2017 SWCS Annual Conference July 30-August 2, 2017 Monona Terrace Convention Center

1. Sarah Carlson
Practical Farmers of Iowa
Midwest Cover Crop Director
sarah@practicalfarmers.org 515-232-5661
Cover Crops, not just for Conservation Anymore
Cover Crop Effect on Weeds in the Northern Cornbelt:
a meta-analysis

2. Weed Pressure Early
No Cover Crop
Photos from Jason Ness, Coon Rapids

3. WHAT ARE FARMERS’
COVER CROP GOALS?
• Livestock feed?
• Nitrogen scavenging?
• Manure management?
• Improved water quality?
• Weed control?
• Reduced soil erosion?
• Increased yield?
• Build soil carbon?
• Make a landlord happy?
• Wildlife benefit?

4. Take home messages
WHY is the Cornbelt “leaky”?
HOW does Practical Farmers work?
WHAT are our Meta-analysis results?

5. WHY IS
THE CORNBELT
“LEAKY”?

6. Soybean
Small Grain +
Legume
Corn

8. 52% of precipitation occurs between Oct-May in central Iowa
Heggenstaller et al. (2008)
Greatest loss of nutrients is outside the cropping season (Kaspar et al., 2007)

10. HOW DOES PRACTICAL
FARMERS WORK?

11. When should I kill
cover crops before
soybeans?

13. $50+
$10+

14. Great weed
control!

15. META-ANALYSIS TEAM
CHRIS WILBECK
ALISHA BOWER
STEFAN GAILANS

16. Criteria
i) Research conducted in IL, IN, IA, MI, MN, OH, WI
(Upper MS Basin)
ii) corn or soybean harvested for grain was the main
crop;
iii) cover crops were seeded August prior to main crop;
iv) weed biomass or density or % control, cover crop
species and biomass, and main crop yield was available.
Research years of studies: 1985-2013

19. Yield Response variable
calculated
Yield (with cover crop) ÷
Yield (without cover crop)
Moderating Variables Evaluated:
•Cover Crop Aboveground Biomass
•Cover Crop Type
•Cover Crop Planting Date & Termination
Date/Method
•% Weed Control
Weed Response variable
calculated
Weed Bio (with cover crop) ÷
Weed Bio (without cover crop)

20. Cover Crop (CC) Effect on Weeds in C-S
• CC biomass
negatively correlated
with weed biomass
• Increase CC biomass
(2500+ lbs/A) to reach
50% total weed control
potential
• Greater grass cc biomass
could decrease corn yield
• Researchers sampled
larger cc in soybean
studies
• Slight soybean yield bump
with greater cc biomass

24. Brassica
Grass
Legume
Yield (cc) /
Yield (no cc)
Corn
Cover Crop Biomass (lbs/A)

25. Yield (cc) /
Yield (no cc)
Soybean
Cover Crop Biomass (lbs/A)
Grass

26. Cover Crop (CC) Effect on Weeds in C-S
• CC biomass
negatively correlated
with weed biomass
• Increase CC biomass
(2500+ lbs/A) to reach
50% total weed control
potential
• Greater grass cc biomass
could decrease corn yield
• Researchers sampled
larger cc in soybean
studies
• Slight soybean yield bump
with greater cc biomass

27. USE THE CASH IN COVER CROPS TO SCALE CONSERVATION

28. Take home messages
pficovercrops@practicalfarmers.org
Sarah Carlson
sarah@practicalfarmers.org
515-232-5661
WHY is the Cornbelt “leaky”?
HOW does Practical Farmers work?
WHAT are our Meta-analysis results?