This presentation was the Keynote address for the Innovative Farmers of Ontario (Canada) in February 2014. Some slides may not work as well as intended without their animations.

1. More Than Just Cover
Cover Crops as Multipurpose
Tools for Soil Quality
Ray Weil
Professor of Soil Science

2. “Cover crop”, “Green manure”,
“Catch crop”
In factcall them, thesecrops,grown for
using cover crops
• Whatever you
changes everything!
the soil can do a lot more than just prevent
erosion.
Resource efficiency
Biological diversity
Soil quality

3. Harvest
Planting
Cover crops can utilize
otherwise wasted resources
The sun shines, the rain falls and microbes work 12 months a year, but
this typical mid-west grain farm captures only 3-4 months of this activity.

4. Cover Crops Liberate Farmers from
Market Dictates on What to Plant
1. Cool season
grasses
2. Cool season
Legumes
3. Cool season
Brassicas
4. Warm season
grasses
5. Warm season
legumes
6. Warm season
broadleaves

5. Cover crops change everything!
Cover
crops
Labile C
Soil
organic
matter
Increased
infiltration
Soil Cover
Soil
temperature
Rhizobial
associations
Mycorrhizal
associations
Nutrient capture
(N, P, S, K, etc)
Reduced
erosion loss
Soil
Aggregation
Reduced
evaporation
Weed
suppression
Food
web
activity
Bio-drilling
Enhanced
crop
growth
Soil
water
Nematodes
P- fertility
Reduced leaching
loss (N)
Nitrogen
fertility

6.  Plan your cover crop as
carefully as your cash crops.
 What do you want a cover
crop to do?
 What is your niche and
growing window?
Alternate drill rows of rye and radish
After trying single
cover crops, you
may want to try
simple mixtures.
Pure radish
Alternate drill rows
of Sudex and radish

7. Farmers are good at figuring out ways to extend
their cover crop planting window!

8. Even a simple rye cover crop can make a
measurable difference to your soil
Cover Crop Treatment
Crop or Soil Parameter
No Rye
Rye
Soybean plant, kg ha-1
5275.5
**
5995.1
Soybean yield, kg ha-1
2704.8
*
3054.9
Active C mg kg-1
624.2
**
661.7
C respired in 2 days, mg kg-1
213.1
**
255.0
Total organic C g kg-1
17.90
ns
19.06
Mineralizable N mg kg-1
82.01
**
101.81
Stable aggregates %
60.40
**
69.40
Overall Means of 6 sites in MD and PA with 2 to 6 years of
rye cover crop in corn – soybean rotation.

9. A single rape or rye cover crop changed the soil
food web from bacterial to fungal-dominated.
Data taken 8 months after
cover crops were
Fungal-feeding killed.
Coslenchus sp.
nematode
Gruver, Weil, Zasada, Sardanelli, and Momen 2010 (J. of Applied Ecology).

10. Earthworms
and cover crops
work together.

11. Key differences are in the roots!

12. Harvested part (grain, fruit, leaves)
Shoot residues
Animal feed
Fuel
Roots
Rhizo-deposition
CO2
Soil
organic
carbon
SOC
100 kg C as leaves  ~ 15 kg SOC 1 year after incorporation.
100 kg C as roots  ~ 30 kg SOC 1 year after incorporation.

13. Soil C content
0
Soil Depth, m
> 90% of the data is here.
1
Leaching
and
re-adsorption
of dissolved
organic carbon
DOC
2
Roots
and
rhizodeposition
Much more
effort is
needed to
study deep
soil C
> 60% of the
carbon is here.
SOC in deep layers
tends to have low
C/N and slow
turnover times.

