This document provides an overview of how the NRCS Cover Crop (340) conservation practice can be implemented on organic operations. It discusses different purposes for the practice’s use, design considerations, and how installation might differ in organic systems. Specifically, it outlines techniques and specifications to help NRCS conservationists and partners meet the requirements of the NRCS Cover Crop (340) practice standard and comply with USDA National Organic Program regulations.
Cover Crop (340)
in Organic Systems
Oregon Implementation Guide
March 2014
National Center for
Appropriate Technology (NCAT)
www.ncat.org
Oregon Tilth
www.tilth.org
Xerces Society
www.xerces.org
1
Contents
Purpose ………………………………………………………3
Cover Crops in Organic Systems …………………….3
National Organic Program Regulations ……………4
Selecting a Cover Crop ………………………………….4
Table 1. Optimizing Cover Crop Objectives ……..6
Table 2. Examples of Cover Crops
for Organic Production ………………………………….7
Field Preparation ………………………………………….9
Planting …………………………………………………….10
Figure 2. Six-foot-tall fava bean cover crop, Fong Farms, Woodland,
California 2006.
Table 3. Cover Crop Planting Methods ………….12
Cover Crop Termination Options …………………13
Annual Cover Cropping in Perennial Systems ….16
Appendix A.
Table 4. Cover Crop Interseeding Systems ………17
Funded by a grant from
Western Sustainable
Agriculture Research
and Education (WSARE).
Appendix B.
References and Resources …………………………….18
Copyright © NCAT and Oregon Tilth 2013
www.attra.ncat.org www.tilth.org
ACKNOWLEDGMENTS
Authors Rex Dufour (National Center for Appropriate Technology); Sarah Brown, Ben Bowell and Carrie Sendak
(Oregon Tilth); Mace Vaughan and Eric Mader (Xerces Society)
Contributors and Reviewers Nick Andrews and Stephen Machado (Oregon State University); Eric Brennan (USDA
Agricultural Research Service); Doug Collins, Steve Fransen, and David Granatstein (Washington State University);
Christi Falen and Lauren Hunter (University of Idaho); Giulio Ferruzzi, Karen Lowell, Angie Quintana-Jones, Mary
Beth Smith, and Denise Troxell (Natural Resources Conservation Service); Jennifer Miller (Northwest Center for
Alternatives to Pesticides)
Design and layout Tim Kirkpatrick (Wonder Parade, LLC); Karen Van Epen (National Center for Appropriate
Technology)
Photos Rex Dufour (NCAT) unless otherwise noted
Figure 1. (on front cover) Crimson clover and phacelia cover crop between leeks, grown to provide beneficial insect
habitat, over-winter erosion control, weed suppressant and contributes to organic biomass in the soil. (Ben Bowell)
For more information or questions, contact Ben Bowell at Benjamin.Bowell@por.usda.gov or 503-580-4767
2
Purpose
This document provides an overview of how the NRCS Cover Crop (340) conservation practice can be
implemented on organic operations. It discusses different purposes for the practice’s use, design considerations,
and how installation might differ in organic systems. Specifically, it outlines techniques and specifications to help
NRCS conservationists and partners meet the requirements of the NRCS Cover Crop (340) practice standard
and comply with USDA National Organic Program regulations.
Cover Crops in Organic Systems
The purposes for cover cropping in organic systems do not differ from those in conventionally managed systems.
However, the role of cover crops to support soil function takes on greater importance in organic systems because
the use of synthetic chemical fertilizers and pesticides are generally not allowed. Cover crops are also essential on
organic operations to meet National Organic Program (NOP) requirements to minimize erosion; maintain or
improve soil organic matter and the biological condition of the soil; and manage crop nutrients and soil fertility
through cover crops and other techniques (see text box on next page).
Producers and planners may decide to implement cover crops to address a variety of purposes on a particular
operation. This purpose will impact design and implementation of the practice.
The following purposes are recognized by the NRCS Cover Crop (340) standard:
➣ Reduce erosion from wind and water;
➣ Increase soil organic matter content;
➣ Capture and recycle or redistribute nutrients in the soil profile;
➣ Promote biological nitrogen fixation and reduce energy use;
➣ Increase biodiversity;
➣ Suppress weeds and pests;
➣ Manage soil moisture;
➣ Minimize and reduce soil compaction; and
➣ Reduce particulate emissions into the atmosphere.
Depending on the purpose, cover crops can also be used to provide supplemental forage, but this use may be
restricted by NRCS cover crop guidelines.
3
Relevant National Organic Program (NOP) Regulations
The entire NOP regulautions, as well as lists of approved and prohibited materials and other
information can be found at the NOP website: www.ams.usda.gov/AMSv1.0/nop
Section 205.203 Soil Fertility and Crop Nutrient Management Practice Standard
(a) The producer must select and implement tillage and cultivation practices that maintain or improve
the physical, chemical, and biological condition of soil and minimize soil erosion.
(b) The producer must manage crop nutrients and soil fertility through rotations, cover crops, and the
application of plant and animal materials.
(c) The producer must manage plant and animal materials to maintain or improve soil organic matter
content in a manner that does not contribute to contamination of crops, soil, or water by plant
nutrients, pathogenic organisms, heavy metals, or residues of prohibited substances.
Section 205.204 Seeds and Planting Stock Practice Standard
(a) The producer must use organically grown seeds, annual seedlings, and planting stock: Except, That,
(1) Nonorganically produced, untreated seeds and planting stock may be used to produce an organic
crop when an equivalent organically produced variety is not commercially available:
Except, that, organically produced seed must be used for the production of edible sprouts;
(2) Nonorganically produced seeds and planting stock that have been treated with a substance
included on the National List of synthetic substances allowed for use in organic crop production may
be used to produce an organic crop when an equivalent organically produced or untreated variety is
not commercially available*;
(3) Seeds, annual seedlings, and planting stock treated with prohibited substances may be used to
produce an organic crop when the application of the materials is a requirement of Federal or State
phytosanitary regulations.
