Download - Southern SAWG Cover Crops 2015
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Getting the Most from Cover Crops
Daniel ParsonFarmer/Educator
Oxford College FarmEmory University
Julia W. GaskinSustainable Agriculture CoordinatorCrop and Soil Science Department
College of Agricultural and Environmental SciencesUniversity of Georgia
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What Are Cover Crops?Crops grown primarily for soil or ecosystem improvement rather than cash
Cereal Rye
Winter Summer
Oats/Austrian Winter Peas
Sunn hemp
Buckwheat
Sorghum/Cowpeas
Rye/Crimson Clover
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Cover Crop Benefits• Prevents soil erosion • Increases soil quality• Prevents nutrient loss• Provides weed control• Creates habitat for beneficial insects• Suppresses diseases and nematodes• Provides nitrogen from legumes
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Farming with Cover Crops
• Establish planned crop rotations• Fit cover crops into winter, spring,
summer, fall• Establish your goals
– Soil fertility (N)– Organic matter– Beneficial insects– Weed suppression
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Farming with Cover Crops
• Goal: Soil Fertility (N)– Legume cover crops– Reduce outside fertility needs– Grow a good crop!
Crimson Clover, Hairy Vetch, Austrian Winter Pea, Cowpea, Soybean
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Fertility Management
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Farming with Cover Crops
• Goal: Organic Matter– Grasses and everything else– Improve tilth and soil health
Abruzzi rye and Sudex: sorghum/sudan grass
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Farming with Cover Crops
• Goal: Beneficial Insects– Buckwheat and other flowering plants– Relay-cropping of beneficial builders– Grasses over winter for alternative food
Buckwheat, clover, vetch, rye, oats, wheat and more
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Buckwheat Blooming
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Syrphid Fly on Buckwheat
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Farming with Cover Crops
• Goal: Weed suppression– Grow a good crop– Crop timing: before peak weed seed
emergence– Densely growing crop
Velvetbean, cowpea, rye, clover, oats
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Growing Good Cover Crops
• Timing of planting• Prepare the ground
– Minimal tillage– Enough tillage
• Spread the seed according to recommendations
• Cover if needed: final tillage pass
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Crimson Clover and Oats
• When: – Plant early-September– Plow in when needed or April
• How: – Cover oats, don’t cover clover– Plant before rain or irrigate
• Why: – Nitrogen, spring blooms– Early spring planting: oats can winter-kill
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Grain Rye and Austrian Pea
• When: September-December and beyond
• How: – Cover both at planting for better results– Cut back rye rate by 25-50%
• Why: – Nutrients (N) and organic matter– Beneficial insect habitat: prey
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Buckwheat
• When: last frost to weeks before first frost– Quick cover for fields – Relay plant for greatest effect
• Why: beneficial insect attractor• How: lightly cover seed, allow to reseed
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Cowpea/Soybean and Sudex
• When: summer for long-term cover• How: cover lightly at planting
– Mow Sudex at 40 inches– Add buckwheat for early cover—will
reseed!• Why: Nitrogen, OM, and soil tilth
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How Do you Maximize Benefits?
• Maintain healthy soil – maintain or build soil organic matter
• Keep soil covered• Pick cover crop to meet your goals• Maximize biomass!
– Timely planting and establishing a good stand
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Biomass Needed
• Maintain soil organic matter– 6,000 to 8,000 lbs/ac/yr
• Control weeds in current growing season– At least 30% cover by 4 weeks after planting
• Control weeds in following cash crop season– 7,000 to 8,000 lbs/ac
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Examples of Biomass
Cereal rye7,000 lbs/ac
Sunn hemp 11,100 lbs/ac
Cowpeas 4,420 lbs/ac
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Percent Cover
Oats/Austrian Winter Peas planted Oct 1, 2013
Oats/Austrian Winter Pea planted Sept 1, 2013
Photos taken Feb 2, 2014
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Cover Crop Residues (lbs/ac)
Winter• Cereal rye- 3,000 to 10,000 • Crimson clover – 3,500 to 5,500 • Tillage radish – 4,000 to 7,000
Summer• Sudan sorghum – 8,000 to 10,000 • Millet (German/Japanese) - ≈4,000 • Buckwheat – 2,000 to 4,000 -6 to 8 wks• Sunnhemp – 5,000 to 11,000• Cowpeas – 2,500 to 4,500
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Cover Crop MixturesGrain is tall; legume spreads underneath for weed suppression
Recommended rates2/3 legume to 1/3 grain½ legume to ½ grain
Growing conditions influence which species dominate.
High N favor grainsLow N favors legumes
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Problematic for Farmers
• Cover crops are an important nitrogen (N) source
• How much N can I expect?• When will it be released?• Is it profitable?