14. Researchers are no longer so sure that no-till
increases total profile organic carbon.
Depth distribution of corn roots
Amount of of C measurements
Distribution soil carbon soil
No-till
Plowed
But very few of the
tillage comparison
included cover crops!
Root system of a corn plant (field excavation by Weaver 1929) and the sampling depths
used in 140 comparative studies of tillage impacts on soil carbon. Scale in feet.
Baker, J.M., T.E. Ochsner, R.T. Venterea, and T.J. Griffis. 2007. Tillage and soil carbon
sequestration--what do we really know? Agriculture, Ecosystems & Environment 118:1-5.

15. Cover crop roots build soil bio-physical
quality

16. A little extra organic matter goes a long way to
stabilize aggregates and keep soil surface open.
1.2% OM
2.0% OM

17. Cover crops can
improve structure
deeper in the soil
More on biodrilling
to fight compaction
in the break out
session tomorrow!

18. Cover crop surface residues
influence:
• Soil temperature
• Soil moisture
• Weed pressure
Forage radish
residues
Spring oat
residues

19. Four stages of a
unique cover crop
19

20. Vegetation and residues dramatically
suppress weeds and influence no-till
seedbed conditions.
Rye
Forage Radish

21. Forage radish “film” during rapid
decomposition

22. Effect of living rye v decayed forage
radish on soil temperature at 5 cm
depth in April in Md.
(oC)
25
20
15
10
5

23. Effect of living rye v decayed
forage radish on soil water at
5 cm depth in April in Md.

24. Soil moisture at 5 cm after cover crop
treatments, Clarksville Md 2013
Workable days (below 80% plastic limit)

25. Zoned
cover crop mixtures

26. Like deep ripping
and using a burn
down herbicide in the
planting row
while mulching the
inter-row
Radish planted on 75cm
(30”) centers with 3 rows
of oats drilled in between.
September
Joel Gruver,
Western Illinois Univ.
26
photo by Joel Gruver, UWI

27. Another major cover crop function:
enhanced nutrient management
Reduce losses
Enhance availability
Add nitrogen
Recover deep nutrients

28. Why use cover crops to
manage nutrient loss?
The environment
• Nutrient leaching (N)
• Runoff/erosion (P)
Farm
profitability
Source
Price / kg
N
Price /
kg P
Urea
Lake Erie
$1.40
DAP
$1.40
Legumes
Dairy
manure
$2.75
Cost of
seed, land,
labor, lost
crop
?
?

29. Very complex
as N occurs in
•Solids
•Liquids
•Gases
Blue = anaerobic processes
Bright green = N addition to soil
Dark olive = N losses to water
The N Cycle
From Weil and Brady 2015 The Nature and Properties of Soils.

30. Inputs
of N to
soil
organic
matter
as plant
and
animal
residues
.

31. Decomposition
of residues
and release of
N by
mineralization.
SOM
R-NH2
Decomposition
promoted by:
• Good aeration
• Warm
temperature
• Easy to digest
carbon
• Tillage
NH4+

32. Grass turns greener
because Fairy ring fungi
release N from SOM

33. Oxidation N from soil
Conversion ofof Ammonium
to Nitrate
organic matter to soluble
mineral forms.
Organic matter
Soil organisms
NO3-
Nitrate
NH4+
NO2nitrite
Leaching
loss
Ammonium
Nitrification needs:
•Oxygen (aeration)
•Warm temperature
•Presence of nitrifiers

34. In a soil with 2.5% organic matter, the
top 30cm has:
~4000 kg/ha ORGANIC Nitrogen
< 100 kg/ha Inorganic N/year
• nitrate-N
• ammonium-N
• other forms (gases etc.)

