residual N for the
following growing season.
Figure 2. A cover crop mixture that contains legumes and a winter
cereal contributes both N and organic matter to the soil. At left is
a hairy vetch and triticale mix; at right is an Austrian winter pea
and triticale mix, Kimberly, Idaho.
Figure 3. A higher seeding rate of canola, triticale, clover, and
vetch makes this dual-purpose cover crop mix ideal for forage,
Minidoka County, Idaho.
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For forage use, cereal cover crops can be planted in
the spring, summer, or fall and used for fall and
spring grazing. A residual 3 to 4 inches should be left
for winter coverage and spring regrowth. The species
and varieties listed here are selected based on cold
hardiness, forage quality, yield potential, and
flexibility in a cover crop mix.
Even though rye grows well in Idaho, it is not
included in this publication due to producer concerns
with grain crop contamination. Following grain
harvest, volunteer grain stubble can be a part of your
planted cover crop mix.
Pearl Millet
Pearl millet, a warm-season annual grass, provides
beneficial ground cover and organic matter (figure 4).
It is most-widely grown in the southern U.S. as a high-
nutritive-value emergency forage. It is a tall, erect
grass that produces several stems from one plant. It
has an extensive root system, making it very drought
tolerant as well as a good nutrient scavenger. It does
not yield as much as sorghum Sudangrass but is safer
for grazing during the growing season because it
doesn’t have any prussic acid. Pearl millet is
considered a low-input crop; however, it does not
tolerate waterlogged soils.
Biomass production: Medium dry matter yields
Cold hardiness: Dies at the first frost. The best time to
grow pearl millet in Idaho is typically from June through
September or early October.
Planting dates: Summer, early fall
Mixtures: Grows well with peas and other legumes.
Seed cost: Medium
Sorghum Sudangrass
Sorghums and sorghum Sudangrasses are warm-
season annuals commonly grown for forage (figure
5). Special Effort, Enorma, HayKing, Forage King,
Cadan, and Nutri-Plus sorghum Sudangrasses have all
performed well under Idaho growing conditions.
Their fast growth and large biomass production are
beneficial for suppressing weeds and adding organic
matter to the soil.
Sudangrass can be grown on a variety of soil types,
survive in poorer soil, improve worn-out soils, and
penetrate compacted soil. It is drought resistant and
can scavenge nutrients due to its many secondary
roots. When grazing livestock on Sudangrass,
producers need to test plant tissue to avoid the risks
of high concentrations of nitrates and prussic acid.
After Sudangrass dies in the fall, the prussic acid
dissipates, but the nitrates do not.
Biomass production: High dry matter yields
Cold hardiness: Dies at the first frost. The best time to
grow Sudangrass in Idaho is typically from June
through September or early October.
Planting dates: Summer, early fall
Mixtures: Best planted alone in order to obtain
maximum amounts of organic matter for soil
incorporation and good weed control. It can be mixed
with other species at low seeding rates. Alternate-row
planting is an option to keep Sudangrass from
shading out other planted species.
Seed cost: Medium
Figure 4. A mid-June planting of pearl millet in August (left) and a
mid-August planting of pearl millet in October with some frost
kill, Kimberly, Idaho.
Figure 5. High-yielding, June-planted sorghum Sudangrass after
one month’s growth, Kimberly, Idaho.
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Triticale
Triticale is an annual cereal crop that produces a large
amount of biomass in a relatively short period of time.
Triticale works well on a variety of soil types and in a
variety of cropping systems. This crop can grow under
irrigated or limited-irrigation conditions and is
considered a low-input crop. Triticale is beneficial for
both animal forage and as a cover crop.
Biomass production: Medium to high dry matter yields
depending on the N available in the soil. High dry matter
yields when planted with a legume.
Cold hardiness: Winter varieties survive the winter;
spring varieties do not.
Planting dates: Spring, summer, fall
Mixtures: Plant with a legume, a brassica, or in a larger
mix of species.
Seed cost: Low
Winter Barley
Barley is a high-yielding annual cereal crop commonly
grown for forage and hay production. It matures early,
making it beneficial for early grazing with sufficient
time for regrowth as a cover crop.
Biomass production: Medium to high dry matter yields
depending on N available in the soil. High dry matter
yields when planted with a legume.
Cold hardiness: Winter varieties survive the winter;
spring varieties do not.
Planting dates: Spring, summer, fall
Mixtures: Plant with a legume, a brassica, or in a larger
mix of species.
