Cover Crop Selection and Management

Molly HamiltonExtension Assistant

NC State University, Crop Science Department

Why use cover crops?

Why use cover crops?

• Fertility– N-fixing legumes

How much N can a legume fix?• Fix N over spring, reaching peak at full flower

Cover Crop Average N content %N in biomass

Maturity

Subterranean Clover 30-80 lb/acre 2 Mid-April

Crimson Clover 100-150 lb/acre 2.5 Late April

Austrian Winter Pea 100-150 lb/acre 3.5 Early May

Hairy Vetch 150-200 lb/acre 4 Early May

Berseem Clover 100-140 lb/acre 3 Late May

Common Vetch 120-170 lb/acre 3.5 Late MayNitrogen contents of several winter annual legume cover crops in 2009 and 2010 in NC. Ranges are approximate and will vary from year to year.

Courtesy of Dr. Julie Grossman, NCSU Soil Science

Why use cover crops?

• Fertility• Weed suppression– Out compete weeds– Leaf canopy that suppresses germination– Allelopathy

Why use cover crops? Weed Suppression

• Seed at high rates• Don’t let the cover become

a weed.• “Allelopathy is rarely

amazing”

Why use cover crops?

• Fertility• Weed suppression• Improve soil– Water infiltration– Relieve compaction– Improve soil tilth– Increase biology– Enhance nutrient cycling– Improve soil moisture– Improve water holding capacity

Why use cover crops? Organic Matter Add

organic matter

Increasebiological

activity(& diversity?)

Decomposition

Nutrients released

Aggregationincreased

Pore structureimproved

Humus formed

May reducesoil-borne disease

Improved tilth

HEALTHY PLANTSCourtesy of Chris Reberg-Horton

Why use cover crops?

• Fertility• Weed suppression• Improve soil• Reduce erosion

Selecting Cover Crops

What are your needs?Timing?

Location?Rotation?

Selecting Cover CropsWinter annual Non-legumes

WheatBarleyOatsRye

Triticale

Winter annualLegumes

Austrian Winter PeaCrimson clover

Hairy vetchBerseem clover

Subterranean clover

Summer annualNon-legumes

BuckwheatSorghum-Sudangrass

MilletSunflowers

Summer annualLegumes

CowpeasSoybeansSunhemp

Velvetbean

Small Grains: barley, oats, wheat, triticale

• Winter annual grasses (cereal grains)• Scavenge nutrients• Add organic matter• Suppress weeds• Can be grazed• Can be companion planted with legumes

Barley, Oats, Wheat, TriticaleManagement

• Plant in fall• Around 100 #/acre for thick cover – (1/4 # per 100 sq ft)

• Fertility needs are moderate• To kill: – Mow, scythe, or roll-kill at milk to soft dough stages

of kernel formation (spring)– Mow and till (winter or spring)– Till (winter)– Oats may winter kill

Oats

Rye (Secale cereale)

• Winter annual grass• Nutrient catch crop• Large amount of organic matter• Very competitive with weeds• Good companion crop• Can graze• Inexpensive• Very cold tolerant• Earlier maturing than other grass cover crops

RyeManagement

• Plant in fall• Moderate fertility needs• About 100 #/acre (1/4 # per 100 ft2)or 30-50

#/acre if planting with a legume• To kill:– Till (plow/disc) in winter or early spring– Mow, scyth, or roll-kill when full flower or into

milk-stage (spring: May)

Management CautionsGrain Cover Crops

• Needs adequate fertility to produce biomass

• Can tie up nitrogen when decomposing

• Produce lots of biomass• They are grasses – consider when planning

rotations

Winter Annual: Brassicas• Mustards, forage turnip, forage radish, rape, canola• Characteristics: large taproot, varied cold hardiness,

rosettes in winter turn to large stalked plant in spring• Biofumigant• Sulfur may be needed• Don’t do great in sandy soils• Management:

– Seed 1 to 2 months before first frost at 5 to 15 lb/acre

(0.03 lb or ½ oz./100 ft2) ½ inch to ¼ inch deep– To kill – mow and disc

Winter Annual Legume: Austrian winter pea

• Also known as field pea (but not in the South)• High-N fixer (90-150 lb N/acre), lots of biomass,

cold hardy, viney growth, • Management:– Drill/plant about ¾ to 1 inch deep (broadcast not

recommended)– Plant in fall– 70-90 lb/acre (1/5 # per 100 ft2)

– Kill: Just after full-bloom • mow, disc, roll-kill, scythe

– Decomposes quickly– Use correct innoculant

Winter Annual Legumes: Hairy Vetch

• Characteristics: viney growth, high N-fixer, cold tolerant

• Management:– Seed at 20-30 lb/A (0.05 lb/100 ft2)– in fall (3/4 inch deep)– Use correct innoculant– To kill:• Mow and disc, roll-kill at early seed “set” stage

– Re-seeding/weed issues?

