crop rotationsHistorically

revolved around LEGUMES

Cover crops

less

Adapted from Sarrantonio (1994)

Broccoli Lettuce

Finding the right times to fit in cover crops

Summer Fallow

Spring Summer Fall

= cover crop

A = cover crop seeded after spring crop harvested, tilled in before fall cropB = cover crop overseeded into spring crop, tilled in before fall cropC = Cover crop allowed to grow in strips when fall crop is young

A

B

C

Wisconsin Integrated Cropping Systems Trial.

1 Gross margins are calculated by taking the gross revenue per acre (yield times price at harvest) minus variable costs of production (seed, fertilizer, pesticides, drying costs, fuel, and repairs).

Wisconsin Integrated Cropping Systems Trial.

CS1 = continuous corn CS2 = corn/soybean CS3 = corn/soybean/wheatCS4 = 1 year corn/3 years alfalfa CS5 = corn/alfalfa/alfalfa-oats-peas

Wisconsin Integrated Cropping Systems Trial

Energy relationships

High energy cost of N fertilizer

Why is the net energy gain for ethanol (~ 1.2) so much lower than all of these ?

Highest energy

input and output

Lowest output:input

ratio

How much N can frost seeded red clover fix ??

Red clover frost seeded into winter wheat. 

Seed is broadcast onto frozen and cracked soil in mid-March after snow melt.  Seedlings remain relatively small until wheat harvest, at which time they have full sunlight and three months to grow and fix atmospheric nitrogen.  Total nitrogen accumulation typically exceeds 100 lbs./a

by the end of the growing season. 

Hairy vetch can be successfully planted after wheat harvest. On the two occasions (out of 18 site-years

of the WICST trial) when the red clover failed to establish well, the vetch produced an average of

115 lbs./a of nitrogen, providing an excellent “back-up plan” that reduces one of the potential risks of

relying on a companion-seeded cover crop for nitrogen.  Late July vetch plantings can be riskier

than frost seeding clover.

Cover crops can be managed economically ! 

When the cost of purchased nitrogen is low, the value of the nitrogen alone does not usually justify the cost of a legume. 

However, other benefits such as reduced herbicide use, improved yield of other crops, reduced nitrate leaching, improved soil structure, diminished erosion and reduced

fossil fuel use make cover crops more attractive. As energy prices increase, cover crops become increasingly more

attractive.

Cover crops can provide most or all of the nitrogen required by corn growth. 

WI trials to determine whether supplemental nitrogen was worthwhile found that additional nitrogen (either starter or sidedressed) produced a significant yield

increase only about one-fourth of the time.  The exceptions always occurred during years with cool

springs, when there is a slow release of legume nitrogen. 

WICST scientists recommend that producers perform the pre-sidedress nitrate test when

cover crop growth is modest or spring weather is particularly cool, and use recommended

rates of sidedress N accordingly.  (When justified, sidedress N was more

economic than starter N.)

Use supplemental N to balance the budget

Total N uptake Cover crop N

Crop residue N

Soil N

N credits

supplementalNN

Compost/Manure N

Many vegetable crop residues are comparable to a legume cover crop

http://res2.agr.ca/stjean/publication/bulletin/nitrogen-azote_e.pdf

Residues with a low C:N ratio that decompose quickly can release N even though they are not legumes

http://talk.newagtalk.com/forums/thread-view.asp?tid=73097&mid=521773#M521773

We've done some PSNT tests with and w/o fall seeded radish. Kind of a moving target (year to year) in N credits, but I will say that we've always had a bigger credit following radish than what we had without. That could be for a lot reasons. Weather, soil types, temp, etc. I've had an increase of almost 80#s of N using radish vs none, and I've had an increase of 20# vs none.

N credit is a very nice benefit of using a cover like radish, but I also like the other benefits from radish we've observed. Trouble with cover crops is putting a $ benefit on many of them. I can hardly ever say that if I spend 10 bucks on a particular cover, it'll for sure give me 20 back next year. In the big picture, I feel that if looked at over say a 5 or 10 year period, we've put more money in the bank by using covers than we've spent. I don't know how to quantify things $ wise like the value of increased OM, for example.

