Correlating Soil Microbial Properties with
Crop Yields in the Canadian Prairies
Newton Z. Lupwayi1, K. Neil Harker2, Francis J. Larney1, Robert E. Blackshaw1 and John T. O’Donovan2
1Agriculture & Agri-Food Canada, Lethbridge Research Centre, Lethbridge, Alberta, Canada 2Agriculture & Agri-Food Canada, Lacombe Research Centre, Lacombe, Alberta, Canada
Introduction
• Soil microorganisms mediate many important biological processes for sustainable agriculture.
• However, correlations between soil microbial properties and crop productivity cannot always be demonstrated.
• Two case studies on the Canadian prairies were used to correlate soil microbial biomass with wheat and canola yields.
1. Spring Wheat in Irrigated Crop Rotations: 2002
to 2011 at One Site
3
Vauxhall, Alberta
4
Rotations Code Length Rotation Management
1CONV 1 Yr W Conventional
3CONV 3 Yr P-B-W Conventional
3CONS 3 Yr P-B-W Conservation
4CONV 4 Yr SB-B-P-W Conventional
4CONS 4 Yr SB-B-P-W Conservation
5CONS 5 Yr P-W-SB-W-B Conservation
W = wheat; P = potatoes; B = beans; SB = sugar beet
Outline of Conservation Practices used over 12 yr
1. Composted beef cattle manure as a substitute for inorganic fertilizer
2. Reduced tillage or direct seeding where possible
3. Beans: Narrow-row (20 cm) straight cut vs. wide-row (60 cm) undercut
Rotation
Cont Wht 3-CONV 3-CONS 4-CONV 4-CONS 5-CONS1 5-CONS2 6-CONS
Mic
rob
ial B
iom
as
s C
arb
on
, m
g/k
g s
oil
0
100
200
300
400
500
600
700
bc
c
ab
bc
ab
bc
a
bc
Microbial Biomass Carbon (MBC) in 2011
(but used 2002-2011 data for regression analysis)
8
Rhizosphere
0 200 400 600 800 1000 1200
0
2000
4000
6000
8000
10000
MBC (mg/kg soil)
Wh
ea
t g
rain
yie
ld (
kg
/ha
)
y = 3526 + 4.39x (adjusted r2 = 0.166**)
2. High-Yield No-Till Canola: Seven Sites
9
Seven Sites in the Canadian Prairies
10
Beaverlodge
Lacombe
Lethbridge Swift Current Indian Head
Brandon
Edmonton
Treatments
11
Treatment Seeding rate (seeds m-2) N rate (x recommended rate) N form
1 75 1 Uncoated
2 75 1 Uncoated + Fungicidea
3 75 1 Coated + Fungicide
4 75 1.5 Uncoated
5 75 1.5 Uncoated + Fungicide
6 75 1.5 Coated + Fungicide
7 150 1 Uncoated
8 150 1 Uncoated + Fungicide
9 150 1 Coated + Fungicide
10 150 1.5 Uncoated
11 150 1.5 Uncoated + Fungicide
Soil Characteristics at The Sites
12
Site Soil type pH OM (%) Clay (%)
Beaverlodge, AB Dark Gray Luvisola 6.5 5.4 22.0
Brandon, MB Black Chernozemb 8.1 5.0 33.0
Edmonton, AB Black Chernozem 7.6 13.0 36.5
Indian Head, SK Black Chernozem 7.6 3.2 21.4
Lacombe, AB Black Chernozem 6.4 8.3 21.0
Lethbridge, AB Dark Brown Chernozemc 8.0 3.0 33.0
Swift Current, SK Brown Chernozemd 6.5 3.4 18.2
Summary of Soil Microbial Results
• Treatment effects on soil MBC, β-glucosidase enzyme
activity or bacterial diversity were usually not significant.
• Where significance occurred:-
– Doubling the seeding rate from 75 to 150 seeds m-2 usually
increased these microbial properties.
– Increasing N rate to 1.5x the recommended rate had mostly
positive effects in canola rhizosphere.
– The effects of N form (including addition of fungicide) were
inconsistent.
13
14 MBC in rhizosphere (mg kg-1 soil)
0 500 1000 1500 2000
Gra
in y
ield
(kg
ha
-1)
0
1000
2000
3000
4000
5000
6000
7000
y = 1939 + 0.82x (r2
= 0.307**)
NS
2008: Microbial Biomass - All Sites 2 sites with
high org. C
Lacombe MBC
data - unusual
15
2008: Enzyme Activity - All Sites
Enzyme activity in rhizosphere
0 200 400 600 800 1000
Gra
in y
ield
(kg
ha
-1)
0
1000
2000
3000
4000
5000
6000
7000
y = 1413 + 2.55x (r2
= 0.457**)
y = 5630 - 0.698x (r2
= 0.041*) 2 sites with
high org. C
Lacombe enzyme
data - unusual
16 MBC in rhizosphere (mg kg-1 soil)
0 500 1000 1500 2000 2500
Gra
in y
ield
(kg
ha
-1)
0
1000
2000
3000
4000
5000
6000
2010 (3 sites): Microbial Biomass - Without Lacombe Data
y = 1361 + 1.84x (r2
= 0.744**)
No correlations within
sites.
Large, regional datasets
- important.
Swift
Current, SK
Beaverlodge, AB
Edmonton, AB
17
2010 (3 sites): Enzyme Activity - Without Lacombe Data
Enzyme activity in rhizosphere
0 200 400 600 800 1000
Gra
in y
ield
(kg
ha
-1)
0
1000
2000
3000
4000
5000
6000
y = 1217 + 5.44x (r2
= 0.610**)
No correlations within
sites.
Large, regional datasets
- important.
Root Maggot Damage
18 MBC in rhizosphere (mg kg-1 soil)
0 500 1000 1500 2000 2500
Ro
ot
ma
gg
ot
da
ma
ge
(1
to
5)
0.5
1.0
1.5
2.0
2.5
y = 1.55 - 0.00014x (r2
= 0.036*)
Biological pest control
Less root maggot damage
where MBC (and enzyme
activity) - high.
Conclusion
• Crop/soil management practices that increased soil
microbial biomass and enzyme activity were associated
with improved crop health and yields.
– Feedback: the crop affects rhizosphere soil microbials, which
in turn affect the crop.
• Multi-site experiments show the relationships better
than single-site, single-year experiments.
Acknowledgements