COVER CROPS FOR NEW AMERICAN CROPPING SYSTEMS

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COVER CROPS FOR NEW AMERICAN CROPPING SYSTEMS

• Seth Dabney
• USDA-ARS
• National Sedimentation Laboratoryseth.dabney_at_ars.
  usda.gov

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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 systemsFreehold loamy sand, 3 slope, New
Jersey
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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 421645-1652.
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Insufficient Residue Soil Crusts(no-till wont
work with bare soil)
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Cover crop residue mulch increases infiltration
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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
185195.
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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
185195.
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Synchrony temporal match between N supply and
demand
(Crews and Peoples. 2005. Nutrient Cycling in
Agroecosystems 72101-120.)
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Rice and legume cover cropsno-till improves
synchrony
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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
Harper et al. 1995. Crop Sci. 35176-182.
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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
Harper et al. 1995. Crop Sci. 35176-182.
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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
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Cover crop residue mulch increases soil
temperature
Dabney, Delgado, and Reeves. 1991. Comm. in Soil
Sci. and Plant Anal. 321221-1250.
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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 California50 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
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. 1732-40)
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German or Foxtail Millet(Setaria italica)

• Mowed or Rolled
• doesnt 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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Balansa cloverTrifolium michelianum Savi a
superior reseeding winter cover crop
Mississippi County, AR 7A
Moorhead, MS 8A
Tiptonville, TN 6B
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On-farm reseeding demonstration/adoption
Thighman Lake
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Seed size 1000 to 1400 per gram Plant 5 lb/a (8
if coated) 2.00/lb Kamprath 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
N Fertilizer Applied
Locke et al. (unpublished) NT with rye was most
profitable over four years
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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/coverc
  rops.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
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Why Grow Cover Crops?

• Increase yield (nutrients, mycorrhiza, water)
• Build up soil carbon
• Decrease runoff and erosion (wind and water)
• Reduce N leaching
• Decrease weed growth
• (Cover crops must be easy to control or they
  could become weeds)
• Increase beneficial insects