Section 205.205 Crop Rotation Practice Standard
The producer must implement a crop rotation including but not limited to sod, cover crops, green
manure crops, and catch crops that provide the following functions that are applicable to the operation:
(a) Maintain or improve soil organic matter content;
(b) Provide for pest management in annual and perennial crops;
(c) Manage deficient or excess plant nutrients; and
(d) Provide erosion control.
* Commercially Available: The ability to obtain a production input in an appropriate form, quality, or
quantity to fulfill an essential function in a system of organic production or handling, as determined by
the certifying agent in the course of reviewing the organic plan. (Sec. 205.2).
Selecting a Cover Crop
The main consideration when choosing a cover crop is to first identify the purpose and objectives for its use.
Subsequent factors to consider include seed availability, cost, crop rotation, and equipment for seeding and
incorporation. Table 1 on the following page identifies a selection of purposes for cover crop use and provides
related practices and techniques to help achieve those goals. Additionally, it includes recommendations for
appropriate cover crops to meet those goals.
4
Most cover crop stands are grasses, legumes or mixes of the two. Cover crop species can be grouped into six major
categories: cool season grasses; cool season legumes; cool season broadleaves; warm season grasses; warm season
legumes; and warm season broadleaves. Native annual forbes, legumes and brassicas are becoming more popular
for their support of pollinator and beneficial insect habitat.
Cover crop mixes, often referred to as cocktails, may be more expensive and could be more complicated to plant
than a single species cover crop; however, these cocktails can satisfy multiple purposes in one planting. They are
often more resilient, can provide a higher quality residue, and their carbon:nitrogen ratio can be targeted to satisfy
cover cropping objectives (see Treadwell et al., 2010). They may also provide better cover, weed suppression, and
biomass, especially during drought or other non-optimum conditions (Stika, 2013). A further advantage to
planting cover crop mixes, or rotating cover crops, may be to avoid buildup of plant pathogens or parasitic
nematode populations in the soil. It is more cost effective to limit mixtures to species that will reliably achieve
cover cropping objectives than to try too many species at once.
Some innovative examples and considerations for cover crop mixes include:
➣ Summer sown Sudan grass with crimson clover. The Sudan provides summer cover, weed suppression,
and organic matter; it is winter killed to provide mulch; and the crimson clover provides winter/spring
cover, nitrogen fixation, and habitat for beneficials.
➣ Late summer or fall sown phacelia and crimson clover. Phacelia is quick growing to provide cover and
habitat while the crimson establishes. The phacelia is winter killed and the crimson provides winter/spring
cover, nitrogen fixation, and habitat for beneficials.
➣ Cool season soil building mixes often include: rye or oats, winter peas, crimson clover, a vetch, and fava
beans. This mix can meet many purposes including: weed suppression, pollinator habitat, organic matter
building, and nitrogen fixation. (Figure 3)
➣ A cereal-legume mix provides more flexibility on the kill date for the cover crop plant available nitrogen
(PAN) provided by the cover crop. This is discussed in more detail in the Cover Crop Termination
Options section on page 13.
Figure 3. Fall seeded annual rye, vetch, winter peas, favas,
and crimson clover serve multiple purposes in
Western OR. (Sarah Brown)
Figure 4. A mixed bag of buckwheat and bell bean seed ready
for broadcasting. (Oregon Tilth)
The use of rhizobial seed inoculants for legumes is encouraged to ensure a robust nodulation of legume roots.
Make sure that the correct inoculant is used for each type of legume that is seeded. Inoculants may be required
by NRCS if the purpose of the cover crop is to provide biological nitrogen fixation. Producers should ensure
inoculants are not genetically modified and confirm with their certifier as needed before applying any new input
on their farm.
5
Table 1. Optimizing Cover Crop Objectives
Objective
Practice
Cover Crop Options
Weed
management
Increase legume seed rate by 100-200%, normal non-legume seeding
rates are adequate in most cases if the cover crop provides 100% ground
cover in approximately 30-40 days after planting. To ensure rapid cover
crop establishment: prepare fine seedbed, consider stale seedbed, ensure
good seed to soil contact, irrigate if needed. Planting with a drill with
close spacing between seed lines (i.e. 6-7”) is ideal to ensure an even
stand, however where broadcasting methods are used seeding rates
should be approximately 50% greater than for a drilled cover crop.
Maintain high percentage cereal or forb in cover crop mixtures
(i.e. 50-75% of solo stand).
Sudan grass*, buckwheat*, rye,
oats, and legume-grass mixes
Biological nitrogen
fixation
Use solo legume or mixed stands with high legume seeding rate (80-100%
of solo legume stand). Reduce cereal seeding rate (0-30% of solo cereal
stand); inoculate legumes unless same Rhizobia species is already well
established in soil. For maximum N release, terminate legumes at early
flowering. In stands with low percent legume, the risk of nitrogen
immobilization from mature cover crops is minimal when final cover crop
biomass contains at least 25% legume.
Vetch species, clovers, winter
peas, fava beans, cowpeas*,
and black medic*
Organic matter
contribution
Optimize cover crop biomass at termination; maintain high cereal or forb
seeding rate (50-75% of solo stand); terminate as late as possible without
delaying cash crop planting (i.e. late flowering); minimize tillage; rotate to
perennial cover crops when possible; consider high biomass cereals that
frost kill (i.e. Sudan grass, spring oats, etc.). Eliminate bare ground fallow.
Consider high biomass cereals
that frost kill (i.e. Sudan grass*,
spring oats*, etc.). Mixes work
well too: ryegrass, rye, lana
vetch, medic*, sweet clover, rye,
and barley
Enhance beneficial
insects
Use broadleaf species (legume or forb) that supply nectar, consider
beneficial insect blends; allow strips or whole fields to flower especially
when nectar and pollen sources are scarce (i.e. spring). Oregon-specific
plant lists, technical notes, and implementation guides be found at
Xerces’ Pollinator Conservation Resource Center.
Vetch species, red & crimson
clover, phacelia, and
buckwheat*
Reduced tillage
Minimize tillage during cover crop establishment and termination; relay
seed at establishment; at termination consider roller crimpers, flail
mowing, strip tillage and undercutting (under development in Pacific
Northwest rotations); terminate late in cover crop development but
before viable seed is formed (i.e. late anthesis or watery ripe for grains and
full bloom for vetches).
