69th SWCS International Annual Conference “Making Waves in Conservation: Our Life on Land and Its Impact on Water” July 27-30, 2014 Lombard, IL

1. Cover crop
mixture
diversity,
biomass
production
and
weed
suppression
Angela Tran
University of Nebraska-Lincoln

2. Outline
The motivation
The question
The methodology
The outcome

3. THE MOTIVATION
Why study diverse cover crop mixtures?

4. Photo by Tom Stromme of The Bismarck Tribune.
Increasing interest in the use of
diverse cover crop mixtures.

5. Cover crop research
mainly on monocultures.
Photo from Practical Farmers of Iowa.

6. Cover crop mixture research
mainly on bi-cultures.
Photo from The Ohio State University Extension.

7. Little research on diverse, multi-
species cover crop mixtures.

8. 0
1000
2000
3000
4000
0 3 6 9 12
No.possiblecombinations
No. species
Possible combinations of n
species.

9. Missing fundamental information
about cover crop mixtures.
How are mixtures different from
monocultures?
Why?
How do I design my cover crop mixture?

10. THE QUESTION
What is it that we want to know?

11. What is the effect of
diversity
on
performance?
Diversity
Performance

12. Diversity
Performance
?

13. Diversity
Performance
?

14. Diversity
Performance
?

15. Defining performance
• Biomass production
• Weed suppression
Diversity
Performance

16. Defining diversity
• No. species
• No. functional groups
Diversity
Performance

17. Species

18. Functional groups

19. THE METHODOLOGY
How did we approach answering our research question?

20. No. Species Species
Functional
Groups
1 No Cover 0 0
2 Barley (Spring) 1 1
3 Oats (Spring) 1 1
4 Wheat (Spring) 1 1
5 Austrian Winter Pea 1 1
6 Mammoth Red Clover 1 1
7 Yellow Blossom Sweetclover 1 1
8 Radish 1 1
9 Rapeseed 1 1
10 Turnip 1 1
No. Species Species
Functional
Groups
1 No Cover 0 0
2 Barley (Spring) 1 1
3 Oats (Spring) 1 1
4 Wheat (Spring) 1 1
5 Austrian Winter Pea 1 1
6 Mammoth Red Clover 1 1
7 Yellow Blossom Sweetclover 1 1
8 Radish 1 1
9 Rapeseed 1 1
10 Turnip 1 1
Cover crop treatments (#1-10)
No. Species Species
Functional
Groups
1 No Cover 0 0
2 Barley 1 1
3 Oats 1 1
4 Wheat* 1 1
5 Austrian Winter Pea 1 1
6 Mammoth Red Clover 1 1
7 Yellow Blossom Sweetclover 1 1
8 Radish 1 1
9 Rapeseed 1 1
10 Turnip 1 1
No. Species Species
Functional
Groups
1 No Cover 0 0
2 Barley 1 1
3 Oats 1 1
4 Wheat* 1 1
5 Austrian Winter Pea 1 1
6 Mammoth Red Clover 1 1
7 Yellow Blossom Sweetclover 1 1
8 Radish 1 1
9 Rapeseed 1 1
10 Turnip 1 1
No. Species Species
Functional
Groups
1 No Cover 0 0
2 Barley 1 1
3 Oats 1 1
4 Wheat* 1 1
5 Austrian Winter Pea 1 1
6 Mammoth Red Clover 1 1
7 Yellow Blossom Sweetclover 1 1
8 Radish 1 1
9 Rapeseed 1 1
10 Turnip 1 1
*spring variety

