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

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

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

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

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

Fertility Management

Farming with Cover Crops

• Goal: Organic Matter– Grasses and everything else– Improve tilth and soil health

Abruzzi rye and Sudex: sorghum/sudan grass

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

Buckwheat Blooming

Syrphid Fly on Buckwheat

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

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

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

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

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

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

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

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

Examples of Biomass

Cereal rye7,000 lbs/ac

Sunn hemp 11,100 lbs/ac

Cowpeas 4,420 lbs/ac

Percent Cover

Oats/Austrian Winter Peas planted Oct 1, 2013

Oats/Austrian Winter Pea planted Sept 1, 2013

Photos taken Feb 2, 2014

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

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

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?

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

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

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

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

Growth Stage and C:N

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

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

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

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

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

Quadrats

4 square feet

1 square feet

Need Dry Biomass

• Spread cover crop out on tarp in the sun• Dry till “crispy”• Weigh again

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

Current Resources• Availability during growing season,

divide N by 2

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

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

Current ResourcesOregon State – Estimating PAN release from cover crops & OSU Organic Fertilizer and Cover Crop Calculator

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

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

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

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

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

The University of Georgia

Crop & Soil Science Dept.

College of Agricultural and Environmental Sciences

Sustainable Agriculture Program

www.SustainAgGA.org