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COVER CROPS FOR NEW AMERICAN CROPPING SYSTEMS
Seth Dabney
USDA-ARS
National Sedimentation [email protected]
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Organization
Introduction: why cover crops (and no-till)? Concepts and Terms Cover Crop Management (killing cover
crops) Cover Crop Selection Cover Crop Resources
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Why Grow Cover Crops?
Soil Management Water Management Pest Management Nutrient Management
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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
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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.
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Insufficient Residue = Soil Crusts(no-till won’t work with bare soil)
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Cover crop residue mulch increases infiltration
0
10
20
30
40
50
60
70
80
90
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
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Why Grow Cover Crops?
Soil Management Water Management Pest Management Nutrient Management
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Weed suppression in no-till corn by sub clover (background is conventional tillage, no cover)
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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
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Why Grow Cover Crops?
Soil Management Water Management Pest Management Nutrient Management
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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
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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.
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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.
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(Crews and Peoples. 2005. Nutrient Cycling in Agroecosystems 72:101-120.)
Synchrony – temporal match between N supply and demand
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Rice and legume cover crops:no-till improves synchrony
Source: Dabney et al. 1989. Agron J. 81:483-487
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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
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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
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Worried about ammonia loss from no-till residues?
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Even when hay is rained on, total NH3 losses to the atmosphere are minor
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No-till with cover crops
0 1 2 3 4 5 6-600
-400
-200
0
200
400
600
800
Time in Tillage System (yr)
Yie
ld -
Co
nv
en
tio
na
l (k
g/h
a)
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
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Dabney, Delgado, and Reeves. 1991. Comm. in Soil Sci. and Plant Anal. 32:1221-1250.
Cover crop residue mulch increases soil temperature
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Improved early season cotton growth and survival with no-till
mycorrhiza hyphal counts per mm2
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Why Not Grow Cover Crops?
Time Cost Lack of water Stand problems
Seed placement Pest and disease risks
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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
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Rhizoctonia infection of sorghum seedlings grown in soil with and without cover crop residues
Fra
ctio
n of
See
dlin
gs In
fect
ed
0 7 14 21 280.0
0.2
0.4
0.6
0.8
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.
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No-till planter: coulter to cut residues; double-disk opener set slightly deeper to plant into firm soil
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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.
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Row cleaners can clear heavy residues,improving stands of direct seeded crops
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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)
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Mowing – flail mowers leave residues evenly distributed, but operation and maintenance costs are high.
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Undercutter (Nancy Creamer, NC State)
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South AmericanKnife-rollers
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American Rollers, Roll-choppers,and Roll crimpers
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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.
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Cover Crop Management (killing cover crops)
Direct seed no-till pumpkin into rye cover crop in Southwest VA (Ron Morse)
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No-till transplanting cabbage into rolled rye, Hillsville, VA (Ron Morse)
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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
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German or Foxtail Millet(Setaria italica)
Mowed or Rolled
doesn’t re-grow
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No-till no-herbicide broccoli transplanted into rolled foxtail millet (Ron Morse)
Weed control lasts longer after rolling than after mowing.
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Sunn Hemp – Crotalaria juncea rapid legume growth following corn in Alabamakilled by frost ($2.5/lb from http://desertsunmarketing.com/)
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Sunflowers grow fast, has wildlife benefits, and can be killed by rolling; mulch degrades quickly
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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)
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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
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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
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On-farm reseeding demonstration/adoption
Thighman Lake
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Seed size: 1000 to 1400 per gramPlant 5 lb/a (8 if coated); ~$2.00/lbKamprath Seed (800-466-9959), Manteca, CA
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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
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Sweet Potato
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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
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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!
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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
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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/
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Questions?
Rolf Derpsch uses rolled black oat cover crop residues to make no-till successful in Paraguay