Transcript COVER CROPS FOR NEW AMERICAN CROPPING SYSTEMS Seth Dabney USDA-ARS National Sedimentation Laboratory [email protected] Organization      Introduction: why cover crops (and no-till)? Concepts and Terms Cover Crop Management (killing.

COVER CROPS FOR NEW
AMERICAN CROPPING SYSTEMS
Seth Dabney
USDA-ARS
National Sedimentation Laboratory
[email protected]
Organization
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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?
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Soil Management
Water Management
Pest Management
Nutrient Management
Winter rye cover crop reduced runoff throughout year
average 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
Sprinkler-irrigated rice on Crowley silt loam
Soil Water Suction (J/kg)
90
Conventional-till
No Cover Crop
80
70
No-till
No Cover Crop
60
50
Sprinkler
Irrigation
trigger
40
30
20
10
No-till
Cover Crop
0
20
40
60
80
100
Days After Planting on 16 May 1984
Dabney (1998) J. Soil and Water Cons. 53(3):207-213
Why Grow Cover Crops?
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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?
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Soil Management
Water Management
Pest Management
Nutrient Management
N management
concepts and terms
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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
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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 density
With warm weather, broad leaf plants may root more
deeply more quickly than grasses
Thorup-Kristensen, K. 2001. Plant and Soil 230: 185–195.
Synchrony – temporal match
between N supply and demand
(Crews and Peoples. 2005. Nutrient Cycling in Agroecosystems 72:101-120.)
Rice and legume cover crops:
no-till improves synchrony
Source: Dabney et al. 1989. Agron J. 81:483-487
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
Harper et al. 1995. Crop Sci. 35:176-182.
Plowing cover crops into soil does
not increase soil organic matter
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Tillage controls weeds, loosens soil, and
smoothes fields
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Cover crops make no-till more successful
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burns up soil organic matter
speeds organic N mineralization and
nitrification
(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
wheat cover
Cover crop residue mulch increases soil temperature
Dabney, Delgado, and Reeves.
1991. Comm. in Soil Sci. and
Plant Anal. 32:1221-1250.
Improved early season cotton growth and
with
no-till
th survival
mycorrhiza
higher
wheat cover crop
2
ot mycorrhiza
mycorrhiz ahyphal
hyphalcounts
countsper
permm
mm2
2500
No-till soil
Conv.-till soil
2000
Conv.-till plant
0
No-till plant
500
Conv.-till plant
1000
No-till plant
1500
Why Not Grow Cover Crops?
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Time
Cost
Lack of water
Stand problems
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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
Fraction of Seedlings Infected
Rhizoctonia infection of sorghum seedlings grown in
soil with and without cover crop residues
1.0
0-3 cm plus residue
0.8
0-3 cm no residue
0.6
3-8 cm no residue
0.4
0.2
0.0
0
7
14
21
28
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)
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Spray (works best early)
Mechanical (works best late)
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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 American
Knife-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
Undercut
Roll
(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
Sorghumsudangrass
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 Alabama
killed 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+)
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Winter
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Hairy Vetch
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Summer
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(Vicia villosa)
Balansa clover
(Trifolium michelianum)
‘Paradana’ or ‘Frontier’
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Oat
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(Avena sativa)
(Helianthus annus)
Forage turnip
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(Setaria italica)
Sunflower
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(Crotalaria juncea)
Foxtail millet
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(Secale cereal)
‘Abruzzi’ or ‘Merced’
(Vigna unguiculata)
Sunn hemp
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Rye
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Cowpea
(Brassica rapa)
Forage radish
•
(Raphanus sativus)
Balansa clover
Trifolium michelianum Savi
– a superior reseeding winter cover crop
Mississippi County, AR 7A
Moorhead, MS 8A
Tiptonville, TN 6B
On-farm reseeding demonstration/adoption
Thighman
Lake
Seed size: 1000 to 1400 per gram
Plant 5 lb/a (8 if coated); ~$2.00/lb
Kamprath Seed (800-466-9959), Manteca, CA
Rye, Balansa, or No cover
(Average of NT and RT)
silty clay soil, Stoneville, MS
N Fertilizer Applied
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
Sweet
Potato
Rodale Roller at DCDC, Metcalf, MS, in 2006
part 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)
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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
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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
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ATTRA
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NAL/SAN
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http://attra.ncat.org/attra-pub/covercrop.html
http://www.sare.org/publications/covercrops/covercrops.pdf
ARS
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http://www.ars.usda.gov/is/np/tomatoes.html
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California
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http://www.sarep.ucdavis.edu/ccrop/
Michigan
 http://www.covercrops.msu.edu
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Cedar Meadow (Steve Groff)
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http://www.cedarmeadowfarm.com/
Rolf Derpsch
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http://www.rolf-derpsch.com/
Questions?
Rolf Derpsch uses rolled black oat cover crop residues to
make no-till successful in Paraguay