For relay seeded options see
Table 5. For more information
on no-till see ‘Organic No-Til
Farming’ listed in Resources,
Appendix B.
Plant pathogen
and nematode
management
Ensure that cover crops do not serve as alternative hosts to key soil-borne
pathogens in crop rotation. Some cover crops are known to reduce soilborne fungal and nematode pathogens in some rotations.
Radish, mustards, rye, sorghumsudan hybrid*, clover species,
and barley
Reduce
compaction
Select species with robust rooting ability to break up compaction and open Radish, sorghum- sudan
channels to support root growth of subsequent cash crops. Radishes that hybrid*, and sweet clover
are winter-killed often will leave open channels at the surface which
improves infiltration, surface drainage and soil warming.
* frost sensitive.
Please note these tips need to be adapted to fit in with various crop rotations and regional conditions.
This table is based on contributor’s professional experience and judgment in Oregon, Washington and
California. For more species specific information, visit eOrganic’s http://www.extension.org/pages/59454/cover-cropping-in-organic-farming-systems
Cover Cropping in Organic Systems.
Systems
6
Table 2. Examples of Cover Crops for Organic Production
Warm Season (spring sown)
Cover Crop
Seeding Rates
Advantages
Buckwheat
50 to 60 lbs/acre at 0.5
to 1.5 inches deep; 6 to 8
inch rows. For weed
suppression, use up to
96 lbs/ acre (2 bu./acre)
Fast-growing cover crop can be
incorporated 40 days after
planting and breaks down
quickly. Does well on poor soils.
Good alley crop for vineyards.
➣ Prefers lighter soil to heavy clays.
➣ Not frost or drought-tolerant.
➣ Avoid planting on high calcium soils.
Sorghum- Sudan
grass
Broadcast 40 to 50 lbs/
acre, or drill 35 to 40 lbs/
acre as deep as 2 inches
to reach moist soil.
Drought tolerant and wide pH
tolerance (5-9). Good crop for
rehabilitating poorly managed,
low-organic matter soils (high
biomass, good root structure,
weed and nematode
suppression.)
➣ Requires good soil fertility (70-100 lbs
40-50 lbs/acre minimum
rate for organic (75-100
lbs/acre for weed
suppression, or for 4-5
week cover crop)
Tolerates poor, sandy soils, but
needs good drainage. Can make
a green manure crop in 60 days.
Fast growing, good at
smothering weeds.
➣ Not winter hardy; a hard freeze will
Broadcast 70–120 lb
seed per acre, or drill
30–90 lb seed per acre.
Broadcast and cover,
or drill to a depth of 2
inches
Fast early growth effective to
smother weeds and cover
ground. In northern California,
a 75-day Lablab crop was
estimated to contribute 65–140
lb/acre of nitrogen. Very
palatable to livestock, and can
be mowed near to ground level
and regrow. Performs very well
with minimal irrigation.
➣ Requires well-drained soils.
Good N scavenger. Natural
fumigant potential against
bacteria, fungi, insects, and
weeds.
➣ Minimum soil temp. for planting is
Cold Season (fall sown)
Sunn Hemp
Crotalaria juncea
Hyacinth Bean
Lablab
purpureus
Brassicas
Canola: drill 5 to 10 lbs/
acre no deeper than ¾
in. or broadcast 8 to 14
lbs/acre.
Mustard: drill 5 to 12 lbs/
acre, ¼–¾ in. deep or
broadcast 10 to 15 lbs/
acre.
Radish: drill 8 to 12 lbs/
acre, ¼–½ in. deep, or
broadcast 12 to 20 lbs/
acre.
Turnip: drill 4 to 7 lbs/
acre about ½ in. deep or
broad- cast 10 to 12 lbs/
acre.
Considerations
N/acre) to produce medium biomass.
➣ Biomass can become woody, so
mowing midseason and fine
chopping of residue will aid
decomposition.
➣ Toxic compounds in the plant,
especially when young, can poison
animals; do not graze until the plant
is at least 18 inches tall.
kill it.
➣ Requires cowpea-type inoculant.
➣ Some species in Crotalaria genus
contain alkaloids poisonous to
livestock.
➣ Suppressive to root-knot nematode.
➣ Seed might be difficult to source.
➣ Inoculate with “cowpea-type”
rhizobia (Bradyrhizobium sp.)
➣ Does not easily nodulate with native
rhizobia.
➣ Susceptible to root-knot nematode,
bacterial wilt, and fusarium.
45°F; maximum is 85°F.
➣ Prefers pH range of 5.5 to 8.5.
➣ Avoid planting into fresh-killed
mustards as biotoxic compounds can
effect cash crop growth.
➣ Attractive to flea beetles and possible
alternate hosts of vegetable brassica
diseases such as clubroot
➣ Can become very weedy.
➣ Fall seeded mustards will generally
produce more biomass, a stronger
taproot, and require much less water.
7
Table 2. Examples of Cover Crops for Organic Production (continued)
Cover Crop
Advantages
Considerations
20:80 or 30:70
Fast growing with potential to
rye: vetch at 120 lbs/acre suppress weeds.
is standard, but for weed
suppression that rate
can be doubled or more.
➣ Depending on variety, about 20% of
15-20 lbs/acre drilled or
22-30 lbs/acre broadcast.
This can be increased for
more effective weed
suppression. Plant at
.25-.5 inch depth.
Grows well in mixes of small
grains, grasses and other
clovers. Flowers support bees
and minute pirate bugs (a mite
& thrip predator). Excellent for
grazing and haying.
➣ Wait 2-3 weeks after incorporation of
Phacelia
Phacelia z
7-12 lbs/acre drilled, 1118 lbs/acre broadcast
(use cultipacker or rake).
This can be increased for
more effective weed
suppression. Plant at .25
inch depth.
Attractive to flower flies (Syrphid
larvae eat aphids), bumble bees
and honey bees. Grows well in
dry soil and can limit nitrate
leaching if planted in early fall.
