COVER CROPS FOR NEW AMERICAN CROPPING SYSTEMS

Seth Dabney

USDA-ARS

National Sedimentation Laboratoryseth.dabney@ars.usda.gov

Organization

Introduction: why cover crops (and no-till)? Concepts and Terms Cover Crop Management (killing cover

crops) Cover Crop Selection Cover Crop Resources

Why Grow Cover Crops?

Soil Management Water Management Pest Management Nutrient Management

Winter rye cover crop reduced runoff throughout yearaverage of 10 years and in three vegetable crop systems

Freehold loamy sand, 3% slope, New Jersey

No cover

Brill and Neal. 1950. Agron. J. 42:192-195.

Rye cover

Cover crops, high-residue crops, and no-till management can reduce runoff (and erosion even more!)

average of 6 years, Grenada silt loam, 5% slope, Mississippi

Reduced winter runoff with cover crops is mainly due to increased transpiration (and biomass production).

Meyer et al. 1999. Trans. ASAE 42:1645-1652.

Insufficient Residue = Soil Crusts(no-till won’t work with bare soil)

Cover crop residue mulch increases infiltration

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20 40 60 80 100

Days After Planting on 16 May 1984

So

il W

ate

r S

uc

tio

n (

J/k

g)

No-tillNo Cover Crop

No-tillCover Crop

Conventional-tillNo Cover Crop

SprinklerIrrigationtrigger

Sprinkler-irrigated rice on Crowley silt loam

Dabney (1998) J. Soil and Water Cons. 53(3):207-213

Why Grow Cover Crops?

Soil Management Water Management Pest Management Nutrient Management

Weed suppression in no-till corn by sub clover (background is conventional tillage, no cover)

Stripped cover crops of rye and a clover mix in Georgia for beneficial insect habitat.

Cotton was planted into the killed strips of rye while the clover was left growing until an application of Roundup at the 4 to 6 leaf stage

Photo: Harry Schomberg

Why Grow Cover Crops?

Soil Management Water Management Pest Management Nutrient Management

N managementconcepts and terms green manure: cover crops grown mainly to

improve the nutrition of subsequent main crops; may contain legumes that can add N to the cropping system

catch crop: cover crops grown to catch available N in the soil and thereby prevent leaching losses of N already in a cropping system

pre-emptive competition: uptake of soil nitrate by cover crops that would not have been lost to subsequent crops by leaching, thereby reducing availability of N to the subsequent crop

Concepts and terms

To be most effective, green manure crops should winter kill, be grazed, or be killed early in the spring to prevent pre-emptive competition and so that green manure N can be rapidly mineralized.

To be most effective, catch crops should be planted early in the fall to maximize root growth and N uptake.

High residue cover crops can increase yield potential and build soil C, but may also increase the economically optimal fertilizer N rate.

Catch crop effectiveness is highly correlated with rooting depth, but not with root densityWith warm weather, broad leaf plants may root more deeply more quickly than grasses

Thorup-Kristensen, K. 2001. Plant and Soil 230: 185–195.

(Crews and Peoples. 2005. Nutrient Cycling in Agroecosystems 72:101-120.)

Synchrony – temporal match between N supply and demand

Rice and legume cover crops:no-till improves synchrony

Source: Dabney et al. 1989. Agron J. 81:483-487

Harper et al. 1995. Crop Sci. 35:176-182.

Reseeding crimson clover biomass and N accumulation in GA

Sampling (of above ground biomass, litter, or roots) indicates net growth, not gross biomass production or N uptake

In reseeding legume systems, seed may contain ~ 50 kg N/ha

Plowing cover crops into soil does not increase soil organic matter Tillage controls weeds, loosens soil, and

smoothes fields burns up soil organic matter speeds organic N mineralization and

nitrification

Cover crops make no-till more successful (make no-till vegetables possible)

No-till with cover crops increases soil C

Worried about ammonia loss from no-till residues?

Even when hay is rained on, total NH3 losses to the atmosphere are minor

No-till with cover crops

0 1 2 3 4 5 6-600

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Time in Tillage System (yr)

Yie

ld -

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nv

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No-till **

Minimum-till **

Ridge-till (NS)

Triplett, Dabney, and Siefker. 1996 Agron. J. 88:507-512.

Cotton Yields Increased with Time in No-till

wheat cover

Dabney, Delgado, and Reeves. 1991. Comm. in Soil Sci. and Plant Anal. 32:1221-1250.

Cover crop residue mulch increases soil temperature

Improved early season cotton growth and survival with no-till

mycorrhiza hyphal counts per mm2

Why Not Grow Cover Crops?

Time Cost Lack of water Stand problems

Seed placement Pest and disease risks

10 ton biomass yield in California~50 mm (2 inches) of water per ton of cover crop biomass

Photo: Jeff Mitchell; Rolling rye cover crop, T & D Willey Farms, Madera, CA, April 21, 2006

Rhizoctonia infection of sorghum seedlings grown in soil with and without cover crop residues

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0 7 14 21 280.0

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1.00-3 cm plus residue

0-3 cm no residue

3-8 cm no residue

Dabney, Schrieber, Rothrock and Johnson. 1996. Agron. J. 88(6):961-970.

No-till planter: coulter to cut residues; double-disk opener set slightly deeper to plant into firm soil

Enhanced no-till planter: Tined-wheel row cleaner, scalloped double-disk openers reduce “hair-pinning” and tined press wheels close no-till seed slot without compaction.