Winter Annual Legume: Crimson Clover• Characteristics: Good N fixer, good beneficial

insect/pollinator habitat, beautiful• Does not like wet feet• Matures slightly earlier• Management: – Use correct innoculant– 20-25 lb/acre (0.05 lb/100 ft2)planted in fall, ¼ to ½ inch

deep– To kill:

• Mow and disc• Mow or roll-kill at late bloom/early seed set

– Will re-seed

Other winter annual legumes (that will work in NC)

• Berseem clover• Subterranean clover• Woolypod vetch• Cahaba white vetch

Management Cautions for Winter Legumes

• Use correct innoculant– Nitragin Co., INTX microbials, Johnny’s Select

Seeds, Peaceful Valley Farms, etc.• Most N is in above ground biomass• Max N in plant at full-bloom• N is not readily available to subsequent crop

Summer Cover Crops?

Summer Annuals: Buckwheat

• Characteristics: fast growing, suppresses weeds, good pollinator habitat, effective nutrient scavenger

• Succulent plant decomposes quickly• May go to seed = weed problem in next crop• Management:– Frost-sensitive, likes cool weather– Plant ½ inch deep 30-90 lb/acre – 0.1 lb/100 ft2

– Kill by mowing or disking (1 week after flowering)• Can be frost killed (not reliable to prevent re-seeding)

Summer Annuals: Sorghum-sudangrass

• Cross between grain sorghum (milo) and sudangrass• Characteristics: grows well in hot/dry, large

biomass producer, suppresses weeds (allelopathic)• Management:

– Plant 1-1 ½ inches deep from late spring-midsummer at 45 lb/acre (0.06 lb/100 ft2)

– Can be mowed (or grazed)– Does well planted with viney legumes– To kill

• Mow and disc• Frost kill

– Will tie up N

Summer Annual: Millets• Grasses, companion planted, frost-killed• German (foxtail) (Setaria italica)

– 2-5 ft tall, small seeded– Plant mid-May-August at 25-30 lb/acre (0.06 lb/100ft2)– Avoid sandy soils

• Pearl or cattail (Pennisetum glaucum)– 4-12 ft tall and performs well in sandy soils– Plant late April-July at 5 to 15 lb/acre (0.02 lb/100ft2

– Harder to kill• Japanese (Enchinochloa frumentacea)

– 2-4 ft tall and quick maturing– Plant April to July at 20-25 lb/acre (0.05 lb/100ft2) – Avoid sandy soils

From Western Illinois State UniversityFrom Iowa State Univeristy

German (foxtail) Millet

Japanese MilletFrom Texas A&M University

Summer Annual: Sunflowers• Characteristics: Tall, weed suppressive, pretty• Management:– Plant in warm soils at 4-5 lb/acre (0.01 lb/100 ft2) ½ -

1 inch deep– Modest fertility needs– Variety selection: cheapest seed or whatever looks

pretty– To kill:

• Mow, disc• Frost-kill

Summer Annual Legume: Cowpeas• Also called black eyed, southern, crowder, and

field pea• Characteristics: can produce 90-100 lb N,

succulent, decomposes quickly, can be viney, need warm weather

• Management:– Plant 40-100 lb/acre (up to ¼ lb/100 ft2)– ‘Ironclay’ or ‘Red Ripper’ recommended– To kill:

• Mechanical means not reliable• Frost-killed

Summer Annual Legumes: Soybean

• Characteristics: 2-4 ft tall, bushy, inexpensive, high N-fixer, forage types available

• Management:– Plant 60-100 lb/acre (up to ¼ lb/100 ft2)when soil

warms– Plant late-maturing varieties (Group VI or later)– To kill:• Mow and disc• Frost-killed

Alternative Summer Annual Legumes• Velvetbean (Mucuna deeringiana)– Viney legume (good in combinations)– does well in sandy/poor soils

• Sunhemp (Crotalaria juncea)– Very tall, herbaceous annual that needs good

drainage– Recommended to plant after summer

crop (like corn) to grow in months up to first frost

• Seed for these plants is hard to find and can be expensive

CEFS, NC State University

CEFS, NC State University

Perennial Cover Crops• Paths, between rows (“living mulch”), forage/hay, long-term

planning• Options:

– Alfalfa: short-lived perennial• Can be mowed or grazed• Needs well-drained, near neutral soil• Seed in fall • Most susceptible to pests

– White clover (Trifolium repens): perennial• Seed in late summer/fall• Choose intermediate sizes (i.e. Dutch white)• Can be mowed, grazed, trafficked

– Red clover (Trifolium pratense): short-lived perennial• Mammoth red (can be cut once) or medium red (multi-cut)• Seed in fall • Kill mechanically when in bloom or dormant

Organic No-till?