21. No. Species Species
Functional
Groups
11 Grass Mix (Barley, Oats, Wheat) 3 1
12 Legume Mix (Peas, Red Clover, Sweetclover) 3 1
13 Brassica Mix (Radish, Rapeseed, Turnip) 3 1
14 Grass Mix + Legume Mix 6 2
15 Grass Mix + Brassica Mix 6 2
16 Legume Mix + Brassica Mix 6 2
17 Grass Mix + Legume Mix + Brassica Mix 9 3
18 Barley, Peas, Radish 3 3
19 Oats, Red Clover, Rapeseed 3 3
20 Wheat, Sweetclover, Turnip 3 3
Cover crop treatments (#11-20)
No. Species Species
Functional
Groups
11 Grass Mix (Barley, Oats, Wheat) 3 1
12 Legume Mix (Peas, Red Clover, Sweetclover) 3 1
13 Brassica Mix (Radish, Rapeseed, Turnip) 3 1
14 Grass Mix + Legume Mix 6 2
15 Grass Mix + Brassica Mix 6 2
16 Legume Mix + Brassica Mix 6 2
17 Grass Mix + Legume Mix + Brassica Mix 9 3
18 Barley, Peas, Radish 3 3
19 Oats, Red Clover, Rapeseed 3 3
20 Wheat, Sweetclover, Turnip 3 3
No. Species Species
Functional
Groups
11 Grass Mix (Barley, Oats, Wheat) 3 1
12 Legume Mix (Peas, Red Clover, Sweetclover) 3 1
13 Brassica Mix (Radish, Rapeseed, Turnip) 3 1
14 Grass Mix + Legume Mix 6 2
15 Grass Mix + Brassica Mix 6 2
16 Legume Mix + Brassica Mix 6 2
17 Grass Mix + Legume Mix + Brassica Mix 9 3
18 Barley, Peas, Radish 3 3
19 Oats, Red Clover, Rapeseed 3 3
20 Wheat, Sweetclover, Turnip 3 3
No. Species Species
Functional
Groups
11 Grass Mix (Barley, Oats, Wheat) 3 1
12 Legume Mix (Peas, Red Clover, Sweetclover) 3 1
13 Brassica Mix (Radish, Rapeseed, Turnip) 3 1
14 Grass Mix + Legume Mix 6 2
15 Grass Mix + Brassica Mix 6 2
16 Legume Mix + Brassica Mix 6 2
17 Grass Mix + Legume Mix + Brassica Mix 9 3
18 Barley, Peas, Radish 3 3
19 Oats, Red Clover, Rapeseed 3 3
20 Wheat, Sweetclover, Turnip 3 3
No. Species Species
Functional
Groups
11 Grass Mix (Barley, Oats, Wheat) 3 1
12 Legume Mix (Peas, Red Clover, Sweetclover) 3 1
13 Brassica Mix (Radish, Rapeseed, Turnip) 3 1
14 Grass Mix + Legume Mix 6 2
15 Grass Mix + Brassica Mix 6 2
16 Legume Mix + Brassica Mix 6 2
17 Grass Mix + Legume Mix + Brassica Mix 9 3
18 Barley, Peas, Radish 3 3
19 Oats, Red Clover, Rapeseed 3 3
20 Wheat, Sweetclover, Turnip 3 3

22. Cover crops broadcasted…
After small grains
harvest (3)
Into maturing
soybeans (3)
Into maturing corn (2)
or after seed corn
harvest (1)

23. Across nine fields at six farms.

24. Sampling and measurements
Species specific cover crop and weed
biomass sampled before fall frosts .
Plant tissue dried to a constant weight
at 65°F.
Cover crop and weed biomass
sampled before fall frosts.

25. THE OUTCOME
What have we found so far?

26. Cover crop establishment
highly variable across sites.

27. Only one site with substantial
cover crop growth.
Hooper, NE (harvested wheat field)
Cover crops seeded 8/31/13.
Plant biomass sampled 10/31/13.

28. Biomass production
Data has many possible narratives.
An ecological narrative
• Pre-existing framework
• ↑ diversity, ↑ productivity
An agronomic narrative
• More relevant to agricultural management?
• < diverse systems can be just as productive as
> diverse systems

29. 0
1000
2000
3000
4000
0
100
200
300
400
500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Barley Oats Wheat
Pea Red Clover Sweetclover
Radish Rapeseed Turnip
Error bars (±SEM).
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)
Treatment No.

30. An ecological narrative
Tilman, D. 2001. Functional Diversity. p. 109-120 in S. A. Levin (ed.) Encyclopedia of biodiversity. Academic
Press: San Diego, CA.
Tilman, D., J. Knops, D. Wedin, P. Reich, M. Ritchie, E. Siemann. 1997. The Influence of Functional Diversity and
Composition on Ecosystem Processes. Science 277: 1300-1302.