Seed cost: Low
Winter Wheat
Winter wheat is an annual cereal forage that can grow
under irrigated or dryland conditions. Winter wheat
yields are usually lower than those of triticale but
higher than those of barley under irrigated conditions.
One tested cold-hardy winter wheat variety, Willow Creek,
is awnless, which makes it preferable for livestock forage.
It also stays in a vegetative stage longer than does triticale
or barley (figure 6). Crops that stay in the vegetative stage
longer release N later in the season than do early
maturing grasses. Other spring or winter wheat varieties
can be used, depending on local seed availability.
Biomass production: Medium to high dry matter yields
depending on the N available in the soil. Low to medium
yields under dryland conditions. High dry matter yields
when planted with a legume.
Cold hardiness: Survives the winter.
Planting dates: Fall
Mixtures: Plant with a legume, a brassica, or in a larger
mix of species.
Seed cost: Low
Nitrogen-Fixing Cover Crops
Peas, vetches, and other legumes are beneficial cover
crops because they contribute N to the soil. The symbiotic
rhizobia bacteria that live inside nodules on their roots fix
atmospheric N (figure 7). The N within the plant tissue is
in the form of proteins. A high protein content is what
also gives legumes a high nutrient value for animal forage.
Due to their higher seed cost, it is beneficial to plant
legumes in a mix with cereal crops, reducing the seeding
rate of legumes and supplementing with a less expensive
Figure 6. Winter barley (left) and Willow Creek winter wheat
(right) in June after a fall planting. Notice Willow Creek winter
wheat has not yet reached the reproductive stage. Crops that stay
in a vegetative stage longer release N later in the season than do
early maturing grasses.
Figure 7. Large root nodules on Austrian winter peas fix
atmospheric nitrogen, Shoshone, Idaho.
5
cereal seed. Cover crop research in Idaho revealed higher
yields when legumes were planted with a cereal crop
than in a 100% legume mix. The species and varieties
listed here were selected based on cold hardiness, forage
quality, and higher potential N contribution.
Arvika Forage Peas
Arvika forage pea—an annual pea with long vines—is
planted for its high yields and quality forage (figure 8).
In Idaho, Arvika forage peas have surpassed Austrian
winter peas for fall dry matter yields. This pea provides
weed control in the fall with its fast growth and in the
spring with its dense residue covering the soil surface.
Arvika forage pea is well suited for early spring N
release because the pea dies in the winter and the
residue starts to break down, releasing N in early
spring. Unlike Austrian winter peas and hairy vetch, it
does not require soil incorporation to release plant-
available N. Arvika forage peas die in the winter and
are recommended for organic systems.
Nitrogen contribution: Medium to high
Biomass production: Large dry matter yields when
planted alone or with cereal crops
Cold hardiness: Does not survive the winter, but
can survive repeated temperatures below freezing
for short periods in the fall.
Planting dates: Spring, summer, fall
Mixtures: Plant with a cereal cover crop,
brassica, or both.
Seed cost: Medium. Currently seed not widely available.
Austrian Winter Peas
Austrian winter peas (figure 9) are an excellent
cover crop due to their adequate yields, excellent N
contribution, and forage value. Irrigated Austrian
winter peas planted in Aberdeen, Idaho, produced
219 pounds of plant-available nitrogen per acre after
plowdown. Other trials in Idaho found Austrian
winter peas to survive and produce adequate
biomass under limited irrigation. Research in
Montana found that spring-planted malting barley
had a higher protein content after a fall planting and
spring plowdown of Austrian winter peas than when
grown after other legumes or a fallow system.
The purple flowers attract beneficial insects and
provide nectar for honeybees. Austrian winter peas
are easy to kill with disking or mowing after full
bloom stage. Plant peas for winter grazing early in
the fall; plants that have more growth left in the fall
are more susceptible to winter kill.
Nitrogen contribution: High
Biomass production: Medium dry matter yields
Cold hardiness: Cold hardy, with 50–75% surviving
the winter
Planting dates: Spring, summer, fall
Mixtures: Plant with a cereal or in a
multi-species mix.
Seed cost: Medium to high
Figure 8. Arvika forage peas (center) surrounded by sorghum
varieties on October 1, 2013. Crop planted August 14, 2013,
Kimberly, ID.
Figure 9. Higher-yielding Austrian winter pea growth in front of a
slower-growing chickling vetch, Shoshone, Idaho.
