Soybean Yield, Management and
Physiology: Comparison To Corn
North Central Branch, ASA
March 16-17, 2005
Emerson D. Nafziger
Crop Sciences
University of Illinois
Outline for Today
• Current status of soybean yields
• Yield physiology
• Weather interactions
• Management issues
• Summary and “proposal”
Yield, bu/acre
Illinois Corn Yield
200
180
160
140
120
100
80
60
40
20
0
1920
1940
1960
Year
1980
2000
Illinois Soybean Yields
Yield, bu/acre
60
50
40
30
20
10
0
1920
1940
1960
Year
1980
2000
Ratio, bu/ac:bu/ac
IL Corn:Soy Yield Ratio, 1920-2004
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1920
1940
1960
Year
1980
2000
Yield Variability (CV) by IL CRD, 1990-04
25
Corn
Soybean
Yield CV, %
20
15
10
5
0
NW
NE
W
C
E
WSW ESE
Crop Reporting District
SW
SE
IL
Corn & Soy Acreage, NW MN
Corn
1200
Soybean
1000
800
600
400
200
04
20
03
20
02
20
01
20
00
20
99
19
98
19
97
19
96
19
95
0
19
Acres, thousands
1400
Yields, NW MN
140
120
Corn
Soybean
Bu/acre
100
80
60
40
20
0
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
C:S Yield Ratio, All MN
7.00
All MN
6.00
NW MN CRD
5.00
4.00
3.00
2.00
1.00
0.00
95
96
97
98
99
00
01
02
03
04
Corn and Soybean Acreage in Illinois, 1990-2004
12
Acres, millions
11
10
9
8
Soybean
Corn
7
6
1989
1991
1993
1995
1997
Year
1999
2001
2003
2005
For Soybean Yield, How High is “High”?
• R. Cooper (in IL and OH) reported over 100 bu in subirrigated semi-dwarf types
• 300K seeds/acre in 7-in rows
• The reported world record (Ray Rawson) is 118 in MI
• 100+ bu/acre in county strip test in NW Illinois in 1990 on
a “virgin” field
• Highest county average yield was 57 bu/acre in 1998 in
JoDaviess County and in 2002 and 2004 in Carroll County,
both in NW Illinois
• Highest yield in the UI variety trials was 82 bu/acre at
Perry in 2004
• Highest Illinois state avg yield is 50.5 (2004)
Why Not Higher Soybean Yields?
• A partial list, compared to corn:
• Soybean has ~50 percent higher energy
content per lb of seed and 7% heavier
bushels than corn
• It does photorespiration, losing up to 1/3rd
of photosynthesis to this “useless” process
• It fixes some of its own N
• It fills rapidly for ~30 days v 45-50 for corn
• More sensitive to air pollutants(?)
A3244(97)-54 bu
W82(97)-42 bu
7
A3244(98)-61 bu
6
W82(98)-42 bu
LAI
5
4
3
2
1
0
3-Jun
23-Jun
13-Jul
2-Aug
22-Aug
Date
11-Sep
1-Oct
21-Oct
Urbana and Monmouth, 1999
14000
12000
W82-plant
A 3244-plant
lb per acre
10000
W82-seed
A 3244-seed
8000
6000
4000
2000
0
3-Jun
3-Jul
2-Aug
1-Sep
1-Oct
Yield v maturity date, Reg. 3, MG 3 RR, 2004
80
75
Yield, bu/ac
70
65
60
55
50
45
40
9/5
9/10
9/15
Date of maturity
9/20
9/25
Yield v maturity date, Reg. 3, RR, 2000
65
60
Yield
55
50
45
40
9/1
9/6
9/11
9/16
Maturity date
9/21
9/26
10/1
Soybean Yield Physiology
• The ability to maintain high photosynthetic rates
throughout seed filling stages defines high yield potential
• Among C3 crops, soybean has relatively high
photosynthetic capacity
• The maximum sustained seed fill rate is ~3 bushels per
day
• This fill rate sustains for ~30 days under normal temps;
can be longer if cooler
• By far the largest reason for decreased Ps causing lower
seed fill and yield is inadequate water
A Mystery of Soybean Yield Physiology
• There is no clear indication whether
soybean is “source-limited” (inadequate
Ps) or “sink-limited” (not enough places to
accept Ps products = sugars)
• This “confusion” may be of minimal
importance as long as breeders can
maintain progress, but it’s still of interest
in the field
Evidence for Source Limitation
• Increasing CO2 in the atmosphere increases
yields (SoyFACE & others)
• Ozone & other pollutants reduce yield
• Defoliation reduces yield, if it’s severe enough
• Drought reduces yield, often by reducing seed
size
Evidence for Sink Limitation
• Removing some leaves increases Ps rate in
remaining leaves
• Pale green (low chlorophyll) mutants yield more
than Ps rates would suggest
• Leaves accumulate starch during the day;
inability to utilize sugar fast enough?