➣ Phacelia can host verticillium; flower
Fava beans
Vicia faba (bell
bean is a smallseeded selection
of fava bean)
(See Figure 2.)
80-200 lbs/acre (more
for weed suppression),
plant 1-4” (deeper range
for large-seeded
cultivars, shallow range
for smaller seeded
cultivars).
Fava beans do well in wide
range of soils, including heavy
clays. Fava bean residue persists
longer than that of other
leguminous cover crops, which
can help improve heavy soils.
➣ Technically a vetch, but is more
Rye and Vetch
Cold Season (fall sown)
Seeding Rates
Crimson Clover
vetch seed will not germinate in the
first season and can become a weed
in subsequent crops. For better weed
suppression, use higher seeding rates.
Check with local extension to
determine the appropriate variety as
many are available.
crimson to plant seeds or transplants
to allow decomposition.
➣ Secondary host for corn earworm
(also known as the tomato fruit worm
and cotton bollworm).
attractive to lygus (especially avoid
planting near strawberries).
➣ Will winterkill if temperatures fall to
mid-teens.
susceptible to frost damage, and fixes
a bit less N than most vetches (100150 lbs N/acre).
➣ Has extra-floral nectaries which
attract beneficials.
➣ Host to root-knot nematode.
Adapted from Clark (ed.) 2007 with input from reviewer’s professional experience and judgment in
Oregon, Washington, Idaho, and California.
Organic Seeding Rates: Higher seeding rates than are typically used on conventional farms
are important in organic systems to ensure that the cover crop produces a dense canopy and is
therefore able to suppress weeds. It may be worthwhile to increase the seeding rates by 1.5 to
3 times when there is heavy weed pressure or less than optimum fertility, seedbed prep, or
planting dates used (Brennan, et al, 2011, Schonbeck, 2011).
8
Field Preparation
To establish a cover crop successfully, field
preparation is the first critical component to
address. Two of the primary issues to consider
are weed management and the development
of a smooth seed bed for good seed-to-soil
contact. Ideally field preparation will mirror
that for annual cash crops, but can be less
intensive. Soil should be worked at an
appropriate moisture level to be free of clods
and ensure good seed-to-soil contact. In order
to gain the maximum benefit from the cover
crop, producers should provide appropriate
moisture. In some cases producers can relay
seed into young vegetable plantings at the
end of the weed management period and
establish cover crops with no seedbed
preparation or seed incorporation. If cash
crops are harvested very late, consider relay
seeding options, or broadcast annual ryegrass
and common vetch after harvest.
Figure 5. Stand of a vetch and oats, unbedded.
Annual vegetable operations may have fields with compaction or a plowpan layer where heavy equipment has
been run frequently. Clay soils with low organic matter, or those with heavy traffic and grazing, are especially
vulnerable to compaction. Compacted soils may not allow rainfall or irrigation water to infiltrate the lower soil
horizons, so some deep ripping may be required. While this is more of an issue for cash crops, it could impact the
establishment of a non-irrigated cover crop. Subsoiling should be done when soil is dry, often before seeding a fall
cover crop. Cover crops such as tillage radish can also be used specifically for the purpose of breaking up
compacted soils.
Once the field is sufficiently worked, it is critical to
plant as soon as possible. Even the slightest delay will
give germinating weed seeds a head start and a weed
infested cover crop can cause more problems than it
is worth. Competition from weeds can out-compete
cover crop growth requiring the producer to
prematurely incorporate the cover crop. Investing
some time and effort in creating a weed-free site
through methods such as solarization, stale seedbed,
or planting timing will pay off in better growth,
establishment, and biomass of the cover crop. These
methods are discussed in more detail in
‘Conservation Buffers in Organic Systems’.
Figure 6. Vetch and rye cover crop on beds.
9
Planting
Correct seeding depth helps improve stand establishment. Planting methods will vary depending on the purpose
for implementing cover crops. Seed or grain drills are the most common way to plant cover crops. No-till
planting into the previous crops’ residue is an option to reduce soil disturbance, but it may require specialized
equipment to handle heavy residues. Some seed suppliers and
Conservation Districts have no-till drills to rent. Seeding
options, arranged from those appropriate for small to large
acreages include: 1) broadcast by hand, 2) broadcast using a
“belly grinder” hand spin spreader or spread via a wheeled
walk-behind broadcast spreader or drop spreader, 3) tractor
driven spin spreaders or seed drills, 4) aerial broadcasting.
See Table 3 for more details about planting equipment and
methods. Options for working in the broadcasted seed include
irrigation or rainfall only, ring roller, spring-tooth harrow,
Figure 7: This Lilliston cultivator can be used for light
Lilliston cultivator (for larger seeds), or cultipacker to lightly
tillage for weed control in the top few inches of soil
work the top layer and provide good soil- to-seed contact. For
as well as for incorporation of cover crop residues.
small seeds, incorporate with rain or irrigation; if seedbed is crusted
(i.e. after cabbage on a silty soil) use a cultipacker. Larger seeds should
be covered by lightly scratching them into the soil surface.
One major problem with many methods of incorporating broadcast
seed is that often they place the seed too deep, requiring seeding rates
1.5 to 2 times higher than drilling. However, if not set properly, seed
drills can easily place seeds too deep as well. Conversely, it is equally
important not to place seeds too shallow and avoid them being eaten
by birds or drying out after germination and before establishment.
Use the recommended seed depth for each cover crop species and be
especially careful when seeding mixes. Some drills have an additional
hopper where smaller seeds like clover can be placed so that they are
broadcasted over a drilled grass seed. In
warm, dry conditions, plant a little
deeper (up to 50% deeper); in cool wet
conditions plant a little shallower
(Schonbeck, 2011).
Figure 8: A cultipacker, or ring-roller, is used
to firm the soil surface which helps seed-tosoil contact and breaks clods of soil. They
can be used successfully to lightly
incorporate cover crop seed.