Row cleaners can clear heavy residues,improving stands of direct seeded crops

Cover Crop Management(Killing Cover Crops without Tillage)

Spray (works best early) Mechanical (works best late)

Mow (flail gives most uniform residue distribution)

Undercut Roll (roll chop, knife roll)

Mowing – flail mowers leave residues evenly distributed, but operation and maintenance costs are high.

Undercutter (Nancy Creamer, NC State)

South AmericanKnife-rollers

American Rollers, Roll-choppers,and Roll crimpers

GA farmer, Lamar Black, rolls a 2 meter tall rye cover crop prior to planting corn or cotton

The resulting mulch suppresses weeds, conserves water, and lowers peak soil temperature.

Cover Crop Management (killing cover crops)

Direct seed no-till pumpkin into rye cover crop in Southwest VA (Ron Morse)

No-till transplanting cabbage into rolled rye, Hillsville, VA (Ron Morse)

Percent kill of summer cover crops in North Carolina (Creamer and Dabney, 2002, Am J. Alt. Ag. 17:32-40)

Cover crop Growth stage Mow UndercutRoll

(smooth)

Cowpea Vegetative 98 85 5

Soybean Early bloom 100 99 12

Buckwheat Mature 100 100 100

Pearl Millet Heading 0 73 18

German Millet Green Seed 100 100 100

Sorghum-sudangrass

Mature 0 89 25

German or Foxtail Millet(Setaria italica)

Mowed or Rolled

doesn’t re-grow

No-till no-herbicide broccoli transplanted into rolled foxtail millet (Ron Morse)

Weed control lasts longer after rolling than after mowing.

Sunn Hemp – Crotalaria juncea rapid legume growth following corn in Alabamakilled by frost ($2.5/lb from http://desertsunmarketing.com/)

Sunflowers grow fast, has wildlife benefits, and can be killed by rolling; mulch degrades quickly

Cover Crop Selections for the mid-South (humid zones 6+)

Winter Hairy Vetch

(Vicia villosa) Balansa clover

(Trifolium michelianum)‘Paradana’ or ‘Frontier’

Rye (Secale cereal)‘Abruzzi’ or ‘Merced’

Oat (Avena sativa)

Summer Cowpea

(Vigna unguiculata) Sunn hemp

(Crotalaria juncea) Foxtail millet

(Setaria italica) Sunflower

(Helianthus annus) Forage turnip

• (Brassica rapa) Forage radish

• (Raphanus sativus)

Cover Crop Evaluation Sites

0 to -56B

Nursery evaluations of hardiness and reseeding abilityOn-farm testing of management alternatives.

20 to 15

15 to 10

5 to 0

10 to 5

ZoneMean Annual

Minimum Fo

7A

7B

8A

8B

Balansa cloverTrifolium michelianum Savi – a superior reseeding winter cover crop

Tiptonville, TN 6B

Mississippi County, AR 7A

Moorhead, MS 8A

Cover Crop Evaluation Sites

0 to -56B

Nursery evaluations of hardiness and reseeding abilityOn-farm testing of management alternatives.

20 to 15

15 to 10

5 to 0

10 to 5

ZoneMean Annual

Minimum Fo

7A

7B

8A

8B

On-farm reseeding demonstration/adoption

Thighman Lake

Seed size: 1000 to 1400 per gramPlant 5 lb/a (8 if coated); ~$2.00/lbKamprath Seed (800-466-9959), Manteca, CA

Rye, Balansa, or No cover(Average of NT and RT) silty clay soil, Stoneville, MS

NC Rye Clover

Kg N/ha

2001 140 140 140

2002 112 134 45

2003 112 134 45

2004 157 179 90

Locke et al. (unpublished)

NT with rye was most profitable over four years

N Fertilizer Applied

Sweet Potato

Rodale Roller at DCDC, Metcalf, MS, in 2006part of a Conservation Innovation Grant

Things that went wrong:

Rye Stand Marginal (Rita)

Rye too old (roller delivered late)

Soil too dry

Planter depth set too shallow (poor cotton stand)

Needed herbicide (thin mulch, poor stand), but herbicide was caught on mulch (poor weed control)

Fertilizer N not increased (pre-emptive competition)

Result: poor stand, poor growth, poor weed control, poor yield

Let cover crops grow longer (only if water is available)

increased residue can be managed Increased residues control weeds increased residue conserves water later maintains mycorrhiza hyphae network for early

growth boost

Do not till needlessly it is like taking money out of the bank!

Conclusions: Cover Crop Opportunities

Catch crop or green manure Synchrony (i.e. N recovery in no-till rice) Balansa clover as a reseeding legume Cover crops for bio-fuel production fields in

humid zones 6+ (available water and sunlight) Research to identify insect/disease complex

when planting crops other than rice into recently killed legume cover crops

Selected resources on the web ATTRA

http://attra.ncat.org/attra-pub/covercrop.html NAL/SAN

http://www.sare.org/publications/covercrops/covercrops.pdf ARS

http://www.ars.usda.gov/is/np/tomatoes.html California

http://www.sarep.ucdavis.edu/ccrop/ Michigan

http://www.covercrops.msu.edu Cedar Meadow (Steve Groff)

http://www.cedarmeadowfarm.com/ Rolf Derpsch

http://www.rolf-derpsch.com/

Questions?

Rolf Derpsch uses rolled black oat cover crop residues to make no-till successful in Paraguay