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Chickling Vetch
Chickling vetch is an annual viney pea (figure 10). In
Idaho under irrigated conditions it does not provide as
much N in the fall as hairy vetch, Austrian winter peas,
or Arvika forage peas. However, if it is planted in the
spring and allowed to grow the entire growing season,
it can produce more biomass and provide more N than
they do. Chickling vetch can perform well under
limited irrigation with a full season of growth. Unlike
hairy vetch, chickling vetch will die in the winter,
making it more suitable for organic systems.
Nitrogen contribution: Low to medium
Biomass production: Low to medium dry matter yields
Cold hardiness: Dies after a heavy frost.
Planting dates: Spring, summer
Mixtures: Plant alone or with a cereal crop.
Seed cost: Medium
Cicer Milkvetch
Cicer milkvetch is a perennial legume that spreads by
rhizomes (figure 11). This species is best suited as a
long-term cover crop or in a pasture mix. In Idaho,
cicer milkvetch has had lower yields compared to other
species. Due to its rhizomatous root system, cicer
milkvetch is good for erosion control and is considered
a good option for revegetating disturbed areas at higher
elevations. The showy flowers are good for home
garden use and for attracting beneficial insects. Cicer
milkvetch is not good for weed control because it
germinates and grows slowly.
Nitrogen contribution: Low N contribution due to low
production
Biomass production: Low dry matter yields
Cold hardiness: Cold hardy; survives the winter.
Planting dates: Early spring, summer
Mixtures: Plant cicer milkvetch with a cereal or grass.
Seed cost: Low to medium
Clovers
Clovers are commonly planted in a pasture forage mix
because they improve forage quality and contribute N
to the soil. Clovers are best suited for longer growing
periods because they are slow to establish and produce
less biomass compared to other legumes. As a result,
they are expensive cover crops if only planted for a
short period.
Hairy Vetch
Hairy vetch is a vine-like, vigorous annual cover crop
that behaves like a perennial (figure 12). It is widely
planted as a cover crop because it accumulates high
levels of N. Hairy vetch typically pays for itself with its
heavy N contribution in addition to its other soil-
improving benefits. Hairy vetch improves soil
structure, increases soil biological activity, and
promotes soil moisture retention. The vetch residue is
thought to create more stable soil aggregates
(particles), promoting better soil structure and
moisture retention.
In Idaho, a hairy vetch mix conserves more spring soil
moisture than a field planted in cereal rye or a field with
no cover crop. Hairy vetch planted at high seeding rates
can suppress weeds. Its fast spring growth helps to
outcompete weeds by shading the soil surface. Hairy
vetch also proves to be drought-tolerant and can survive
on a variety of soil types and under marginal field
Figure 10. Chickling vetch yields vary, but a full growing season
offers higher yields. Crop planted August 14, 2013, photographed
on October 10, 2013, Kimberly, ID.
Figure 11. Cicer milkvetch is a slow-growing species, more suitable
for a long-term planting than a short-season cover crop.
7
conditions. However, for organic systems hairy vetch
can become a weed problem; its persistent nature
makes it difficult to kill with tillage alone.
Nitrogen contribution: High
Biomass production: Medium dry matter yields
Cold hardiness: One of the more cold-hardy legume
cover crop species; it survives the winter.
Planting dates: Spring, summer, fall
Mixtures: Blending hairy vetch with a cereal or grass
allows the vetch to climb the cereal stems, optimizing
photosynthesis and helping to lift and detangle the
vetch vine for better mechanical control for residue
management.
Seed cost: One of the more expensive legumes
Brassica Cover Crops
Optimal brassica species for high-desert cropping
systems include canola or rapeseed, radish, mustards,
and turnips. The large taproot and/or horizontal roots
on these cover crops allow them to scavenge nutrients
deep in the soil profile. When planted in the fall, the
taproots help to capture residual soil nutrients such as
N and phosphorus. Rapid spring decomposition release
these nutrients back into the soil for the succeeding
crop.
The taproot also penetrates deep into the soil, helping
to mitigate subsoil compaction. Research in northern
Idaho shows that the taproots of canola, oriental
mustard, and yellow mustard improve soil structure
and water-holding capacity and reduce nitrate leaching.
Livestock favor brassicas as a forage crop, but
producers should be aware that their nutrient
scavenging abilities can contribute to nitrate
accumulation in plant tissue.
Brassicas grow rapidly in the fall and spring, providing
excellent soil coverage for weed control. In potato
systems, brassicas are used to manage pests. The cover
crops release chemical compounds that are toxic to
some soilborne pathogens and pests such as fungi,
nematodes, and some weeds. Mustards typically have a
higher concentration of these chemicals.