Pat Sheridan (Fairgrove, Michigan)

LocationCover Crop

Grain Crop

0 lb N/ac

60 lb N/ac

180 lb N/ac

240 lb N/ac

HortinHairy Vetch

Corn 169 184 180 184

Hortin Fallow Corn 105 142 162 164

Hortin Rye Corn 65 102 119 120

HortinHairy Vetch

Sorghum 90 97 99 100

Hortin Fallow Sorghum 74 87 94 92

Hortin Rye Sorghum 54 72 77 74

http://frec.cropsci.uiuc.edu/1993/report13/table10.htm

U of I on-farm covercrop research(grain yields = bu/acre)

Cereal rye often suppresses corn and sorghum yields

Impact of hairy vetch and rye cover crops on corn yield in IL

More crop residues = more OM

CC

CC

20 years of similar tillage intensity and C inputsbut contrasting types of organic inputs

Crop residuesCover Crops

Animal manure

Crop residues

Understanding cover crops as nutrient sources

Early kill date = 114 lbs total N

Late kill date = 140 lbs total N

Wagger (1989)

50% N

Late kill date = 131 lbs total N

Early kill date = 107 lbs total N

2 wks<4 wks

http://www.ars.usda.gov/is/pr/2004/041126.htm

Timing of establishment and termination of legume cover crops strongly influences their contribution of N to subsequent crops

Early planting and late termination (after bloom begins) normally maximizes N contribution to subsequent crops

in the sprin

g

AC Greenfix was the top N fixer in a recent studylb

s of

N /

acr

e

DO NOT PLANT AC GREENFIX WHERE SOYBEANS WERE GROWN THE YEAR BEFORE

- AC GREENFIX WILL NOT DO WELL!

Like most legumes, AC Greenfix grows slowly for the first 30-40 days.

Weeds can be controlled by mowing or grazing when AC

Greenfix starts to flower or during the first week of flowering. This will make the AC Greenfix tiller out faster and grow

faster, resulting in a better stand.

For maximum nitrogen availability to the following crop, the plants should be incorporated before seedpods begin to filling.

Important considerations

Is the N fixed by AC Greenfix

free ?

Seed cost ~ $40/acrePlanting cost ~ $20/acre

Incorporation cost ~ $10/acre

Total cost ~ $70/acre

Assuming ~100 lbs of N fixed per acre, the cost is ~70 cents per lbs of N

Multi-functional cover crops

Cover Crops

Adapted from Magdoff and Weil (2004)

Cover crops generally require more management

Cover crops are not idiot –proof

There are few profits in idiot-proof systems!

Impact of cover crops on soybean cyst nematodes

Bare Cereal Rye Ryegrass

1 7533 717*117**

2 3650 320* 0**3 1559 722* 386*4 1202 390* 279*

2 years /3 replications

* Significant .05 ** Significant .01

_____________Egg count ______________

M Plumer

Site

Soil Density (g/cm3)all no-tilled 9+ years

Ryegrass cover crop

for 6 years

10” 1.49*

16” 1.58

24” 1.48*

No cover crop

1.66

1.54

1.65

* sig. .05

M Plumer

http://www.amazingcarbon.com/PDF/Rick%20Maurice%20-%20RTM%20Carbon%20Forum%20Sept%202005.pdf

Miscanthus

Aerial Seeding Turnips, Oats and Rye 8-20-2001

Cliff Schuette

Turnipsand Cereal Rye

Airseed 8/25/2000

Barkant Turnips-3 lbsRye 2 Bu

Airplane $8/AcreCorn 183 Bu/acre

Atrazine 1 lbPartner April 28

November 1, 2000Turnips - Spring Oats-

Corn StalksSeeded August 15

Turnips- 4 lbsOats 1 Bu.40 LBS N

November 1, 2000Spring Oats -Cereal Rye-

Corn StalksSeeded August 15

Oats- 1 Bu.Rye-1 1/2 Bu.

40 LBS N

11/30/00

Protein 16.59RFV 114

01/19/2001

Protein 12.79RFV 92

Paul Smith

Annual Rye grass

aerial seededinto standing

corn

Fall, 2001

John HebertInspecting Ryegrass No-till into

corn stubbleFall, 2001

Pluribus strip-till system in cereal rye

Dick Thompson