Cover crops can be planted in the fall, spring, or even the summer. The timing
depends on the purpose for implementing the practice as well as equipment and the
cover crop species chosen. In the maritime Pacific Northwest, during most years a
cover crop planted in the fall can germinate and grow simply on rainfall. However,
it may require sprinkler irrigation in order to bring up a fall-planted cover crop if
the rains are late or it is a dry year. A summer cover crop will be more expensive
Figure 9: A broadcast seeder, or
because in most locations it will require irrigation and involves a higher opportunity
‘belly grinder’, appropriate for
small acreage seeding. (Earthway). cost as a cash crop is foregone during the main growing season. Drought tolerant
summer cover crops like Sudan x Sorghum hybrids can grow well with little to no
irrigation. Fall covers are generally used to “fix” low-cost N, scavenge residual nitrogen, compete with weeds and
protect the soil from erosion. Summer covers may be used for pest management, to smother warm season annual
weeds, or as a food source for beneficial insects.
10
Relay Seeding
Relay seeding, also known as over-seeding, under-seeding, or inter-seeding is the planting of a cover crop into a
growing cash crop. It can be done by air, broadcast or drill during a mid- or late-season cultivation of the cash
crop. The practice is more common in Midwest field crops, but can be another tool for western organic growers
and can be adapted to vegetables in the Northwest. This strategy promises to help annual cash crop growers
incorporate cover crops into their crop rotations with
late harvested cash crops. By not waiting for the cash
crop to be removed, earlier seeding provides quicker
canopy cover, reducing weed pressure and providing
over-winter erosion control.
In a western context, establishment of a relay-seeded
cover crop will depend on the type of irrigation used.
Sprinkler or furrow irrigation will support this
approach, but over-seeding into a field using buried
drip will likely not be successful. Ideally, overseeding should occur just prior to a rain event or
Figure 10. Eggplant oversewn with oats in Western Oregon.
scheduled irrigation. Over-seeding will likely require
(Nick Andrews)
higher seeding rates to overcome light, moisture, and
nutrient competition. Producers may consider using a more shade tolerant variety based upon the crop they are
seeding. White clover, annual ryegrass, rye, hairy vetch, crimson clover, red clover and sweet clover tolerate some
shading (Clark, 2007). Broadcasted seed should be heavy enough to fall through the crop canopy. More
information about relay-seeded cover crop opportunities and rotations can be found in Table 4, Appendix A.
Figure 11. Butternut squash oversewn with red clover in late June/early July just before last cultivation and
canopy closure. (Nick Andrews)
11
Table 3. Cover Crop Planting Methods
METHOD: Broadcast Seeders
Pros
Cons
➣
➣
➣
➣
➣
Inexpensive (many “belly grinders” are less than $100). See Figure 9 above.
➣ Easy to use.
➣ Drop seeders can accommodate both large and small seed.
➣ Can often accommodate poorly cleaned seed.
➣ Many models and sizes are commonly available, including hand-held
crank, wheeled walk-behind, and larger tractor or ATV-mounted
broadcasters; hand-powered turf grass seeders and larger tractor-drawn
“pasture- seeder” models.
Requires a smooth seed bed.
Seed should be pressed into the soil after planting.
Can be difficult to calibrate.
Some models of seeders cannot accommodate
large seed.
➣ Hand-powered models are time consuming for
large areas (over half an acre).
➣ Seeding rates need to be higher due to variable
seed depth and other factors.
Basic Instructions for Broadcasters and Drop Seeders:
Remove as much stubble as possible prior to seeding, creating a smooth, lightly-packed seedbed. The soil
surface can be lightly hand-raked or harrowed to break-up crusted surfaces, but do not cultivate the site
as this will bring up additional weed seed.
Seed of similar sizes can be mixed together and bulked up with an inert carrier ingredient such as sand,
fine-grained vermiculite, clay-based kitty litter, gypsum, or polenta (fine cornmeal). Use at least two to
three parts bulking agent for each part seed by volume. These inert carriers ensure even seed distribution
in the mix, visual feedback on where seed has been thrown, and make calibration easier.
The broadcast seeding equipment can be hand operated or tractor mounted (spin spreaders). They
should have a flow gate that closes down small enough to provide a slow, steady flow of the smallest
seed. Models with an internal agitator are preferred. Planting should begin with the flow gate set to the
narrowest opening to allow at least two perpendicular passes over the seed bed for even distribution.
Very large seed can be planted separately with the flow gate set to a wider opening.
For small sites (e.g., less than one to two acres), seed can also be hand broadcast (similar to scattering
poultry feed). When hand broadcasting, divide the seed into at least two batches, bulk the seed mix with
an inert carrier, using at least two to three parts bulking agent for each part seed by volume and sow each
batch separately. To ensure that seed is evenly distributed, scatter the first batch over the site while
walking in parallel passes across the site and then walk in passes perpendicular to the previous passes to
scatter the second batch.
Smaller seeds may not need to be covered with soil after planting; a water-filled turf grass roller (available
for rent at most hardware stores) or a cultipacker should be used to press the seed into the soil surface.
Larger seeds, including grains and legumes, should be covered by lightly scratching them into the soil
surface (but should not be cultipacked). Natural precipitation or light overhead irrigation can also help
ensure good seed-soil contact. A floating row-cover can be used if necessary to protect seeds and small
seedlings against predation.
METHOD: Drill
Pros
Cons
➣
➣
➣
➣
➣
No-till drills allow for planting of crop immediately after harvest of
previous crop.
➣ Potential for fewer disturbances of soil microorganisms and increased
carbon sequestration.
➣ Generally reduces fuel use on-farm due to decrease in working the soil.
➣ More even cover crop establishment.
➣ No need for separate operation to incorporate cover crop seed.
➣ Lower seed rates and seed cost.
➣ Local seed dealers or conservation districts may have drills for rent, saving
producers from having to buy new equipment.
12
Soils with high clay content must be “workable”.
No-till drills will not work well on hard clay ground.
No-till drills may require a larger tractor to use
due to extra weight and extra pressure on the
coulters to cut through plant residue.
Table 3. Cover Crop Planting Methods (continued)
Basic Instructions:
1. Do not till ground or incorporate plant residue prior to planting as this will bring up weed seeds into
the germination zone and destroy the weed-suppressive layer of crop residue. The purpose of no-till is to
plant the cover crop seed into an undisturbed bed.