31. 0
1000
2000
3000
0 1 2 3 4 5
0
100
200
300
400
0 3 6 9
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)
No. functional groupsNo. species
Data fit to rectangular hyperbola (Y = I*X/[1+(I/A)*X]). Error bars (±SEM).

32. An agronomic narrative
Less concerned with averages.
More concerned with instances.
Are there instances where less
diverse systems produce more than
more diverse systems?

33. 0
1000
2000
3000
0 1 2 3 4 5
0
100
200
300
400
0 3 6 9
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)
No. functional groupsNo. species
Species diversity confounded with
functional diversity.

34. 0
1000
2000
3000
0
100
200
300
400
Grasses Legumes Brassicas
1 species 3 species
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)
Functional group
Error bars (±SEM); p-value <0.10.
NS
NS
NS

35. Monocultures and 3-way mixes
within the same functional
group performed the same.
On average.
Not in every instance.

36. Error bars (±SEM); p-value <0.01.
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)
-----------NS-----------
Functional group
Grasses Legumes Brassicas
A
B
B
B
A
B
B B
0
1000
2000
3000
4000
0
100
200
300
400
500
Barley Oats Wheat
Pea Red Clover Sweetclover
Radish Rapeseed Turnip

37. With regard to species diversity
alone, monocultures can
outperform mixtures.

38. What about with regard to
functional diversity?

39. B
A
0
1000
2000
3000
0
100
200
300
400
1 3
No. species = 3; p-value <0.01.
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)
No. functional groups

40. Increasing functional diversity
increased biomass production.
On average.
Not in every instance.

41. 1 3
No. functional groups
-------------------NS-------------------
No. species = 3; p-value <0.01.
B
C
A
0
1000
2000
3000
4000
0
100
200
300
400
500
Barley Oats Wheat
Pea Red Clover Sweetclover
Radish Rapeseed Turnip
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)

42. Biomass production
Possible narratives
Ecological—↑ diversity, ↑ productivity
The narrative of averages
Agronomic— < diverse systems can be
just as productive as > diverse systems
The narrative of instances

43. Weed Suppression
Data range limitations prevented
evaluation of the relationship between
mixture diversity and weed suppression

44. 0
10
20
30
40
0 100 200 300 400
Weedbiomass(g/m2)
Cover crop biomass (g/m2)
No cover
Legume only covers
All other covers

45. Looking Forward
Beyond biomass
Nutrient cycling
Faunal biodiversity
Adding functional groups
Warm season grasses, legumes,
broadleaves

46. QUESTIONS/COMMENTS
Cover crop mixture diversity, biomass production and
weed suppression

47. EXTRA SLIDES
Cover crop mixture diversity, biomass production and
weed suppression

48. Biomass production
On the mechanisms behind diversity-
productivity relationship
Suggested mechanisms include the idea that
one species enhances the success of another.
For this project, however, mechanism may be
a simple artifact of the relationship between
seeding rate and biomass.

49. 0
1/3
2/3
1
Full2/31/3
Biomasspotential
Seeding rate

50. Radish as an example
Recommended broadcast rate*: 8-14 lb/A
Selected rate for this project: 15 lb/A
With ≈ 25,000 seeds/lb, that is seeding ≈ 9 seeds/ft2.
*Clark, A. (ed.) 2007. Managing cover crops profitably. 3rd ed. SARE Program, College Park, MD.

51. 0
1000
2000
3000
4000
0
100
200
300
400
500
8 18
Barley Pea Radish
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)
Treatment No.
Could more diverse systems be more economical ways to get more biomass?