35. Crop use of N and P
Crop
Yield
N
P
Canola
3000 kg seed
119
19
Corn
9000 kg grain
133
25
Soybean
3100 kg grain
199
20
Wheat
3700 kg grain
69
13
To estimate N_P_K in harvest, use tool at
https://plants.usda.gov/npk/main

36. Nutrient capture:
nitrogen in fall

37. Soil v Cover Crop or Weed
Nitrogen Contents in November
12080 =
40
 150 kg N taken up by the
cover crop
 40 kg N missing from the
upper 1 m of soil
 Where did the other 110 kg
N come from?
 From deeper soil layers?
150 kg N taken up by plants
Data: Wang and Weil,
unpublished

38. Nitrate-N in 180 cm soil
No cover:
173 kg/ha
Forage radish: 48 kg/ha
Oilseed radish: 62 kg/ha
Last spring’s fertilizer
2 years ago
fertilizer
Loamy sand,
Beltsville, Maryland
After corn-wheat
Dean, J.E., and R.R. Weil. 2009. Journal
of Environmental Quality 38:520-528.

39. A few weeks later planting reduces weed
suppression and biodrilling
but not nitrogen capture.
Effect of seeding date on forage radish growth & nitrogen uptake in fall
Effect of seeding date on forage radish dry matter and N uptake. Means of 3 locations in 2007.
4.625
Shoot dry matter
5250
4625
4000
3375
2750
Shoot tissue N, %
Shoot DM, kg/ha
5875
250
5.000
Tissue N conc.
4.250
3.875
3.500
3.125
2.750
225
Shoot N Uptake, kg/ha
6500
Shoot N uptake
200
175
150
125
100
2125
2.375
75
1500
2.000
50
1
2
3
4
5
Seeding date, weeks after Aug. 20
1
2
3
4
5
Seeding date, weeks after Aug. 20
1
2
3
4
5
Seeding date, weeks after Aug. 20
Means of 3 sites

40. Nitrogen Capture by October-Planted need to get
Timing is everything! – We Rye Cover Crop
Topsoil N tied
cover crops planted earlier!up by rye
2
10
15
50
Large amounts of N lost
September
October
November
March
April

41. Nitrogen Capture by Early of early planting and
Some advantagesSept-Planted Radish Cover Crop
frost killing. N available to early
25
September
125
200
October
November
?
N
?
planted cash crop
March
April

42. Nutrient capture:
nitrogen in spring
Soil
May 10th

43. Soil Nitrate (0-20 cm)
Nitrate-N
33 (kg ha-1)
increase from
radish
Nitrate-N
34 (kg ha-1)
increase from
radish
N mineralization in spring
Lounsbury and Weil 2013

44. Maize Response to Early Spring Nitrogen
Release by Radish Cover Crop
Following radish
Following rye

45. Increased available phosphorus in surface soil horizons
Silt loam, upper 120 cm
In 3rd winter of cover crop trts.
0
lsd 0.05
25
lsd 0.05
Cover crops
can enhance
topsoil fertility
with more than
just nitrogen
Soil depth
lsd 0.05
50
ns
ns
75
ns
ns
100
ns
125
0
No cover
Forage radish
Oilseed Radish
Rapeseed
Cereal rye
20
40
60
80 100 120
Soil test P (Mehlich 3), mg/kg
•Deep P brought to surface & bound P made available
140

46. P Concentration around radish holes
White and Weil (2009)

47. Sulfate in Topsoil (0-20 cm)
Clarksville
Wye
Lounsbury and Weil 2013

48. Brassicas are exceptionally high in certain nutrients:
calcium, phosphorus, sulfur , boron
Calcium contents
Phosphorus contents

49. Deep Soil
Nutrients:
Neglected Resource
under your feet?

50. Some Nutrient Capture
Questions Needing Research
1. How big is the deep N pool in early fall ?
2. How does aerial seeding in Aug compare to
drilling in Oct?
3. Can irrigation or seed coating ensure early
stands with aerial seeding?
4. Can on‐the‐spot nitrate‐N tests predict need
for covercrop starter N?
5. Can ~15 lbs starter N allow covercrops to
capture 100 lbs of extra N?
6. Can cash crops use the captured N (+P, K, S) in
spring?

51. Think about…
Managing plants to
soils
improve plants
soils
Questions?