2. Before drilling seeds, consider coulter positioning, planting depth, and type and size of plant residue.
3. If planting seed rows close together (closer than 6 to 8 inches), for faster canopy development the
openers usually must be staggered by mounting on two or more parallel bars (Pfost, 1993).
Cover Crop Termination Options
The method of cover crop termination is also related to the purpose for implementing cover crops and the
equipment available. In organic systems, cover crops can be terminated by frost, mowing, tillage/disking, rollercrimping, or some combination of mowing and tillage. The cover crop may not be burned. If cost-share assistance
is provided, termination by harvest or grazing may be restricted by NRCS (check with the Oregon state office).
Leaving the cover crop residue on the surface will protect the soil from wind and rain erosion and provide habitat
for spiders and ground beetles. However, it keeps the soil cooler, more moist, and can support higher populations
of slugs and snails. Planting or transplanting through the residue can be a problem unless the grower has access to
a no-till drill or no-till transplanter. There must be sufficient time between incorporation of the cover crop and
planting of the cash crop so that the cover crop residue has decomposed. Too much residue in the soil may attract
seed maggots and reduce germination of the cash crop. There are many variables that impact organic matter
decomposition but in general, producers will have to wait a four to five weeks before planting the subsequent crop.
Where early cash crops are planned, some growers are able to bury cover crops with a moldboard plow or remove
cover crop foliage with a silage chopper and disc under the stubble. It is sometimes possible to plant cash crops
immediately using both techniques.
The timing of termination will vary based on the crop and purpose.
➣ If planting only a legume, the best time to kill the crop for maximum PAN (Plant Available Nitrogen) is
at the budding growth stage.
➣ PAN from cereal cover crops is low to negative. At tillering (i.e. March) PAN can be zero to slightly
positive.
➣ For mixes with lower percentages of legumes, the crop should be killed earlier (i.e. before cereals reach
boot stage) so that the PAN is not tied up in the cereal’s carbon. If a cover crop is 75% legume, it will
behave essentially like a pure legume stand. However, if the legume is less than 25% of the cover crop
biomass, the cover should be terminated before cereals reach boot stage to avoid N immobilization
(Sullivan & Andrews, 2012).
➣ Cover crops grown to provide beneficial insect habitat should be allowed to reach maximum flowering but
be terminated before viable seed is set. Buckwheat, for example, is usually mowed 10 days after flowering
begins.
➣ Additional recommendations for termination considerations and timing are included in Table 1.
13
Figure 12: Vetch cover crop being flail mowed close to
the bed surface.
Mowing: Mowing is often used to terminate a flowering cover
crop before incorporation with a disc. It is a quick method to
ensure that cover crops do not go to seed. There are three basic
types of mowing machines: sickle bar, rotary and flail. Sickle
bars are fast and leave large pieces of stalks on the surface of the
ground. They are optimal for a slow decomposing mulch to
cover the soil. Rotary mowers (like those commonly used for
lawns) are useful in orchard settings to cut groundcover close to
trees, but they do not chop residue, leaf litter and prunings as
finely as flail mowers. Flail mowers generally require more
horsepower than rotary mowers and provide a finer chop may
allow for slightly quicker decomposition of the residue. Some
producers might opt to transplant directly into a mowed cover
crop, a minimum-till option that is usually easier to adopt than
roller crimpers. Be aware of challenges inherent with this
approach such as cooler, wetter soils and potential pest problems
(i.e rodents or slugs).
Figure 13: Flail-mowed vetch beds.
Tillage or Disking: Tillage or disking is generally used to
incorporate crop residue into the soil. If the amount of
residue is small, it might be left on the surface. Lilliston
cultivators can be used for light amounts of residue, but
for higher biomass covers, or for crops with dense root
masses, such as sorghum-sudan, disking or spading the
residue into the soil is needed before the next crop is
planted. If cover crop residues can be left on the surface,
the risk of erosion can be reduced.
14
Figure 14: Residue of vetch cover crop is about 3-4” thick. In this
situation the residue was be allowed to dry down, and then lightly
incorporated with a Lilliston cultivator.
Figure 15. A field one week after disking down a robust
legume cover crop and vetch. After the residue
decomposes further, the producer will disk one more
time prior to forming the planting beds.
Roller-crimping: Roller crimping is an appropriate option
if the purpose is to address soil quality as this method leaves
mulch on the soil surface which protects against erosion and
rain impacts. Additionally, this approach provides habitat for
spiders and ground beetles. Roller Crimping has been done
successfully in the Midwest, East and South, in combination
with no-till planters, but does not fit easily into raised bed
systems of the irrigated West. Research on roller crimpers in
organic systems in Salinas, California showed that raised beds
made it difficult to effectively roller crimp-kill the cover crop
as some of the cover crop fell into the furrows between beds.
Figure 16: This Salinas, California cover crop was a mix of rye
Regrowth of the cover crop and weed growth through the
on top of the beds and mustard in the furrows. (Eric Brennan)
rolled mulch are common problems in organic systems.
Cover crop varieties and timing of termination are crucial components to ensure success in an organic system.
Cover crops must reach early flowering to be effectively terminated with roller crimpers. For more information see
‘Organic No-Till Farming’ listed in resources, Appendix B.
Roller Crimper
Figure 17: This rye cover crop was terminated using a roller crimper.
(Eric Brennan)
Figure 18: Terminating cover crops on beds using a roller crimper.
(Eric Brennan)
Grazing: Depending on the cover crop’s purpose, grazing can be an effective method for cover crop management.
Grazing removes a substantial portion of the vegetation and may interfere with the goal of enhancing soil organic matter.
Grazing animals deposit manure and urine on the soil which has nutrient management as well as potential food safety
implications. Producers should consult with their organic certifier as well as NRCS prior to grazing any cover crops.
Figure 19: Walnut orchard floor prior to grazing.
Note the tall grasses and mix of cover crop species
compared to the grazed orchard floor on the right.
Figure 20: This organic walnut orchard has been grazed
by sheep which left the bell beans standing, but
devoured the Austrian peas, vetch, and in-row grasses.