This publication includes only canola and daikon
radish, but other radishes, turnips, and mustards are
equally suitable and perform well under Idaho growing
conditions. Brassica cover crops work well planted
alone or in a cover crop mix.
Canola
Canola, an annual, is a trademarked cultivar of rapeseed
(figure 13). As a cover crop, canola is used for controlling
erosion, suppressing weeds, controlling soilborne pests,
alleviating soil compaction, and scavenging nutrients.
Canola needs adequate N in the soil at planting for good
survival and biomass production. A fall planting of canola
with a fall application of compost or manure will capture
excess N and phosphorus and release them the following
spring through decomposition.
Cold hardiness: Survives the winter if given sufficient
time in the fall for biomass production
Planting dates: Summer, fall
Mixtures: Plant alone, with a cereal or legume,
or in a larger mix of species.
Seed cost: Medium
Figure 13. A canola and triticale mix.Figure 12. A high-yielding hairy vetch crop contributes N and
organic matter and provides good weed control. May-planted crop
in August at a high-elevation farm, Picabo, Idaho.
Daikon Radish
Like other radish varieties, daikon radish is beneficial for
suppressing weeds, cycling nutrients, and reducing soil
compaction (figure 14). It has a large taproot that can
grow 2 to 3 inches in diameter and up to 1 foot or more in
length. The aboveground foliage grows quickly, providing
excellent weed control. A fall planting of daikon radish
with a fall application of compost or manure will capture
excess N and phosphorus and release them the following
spring through decomposition.
Cold hardiness: Daikon radish is a cool-season cover
crop but will not survive the winter.
Planting dates: Summer, fall
Mixtures: Plant alone, with a cereal or legume, or in a
larger mix of species.
Seed cost: Medium
Issued in furtherance of cooperative extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, in
cooperation with the U.S. Department of Agriculture, Charlotte V. Eberlein, Director of University of Idaho Extension, University of
Idaho, Moscow, Idaho 83844. The University of Idaho provides equal opportunity in education and employment on the basis of race,
color, national origin, religion, sex, sexual orientation, age, disability, or status as a disabled veteran or Vietnam-era veteran, as
required by state and federal laws.
Published April 2014 © 2014 by the University of Idaho
References and Further Readings
Alternative Field Crops Manual. Available from:
http://www.hort.purdue.edu/newcrop/afcm/
Clark, A. (ed.). 2007. Managing Cover Crops Profitably, 3rd
ed. Handbook Series Book 9. Sustainable Agriculture
Research and Education.
Hunter, L.A., and Falen, C.L. 2012. Green Manure for Soil
Nutrient Management in a High-Desert (3700-5100’
Elevation) Farming System. Proceedings of the Idaho
Nutrient Management Conference, 2012 March 6, Jerome,
Idaho.
Idaho Cover Crop Calculator. Available from:
http://www.extension.uidaho.edu/nutrient/
Natural Resources Conservation Service. 2012. Agronomy
Technical Notes: Recommended Cover Crop Seeding
Methods and Tools. USDA. Available from:
https://prod.nrcs.usda.gov/Internet/FSE_DOCUMENTS
/nrcs144p2_030755.pdf
Sullivan, D.M., and Andrews, N.D. 2012. Estimating Plant-
Available Nitrogen Release from Cover Crops. PNW 636.
Sullivan, P. 2003. Overview of Cover Crops and Green
Manures. Appropriate Technology Transfer for Rural
Areas. Available from
http://www.clemson.edu/sustainableag/IP024_covercrop.pdf
Winger, M., Ogle, D., St. John, L., and Stannard, M. 2012.
Cover Crops. USDA. Technical Note Agronomy No. 56.
Authors — Lauren Hunter, Extension Educator, University of
Idaho Extension, Blaine County; Christi Falen, former Extension
Educator, University of Idaho Extension; Amber Moore, Extension
Soil Specialist, University of Idaho Twin Falls Research and
Extension Center
Photos — By Lauren Hunter (figures 2 left, 4 right, 8, 12) and
Christi Falen (figures 1, 2 right, 3, 4 left, 5, 6, 7, 9, 10, 11, 13, 14)
Acknowledgment — This publication was funded by a grant
from the Western Sustainable Agriculture Research & Education
Program. Learn more about the program at http://westernsare.org
Figure 14. Large taproot on an oilseed (left) and daikon radish
(right) helps till the soil and reduce soil compaction; the secondary
roots on oilseed radish help to scavenge nutrients and water.