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Nitrogen in Cover Crop ResiduesWinter Legumes lb N / Acre
Alfalfa 100-250Crimson Clover 50-160
Austrian Winter Pea 40-175White Clover 75-140
Vetch 45-200Summer Legumes
Cowpeas 40-60Soybean 35-45
Sunn Hemp 20-280
Reeves, 1994; Mansoer et al, 1997; Schomberg et al. 2007 Gaskin unpublished data
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Nitrogen Release• All nitrogen in cover crop not available to next
crop• Example: Cowpeas followed by broccoli
– Total N in cowpeas = 168 lbs/ac– Estimated N supplied by cover crop 78 lbs/ac (46%)– Rule of thumb: Divide by 2
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Nitrogen Release
• Nitrogen not released till cover crop decomposed
• Soil temperature and moisture– Need warmer temperatures for microbes to work– Need soil moisture for microbes to work
• Too dry – no decomposition• Too wet – right microbes inhibited
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Nitrogen Release• Microbes get N first!!• Carbon to N ratio:
< 25 net mineralization (N released)Think green materials!
> 25 net immobilization (N not available)Think brown materials!
• Cover crop quality – lignin, tannins and polyphenols slow the rate of
decomposition
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Growth Stage and C:N
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Timing of N ReleaseCrimson Clover
0
20
40
60
80
100
0 50 100 150Days After Placing in the Field
% o
f Orig
inal
N R
emai
ning NT 1992
NT 1993NT 1985CT 1985
Quemada et al., 1997. Wilson & Hargrove, 1986
Nitrogen uptake by corn
Incorporated
On Surface
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Predicting N from Cover Crop
Minimum data set:• Biomass• N concentration in cover crop
Better data set:• Cover crop quality• Soil moisture and temperature• Initial soil conditions
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Biomass Is Critical!Crimson clover: 3% Nitrogen and 1,000 lbs/ac30 Lbs Nitrogen/acre
Crimson clover: 3% Nitrogen and 4,000 lbs/ac120 Lbs Nitrogen/acre
Crimson clover: 3% Nitrogen and 6,000 lbs/ac180 Lbs Nitrogen/acre
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Planting Date is Critical to High Biomass!!
Oats/Austrian Winter Peas planted Oct 1, 2013
Oats/Austrian Winter Pea planted Sept 1, 2013
This cover crop NEVER caught up. Only got 20 lbs nitrogen/ac
Photos taken Feb 2, 2014
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Cover Crop Sampling• Need aboveground biomass sample
– Use quadrat to sample known area• Clovers, smaller cover crops – 1 to 2ft2 quadrats, 3 to 4
samples• Larger or mixed species – 2 to 3 ft2 quadrats, 3 to 4
samples– Cut cover crop to soil surface– Record wet weight
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Quadrats
4 square feet
1 square feet
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Need Dry Biomass
• Spread cover crop out on tarp in the sun• Dry till “crispy”• Weigh again
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Current Resources
– Measure biomass– Legume rule of thumb:
• 3.5 to 4% N before flowering• 3 to 3.5% at flowering• Reduce by 1% for woody legumes
– Cereal grains rule of thumb:• 2 to 3 % before flowering• 1.5 to 2.5% after flowering
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Current Resources• Availability during growing season,
divide N by 2
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Cover Crop Sample Submission
• Fresh biomass sample submission– Put fresh quadrat samples on clean tarp– Mix THOROUGHLY
• Tearing up large plants parts if need be
Photo Dr. Dan Sullivan, OSU
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Cover Crop Sample Submission
• Mound sample up into cone
• Divide into 4
• Keep 2 subsamples• Repeat if necessary• Put representative sample in 1 gallon plastic bag
– Ship with blue ice to keep it cool• Request N and percent moisture analysis
Keep
Keep
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Current ResourcesOregon State – Estimating PAN release from cover crops & OSU Organic Fertilizer and Cover Crop Calculator
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Biomass – 6,372 lbs/acCover crop N – 2.64%
N Prediction Model
Total N = 168 lbs/ac30% available
Yields 28% greater than county average
Rec N = 120 lbs/acCC Cred = 90 lbs/acApplied = 30 lbs/ac
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Caution – High biomass cereal grain cover crops can immobilize N
Biomass – 15,859 lbs/acCover crop N – 1.06%
Yields only 38% county average
Total N = 168 lbs/ac0% available
Rec N = 90 lbs/acCC Cred = 45 lbs/acApplied = 54 lbs/ac
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Taking It to the Farm!
Average Yield Cover Crop 0 N = 5,179 lbs/acAverage Yield Cover Crop 1x N = 6,498 lbs/acAverage Yield No Cover 1x N = 5,467 lbs/ac
Funding by: NRCS National Conservation Innovation Grant
Cowpeas followed by broccoliOne time harvest
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Taking It to the Farm 2!
Cover crop 0 N = 1,803 lbs/acCover Crop 1N = 2,850 lbs/acNo cover 1 N = 3,458 lbs/ac
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Cover Crop Resources• www.SustainAgGA.org. Click on Resources on lefthand side• Managing Cover Crops Profitably, 2nd ed. Sustainable
Agriculture Network. www.sare.org/publications/covercrops/covercrops.pdf
• Sustainable Practices for Vegetable Production in the South www.cals.ncsu.edu/sustainable/peet/ index.html
• National Sustainable Agriculture Information Service (ATTRA) www.attra.org
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The University of Georgia
Crop & Soil Science Dept.
College of Agricultural and Environmental Sciences
Sustainable Agriculture Program
www.SustainAgGA.org
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