15
Annual Cover Cropping in Perennial Systems
Most perennial producers will opt to incorporate perennial covers,
or Conservation Cover (327), rather than annual cover crops into
their systems. However, annual cover crops can provide many of
the same benefits to perennial systems.
Cover crops are an important component of organic orchard floor
management. They may be planted in the grass alley, legumes
planted for nitrogen, or flowering species planted for beneficial
insects. While living mulches in the tree row are often used, cover
crops can also be grown in the alley and used on the tree row.
Figure 21. Disking cover crops in every other alley in a
Often called “mow and blow,” this system blows clippings from
vineyard allows the grower access to all vines when the
mowing the alley on to the tree row with side discharge mowers.
rainy season arrives and keeps down dust.
The alley planting can be grass that produces biomass for mulch,
a legume to generate nitrogen, insectary plants, or any combination. This method can reduce irrigation, weed
control, and cost. Vineyards often use cover crops in alternate rows (see picture below) which are alternated the
following season. The cover crop planted rows allow the grower to use machinery in the alley more readily during
the wet season.
Considerations when choosing orchard or vineyard cover crop (Barney, 2012):
➣ Competition for moisture and nutrients;
➣ Habitat for rodents and rabbits, gophers are brought in by exclusively legume covers;
➣ Habitat for beneficial organisms;
➣ Improvements to soil quality; and
➣ Length of bloom and time of bloom to attract pollinators. Avoid pollinator competition from flowering
cover crops in crops with flowers that are less desirable to pollinators (i.e. pears).
Figure 22. This cover crop in a vineyard provides good habitat for beneficial insects and is aesthetically pleasing.
16
Appendix A. – Table 4. Cover Crop Interseeding Systems
Note: Only systems that cause negligible yield reduction have been included. All of these systems provide a cover which lives
through the winter or is winter-killed. All cover crops resist major damage during harvest of the cash crop unless otherwise noted.
Cover Crop
Cash Crop
Method
Benefits
Problems
Red clover, annual
or perennial
ryegrass i
Corn, late
sweet corn
Broadcast after last
cultivation ii
Good organic matter production;
N-fixation by red clover
Establishment may be poor in
a dry summer; annual
rye-grass may winter-kill
Rye iii
Corn, late
sweet corn
Broadcast in early
fall at 3 bu/acre
Reasonable establishment most
Stand may be patchy; stand
may be poor if the fall is dry
Red clover, alsike
Winter wheat,
clover, alfalfa,
spelt
yellow sweet clover
Sow on frozen
ground in early
spring
Good organic matter production
and N-fixation before next spring
crop
Ground may not freeze
sufficiently to support tractor
Bell bean iv
Fall brassicas
Plant two rows of
bell bean between
crop rows after last
cultivation
N-fixation for next crop; grows fast Expensive seed; cover crop
and then winter-kills; upright
will be damaged at harvest
growth does not interfere with crop
Annual rye-grass
Tomato,
pepper
Broadcast after last
cultivation ii
Good dry matter production by
next spring
May winter-kill
Hairy vetch
Late harvested
vegetables
Plant 1 or 2 rows
between rows of
vegetables after last
cultivation
N-fixation for next crop; no
interference with crop; spreads out
to give fair winter cover and good
spring production
May become a recurring weed
Rye
Late harvested
vegetables
Plant 1 or 2 rows
between rows of
vegetables after last
cultivation
Falls over to give fair winter cover;
no interference with crop
None apparent
Rye
Late harvested
vegetables
Broadcast at 2 to 3
bu/acre 3 to5 weeks
before harvest
Provides more uniform cover than
drilling between rows
Stand may be patchy; stand
may be poor if the fall is dry;
interferes with harvest of
short, leafy crops
Adapted from Mohler & Johnson, 2009.
i
Alfalfa, yellow sweetclover, crimson clover, birdsfoot trefoil, white clover, alsike clover and hairy vetch can also be established by
this method, but fall cover and spring dry matter production tend to be less than for red clover, annual ryegrass or perennial ryegrass.
ii
Seed can be applied at cultivation by attaching a forage seeder box to dribble seed onto the ground behind the cultivator tools. It
can also be spun on with an attachment or by hand. Seeding should be completed before the first rain after cultivation.
iii
Rye is the only cover crop that usually establishes well when surface sown in the fall. Spelt and annual ryegrass also have a
reasonable chance of success. Other surface seeded cover crops usually either fail to germinate or are heavily consumed by seed and
seedling feeding insects (species that are normally considered beneficials due to their consumption of weed seeds and pest insects).
iv
Bell bean is a small-seeded variety of fava bean. It is preferred over field pea in this application because it does not fall over or twine
into the crop.
17
Appendix B. – References
Barney, D.L. 2012. Storey’s Guide to Growing Organic Orchard Fruits. Storey Publishing, North Adams,
MA. 543 p.
Bentrup, G. 2008. Conservation Buffers: Design guidelines for buffers, corridors, and greenways. Gen. Tech.
Rep. SRS-109. Asheville, NC. Department of Agriculture, Forest Service, Southern Research Station. 110 p.
www.unl.edu/nac/bufferguidelines/docs/ conservation_buffers.pdf
Brennan, E. and N. Boyd. 2012. Winter Cover Crop Seeding Rate and Variety Affects during 8 Years of
Organic Vegetables 1. Cover Crop Biomass Production. Agronomy Journal. 104:684-698.
www.ars.usda.gov/research/publications/publications.htm?seq_no_115=273528
Brennan, E.B. and Smith, R.F., 2005. Winter Cover Crop Growth and Weed Suppression on the Central
Coast of California. Weed Technol. 19:1017-1024
Brennan, E.B., Daugovish, O., Smith, R.F., and Fennimore, S.A., 2011. Weeds, p. 43-46. In: Smith, R. F.,
Bugg, R. L., Daugovish, O., Gaskell, M., and Van Horn, M. (eds.), Cover cropping for vegetable production:
A grower’s handbook. Univ. of California, Oakland, CA.
Brennan, E. 2013. Personal communication.