Organic No-till• Winter annual cover crop is roll-killed• Cash crop planted into rolled cover • Need a lot of biomass (8,000 lb dry matter/A or over

18 lb/100 ft2)– Don’t attempt with poor or spotty stands

• Roll at full bloom or just beyond• Roller-crimper, cultipaker, scythe, mower, etc.• Need to get through cover crop mat to plant

Kill timing for legume cover crops MATURITY TIME SPECIES CULTIVAR

Early Mid-April none none

Mid Late-April/ Early May

Crimson clover AU Robin Dixie

AU Sunrise Tibbee

Late-April/ Early May

Hairy vetch AU Earlycover

Late Late-May Hairy vetch AU Merit Experimental USDA line

Winter hardy Earlycover Late-May Winter pea (unstated) and Whistler

Early June Common vetch (unstated)

Early June Berseem Clover Bigbee

Mid June Sweet clover Hubam

Hard-to-kill Sub clover Denmark

Not winter hardy Blue Lupine Tifblue 78

Courtesy of Chris Reberg-Horton, NCSU

Kill times for rye (Secale cereal) cover crops

MATURITY TIME CULTIVAR

Early Late April Wrens Abruzzi

Wrens 96

MatonII

Mid Early May Aroostook

Late Mid to late May

Rymin

Wheeler

Rules of thumb for planting in no-till

• Need to get through thick mat of rolled cover• Use straight edged no-till coulters. • Heavy duty downforce springs or a pneumatic

downforce system is often needed.• Some planter may need extra weight mounted on

the frame. • Cast iron and rolling spider closers are reported to

be the best choices. Even with the heaviest of closers, sealing the trench can be difficult at times.

How much N am I getting?• Nearly all N comes from above ground biomass• Material must decompose for crop to get N• About 50% of N will be available for next crop

(40% if residue left on surface)

Cover Crop Average N content %N in biomass

Maturity

Subterranean Clover 30-80 lb/acre 2 Mid-April

Crimson Clover 100-150 lb/acre 2.5 Late April

Austrian Winter Pea 100-150 lb/acre 3.5 Early May

Hairy Vetch 150-200 lb/acre 4 Early May

Berseem Clover 100-140 lb/acre 3 Late May

Common Vetch 120-170 lb/acre 3.5 Late MayNitrogen contents of several winter annual legume cover crops in 2009 and 2010 in NC. Ranges are approximate and will vary from year to year.

How much N am I getting?1. Determine biomass produced. – Use a frame of known dimensions, clip plants at

ground level, dry plants to crunchy dry– Calculate: • Area sampled: 2x2 = 4 sq.ft. x 2 (samples) = 8 sq.ft.

• Dried samples weigh 1.2 lbs.• 1.2 lbs/8 s.f. X 43,560 s.f./acre = 6,534 lbs dry biomass

2 ft

2 ft

2. Use tissue test or estimate %N in cover crop– Multiply dry biomass yield with % of Nitrogen

(6453 lbs/acre) x (0.035) = 226 lb of N in biomass

3. Predict how quickly biomass will decompose, releasing nutrients for crop– Multiply legume biomass nitrogen with :

• 0.50 if residue will be incorporated• 0.40 if residue is left on surface

– (226 lb N) x (0.50) = 113 lb N/acre available to cropCover Crop Average N content %N in

biomass

Maturity

Subterranean Clover 30-80 lb/acre 2 Mid-AprilCrimson Clover 100-150 lb/acre 2.5 Late AprilAustrian Winter Pea 100-150 lb/acre 3.5 Early MayHairy Vetch 150-200 lb/acre 4 Early MayBerseem Clover 100-140 lb/acre 3 Late MayCommon Vetch 120-170 lb/acre 3.5 Late MayNitrogen contents of several winter annual legume cover crops in 2009 and 2010 in NC. Ranges are approximate and will vary from year to year.

Seed Sources

• Local feed and seed• Southern States• Dirtworks.net• Improved Forages • Johnny’s Selected Seed• Albert Lea Seedhouse• Blue River Organic Hybrids• Welter Seed and Honey Co.

Innoculant Sources:– Nitragin Co., INTX microbials

Further resources• Bowman, G., C. Shirley, and C. Cramer. 1998. Managing Cover Crops Profitably. The

Sustainable Agriculture Network Handbook Series, Book 3. Available from Sustainable Agriculture Publications, Hills Building, Room 10, University of Vermont, Burlington, VT05405-0082. (http://www.sare.org/handbook/mccp2/index.htm)

• SAREP cover crop database: http://www.sarep.ucdavis.edu/database/covercrops • Hoyt, Wagger, Crozier. 2004. Soilfacts: Winter Annual Cover Crops (AGW-439-58);

www.soil.ncsu.edu/publications/Soilfacts/AGW-439-58/AGW_439_58.pdf • Creamer, Baldwin. 1999. Summer Cover Crops;

http://www.ces.ncsu.edu/hil/hil-37.html • Growing Small Farms: Cover crops for sustainable production:

growingsmallfarms.ces.ncsu.edu/growingsmallfarms-covcropindex/ • NCSU Organic Grain Program:

http://www.organicgrains.ncsu.edu/cropproduction/covercrops.htm• ATTRA: Overview of cover crops and green manures:

https://attra.ncat.org/attra-pub/summaries/summary.php?pub=288• Oregon SU Small Farm cover crop calculator:

http://smallfarms.oregonstate.edu/calculator• NCDA Plant Tissue Analysis (Agronomic Division):

www.ncagr.gov/agronomi/uyrplant.htm • NCSU Small Grains: www.smallgrains.ncsu.edu