52. Seeding dates
Location Field Type Seeding Date
Keene, NE Wheat stubble 7/19/13
Marquette, NE Barley stubble 8/10/13
Hooper, NE Wheat stubble (disked) 8/31/13
Mead, NE Soybean (R5) 9/10/13
Hooper, NE Soybean (R7) 9/12/13
Marquette, NE Soybean (R6) 9/14/13
Hooper, NE Corn 9/12/13
Waterloo, NE Corn stubble (disked) 9/19/13
Bladen, NE Corn 9/20/13

53. Seeding rates
Species
Full broadcast rate (lb/A)
Suggested * Selected
Barley 80-125 150
Oats 110-140 150
Wheat 60-150 150
Austrian winter pea 90-100 100
Red clover 10-12 15
Yellow blossom sweetclover 10-20 15
Radish 10-20 15
Rapeseed 8-14 15
Turnip 10-12** 15
*Clark, A. (ed.) 2007. Managing cover crops profitably. 3rd ed. SARE Program, College Park, MD.
**Björkman, T. 2009. Forage Turnips and Rape. Available at
http://www.hort.cornell.edu/bjorkman/lab/covercrops/turnip.php (verified 3 Mar . 2013). Cornell University, Cornell, NY.

54. Liz Morrison, Corn and Soybean Digest (Jan. 1, 2011).
John Dietz, Hay & Forage Grower (Aug. 1, 2008).
Graze (May 1, 2013).
Cover Crop Cocktail Research Team, Penn State College of Agricultural Sciences (2013).
This image cannot currently be displayed.
Andrew McGuire, Washington State University (April 17, 2013).
This image cannot currently be displayed.
This image cannot currently be displayed.
John Michaelson, Tennessee News Service (Jan. 20, 2014).

55. C
B
B
AB
A
0
1000
2000
3000
0
100
200
300
400
0 1 3 6 9
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)
No. species
Error bars (±SEM); p-value <0.10.

56. C
B
AB
A
0
1000
2000
3000
0
100
200
300
400
0 1 2 3
Error bars (±SEM); p-value <0.01.
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)
No. functional groups

57. D
C
B
A
0
1000
2000
3000
0
100
200
300
400
0 1 2 3
Error bars (±SEM); p-value <0.01
All three species included for addition of each functional group.
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)
No. functional groups

58. 0
1000
2000
3000
4000
0
100
200
300
400
500
2 5 8 18
Barley Pea Radish
Treatment No.
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)

59. 0
1000
2000
3000
4000
0
100
200
300
400
500
2 5 8 AVG(2,5,8) 18
Barley Pea Radish
Treatment No.
Covercropbiomass(g/m2)
Covercropbiomass(lb/A)

60. 0
8
16
24
0
20
40
60
0 20 40 60 80 100 120
Depth(in)
Depth(cm)
Soil Nitrate (ppm)
No Cover
9-Way Cocktail
p-value < 0.10 (*), <0.01 (**)
*
*
**
**

61. 0
8
16
24
0
20
40
60
0 20 40 60 80 100 120
Depth(in)
Depth(cm)
Soil Nitrate (ppm)
No Cover
Grass Mix
Legume Mix
Brassica Mix
9-Way Cocktail
p-value < 0.10 (*), <0.01 (**)
*
**
**
**

62. 0
8
16
24
0
20
40
60
0 4 8 12 16 20
Depth(in)
Depth(cm)
Soil Sulfate (ppm)
No Cover
Grass Mix
Legume Mix
Brassica Mix
9-Way Cocktail
p-value < 0.10 (*), <0.01 (**)
*
**
*
*

63. 0
8
16
24
0
20
40
60
0 4 8 12 16 20
Depth(in)
Depth(cm)
Soil Ammonium (ppm)
No Cover
Grass Mix
Legume Mix
Brassica Mix
9-Way Cocktail
NS
p-value < 0.10 (*)
*
NS
*

64. 0
8
16
24
0
20
40
60
0 40 80 120 160 200 240
Depth(in)
Depth(cm)
Soil Phosphorus (ppm)
No Cover
Grass Mix
Legume Mix
Brassica Mix
9-Way Cocktail
p-value < 0.10 (*), <0.01 (**)
**
NS
NS
NS

65. 0
8
16
24
0
20
40
60
0 200 400 600 800 1000
Depth(in)
Depth(cm)
Soil Potassium (ppm)
No Cover
Grass Mix
Legume Mix
Brassica Mix
9-Way Cocktail
p-value < 0.10 (*), <0.01 (**)
*
NS
*
*

66. This image cannot currently be displayed.
It makes little sense if you know what you are doing.
Diversification is protection against ignorance.
Photo by Ben Baker of Redux.