Clark (ed.). 2007. Managing cover crops profitably. 3rd ed. Sustainable Agriculture Network Handbook Series;
book 9. www.sare.org/Learning-Center/Books/Managing-Cover-Crops-Profitably-3rd-Edition
Curell, C. 2012. Overseeding cover crops can give farms another option for integrating them into their
rotation. Michigan State University Extension. http://msue.anr.msu.edu/news/overseeding_cover_crops
Elmore, C.L., J.J. Stapleton, C.E. Bell, and J.E. DeVay. 1997. Soil Solarization: A Nonpesticidal Method for
Controlling Diseases, Nematodes, and Weeds. U.C. Vegetable Research and Information Center. 17 p.
www.vric.ucdavis.edu/pdf/soil_solarization.pdf
Hargrove, W.L., ed. Cover crops for clean water. SWCS, 1991.
Magdoff, F. and H. van Es. Cover Crops. 2000. p. 87-96 in Building soils for better crops. 2nd ed. Sustainable
Agriculture Network Handbook Series; book 4. National Agriculture Library. Beltsville, MD.
McGourty, G., J. Nosera, S. Tylicki, and A. Toth. 2008. Self-reseeding Annual Legumes Evaluated as Cover
Crops for Untilled Vineyards. California Agriculture 62:191-194.
http://californiaagriculture.ucanr.org/landingpage. cfm?article=ca.v062n04p191&fulltext=yes
Mohler, C.L., and S. E. Johnson (eds). 2009. Crop Rotation on Organic Farms: A Planning Manual. SARE.
www.sare.org/Learning-Center/Books/Crop-Rotation- on-Organic-Farms
Pfost, D.L. 1993. No-till Drills. Univ. of Missouri. http://extension.missouri.edu/p/G1210
Reeves, D.W. 1994. Cover crops and erosion. p. 125-172 In J.L. Hatfield and B.A. Stewart (eds.) Crops Residue
Management. CRC Press, Boca Raton, FL.
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Oregon State University. Organic Fertilizer and Cover Crop Calculator.
http://smallfarms.oregonstate.edu/calculator
Salon, P.R. 2010. Diverse Cover Crop Mixes for Good Soil Health. USDA-NRCS. Big Flats Plant Materials
Center. Corning, NY. 9 p.
www.hort.cornell.edu/expo/proceedings/2012/ Cover%20Crops/Cover%20Crops%20Salon.pdf
Schonbeck, M.W. 1988. Cover Cropping and Green Manuring on Small Farms in New England and New
York: An Informal Survey. East Falmouth, MA. New Alchemy Research Report #10.
Schonbeck, M. 2011. Plant and Manage Cover Crops for Maximum Weed Suppression.
www.extension.org/pages/18525/plant-and-manage-cover-crops-for-maximum-weed-suppression
Stika, J. 2013. Cover Crop Mixes: Getting the Crop You Want. Webinar. www.conservationwebinars.net
Sullivan, D.M., and N.D. Andrews. 2012. Estimating Plant-Available Nitrogen Release from Cover Crops.
A Pacific Northwest Publication. 23 p.
Sullivan, P. 2003. Overview of Cover Crops and Green Manures: Fundamentals of Sustainable Agriculture.
ATTR A, pub. no. IP024. http://attra.ncat.org/attra-pub/covercrop.html
Teasdale, J.R., 1996. Contribution of cover crops to weed management in sustainable agricultural systems.
J. Prod. Agric. 9:475-479.
Treadwell, D., N. Creamer, and K. Baldwin. 2010. An Introduction to Cover Crop Species for Organic
Farming Systems.
www.extension.org/pages/18542/an-introduction-to-cover-crop-species-for-organic-farming-systems
Treadwell, D., W. Klassen and M. Alligood. 2008. Annual Cover Crops in Florida Vegetable Systems Part 2:
Production. Florida Cooperative Extension Service, pub. no. HS1141. http://edis.ifas.ufl.edu/ document_hs389
Vaughan, Mace. Draft 2012. Conservation Cover (327) for Pollinators: Installation Guide and Job Sheet,
Western Oregon and Washington. Xerces Society for Invertebrate Conservation.
Vaughan, M., E. Mader, J. Guisse, J. Goldenetz-Dollar, and B. Borders. 2012. Conservation Cover (327) for
Pollinators in California’s Central Valley: Job Sheet Implementation Guide. Xerces Society for Invertebrate
Conservation.
Vaughan, M., E. Mader, J. Guisse, J. Goldenetz-Dollar, and B. Borders. 2012. Hedgerow Planting (422) for
Pollinators. Western Oregon & Washington Installation Guide and Job Sheet. Xerces Society for Invertebrate
Conservation.
Webber III, C.L., J.W. Schrefler, L.P. Brandenberger, W.C. Johnson III, A.R. Davis, M.J. Taylor, and R.A.
Boydston. 2008. Current Substances for Organic Weed Control in Vegetables or What Do We Have in Our
Organic Weed Control Toolbox? http://naldc.nal.usda.gov/download/45465/PDF
Xerces Society Pollinator Program, Seed Mix Calculator. Develop your own pollinator conservation seed mix
using this seed rate calculator.
www.xerces.org/wp-content/uploads/2009/11/XERCES-SEED-MIX-CALCULATOR.xls
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Resources
Conservation Buffers in Organic Systems Implementation Guide is a companion resource to this guide. It
includes a discussion of relevant NOP regulations, organic management practices, and technical guidance for
NRCS practice design in an organic context.
http://tilth.org/education-research/organic-conservation-program/wsare-project
Cover Crops and Soil Health is a NRCS resource which includes cover crop plant guides and other resources.
http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/plantsanimals/plants/projects/?cid=stelprdb1077238
Organic No-Till Farming is a Rodale Institute book by Jeff Moyer that describes a system that limits or
eliminates tillage and focuses on cover crops as a source of fertility and weed management.
http://rodaleinstitute.org/shop/organic-no-till-farming/
www.eOrganic.info is an online resource for organic research and outreach. The site hosts a range of resources on
cover crops including profiles of various crops, the use of cover crops for weed and disease management and more.
http://www.extension.org/pages/59454/cover-cropping-in-organic-farming-systems
20
Northwest
PDF
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