• Adding N fertilizer (low fixation) fails to increase
yields
“Practical” Yield Physiology
• With exceptions, soybean plants initiate enough seeds for
high yields, but may fail to adequately sustain pods or fill
seeds due to reduced Ps during critical stages (R5-R6)
• Canopies and leaves are usually adequate, but root
systems often fail to provide enough water to maintain Ps
• With potential seedfilling rates of 3 bu/day, reductions in
Ps for even short stretches in August hurt yields
• Starting to fill seeds slightly earlier or extending
seedfilling slightly longer can increase yields greatly
Soybean Reproductive Development
R1 R2 R3
R4
R5
R7
R6
R8
Seed Filling
Pod Development
Flowering
Indeterminate Growth
Vegetative Growth
0
10
20
30
40
50
60
70
Days after flowering
©Palle Pedersen
Seed and Pod Development
R5
R6
R7 (1)
R8 (all)
©Palle Pedersen
ay
M
1ay 10
1
M 1-2
ay
0
2
Ju 1-3
ne 1
Ju 1-1
ne
0
1
Ju 1-2
ne
0
21
Ju -30
ly
Ju 1-1
0
ly
11
Ju -2
0
ly
21
Au -31
g
Au 1-1
0
g
1
Au 1-2
0
g
21
Se -31
p
Se 1-1
0
p
11
-2
0
M
Average high temperature, F
Freeport, Illinois
100
90
80
70
60
50
40
2003
2004
30
20
10
0
M
ay
M 1-1
ay
0
11
M
ay - 20
21
Ju -3
ne 1
Ju 1ne 10
Ju 11ne 20
21
Ju -30
ly
Ju 1-1
0
ly
11
Ju -2
ly
0
21
Au -31
g
Au 1-1
0
g
1
Au 1-2
0
g
21
Se -31
p
Se 1-1
0
p
11
-2
0
Average low temperature, F
Freeport, Illinois
70
60
50
40
30
2003
2004
20
10
0
M
ay
M 1-1
ay
0
1
M 1-2
ay
0
21
Ju -3
ne 1
Ju 1ne 10
Ju 11ne 20
21
Ju -30
ly
Ju 1-1
0
ly
1
Ju 1-2
0
ly
21
Au -31
g
Au 1-1
0
g
11
Au -2
0
g
21
Se -31
p
Se 1-1
0
p
11
-2
0
Rainfall, inches
Freeport, NW Illinois
6
2003
2004
5
4
3
2
1
0
Soybean management goals:
• To enable to crop to take full advantage
of good weather when it happens
• To protect the yield of the crop, at least
partly, from disastrously low yields
when the weather is poor
• In practical terms, we need to
“position” the crop for maximum
seedfilling rates
Planted Apr. 5
Photo May 24
Planting Date & Rate
ave. 9 No. IL sites, 2001-03, mid-maturity, 4 seeding rates
Ave. Yield, bpa
50
47.9
48
47.9
45.8
46
44
42.4
42
40
Early Apr
Late Apr
Early May
Planting Date
Late May
Effect of Planting Date on Maturity
and Plant Height
(response to day length)
Planting
Date
April 11
Maturity
Date
Sept. 16
Plant Heightin.
28.9
April 24
Sept. 17
30.5
May 11
Sept. 22
31.6
May 29
Sept. 28
33.2
Monmouth
Planting Date and Seeding Rate
E. Central Illinois, 4 yr
60
Yield, bu/acre
50
40
30
Mid-Apr
20
E. May
Mid-May
10
E. June
0
50
100
150
200
250
Seeding rate, 000/acre
Data from J. Gander, Pioneer Hi-Bred
Planting Date and Seeding Rate
60
Yield, bu/acre
50
40
6-Apr
30
24-Apr
9-May
20
26-May
10
0
50
100
150
200
250
Seeding rate, 000/acre
University of Illinois
Planting Rate and Variety
92B74
East Central Illinois
92B84
93B01
55
Yield, bu/acre
93B26
50
93B36
93B47
45
40
35
30
50
100
150
200
250
Seeding rate, 000/acre
Data from J. Gander, Pioneer Hi-Bred
Seeding Rate and Row Spacing
Avg of 14 Site-Years, N. IL
60
Yield, bu/acre
55
50
45
Drill
40
15-inch
30-inch
35
30
100
125
150
175
200
225
250
Seeding rate, 000/acre
E. Adee, University of Illinois
Seeding Rate and Row Spacing
Iowa, 3 site-years, 2004
80
Yield, bu/acre
70
60
50
15-inch
40
30-inch
30
20
10
0
50
100
150
200
250
Seeding rate, 000s/acre
P. Pedersen, Iowa State Univ.
Seeding Rate Economics
$15.00/125K unit; $5.00 per bu soybean
Yield, bu/acre
50
↑ Optimum
45
40
35
30
50
100
150
200
250
Seeding rate, 000/acre
University of Illinois
Variety Maturity & Planting Date, 2001-03
Avg. of 9 N. Ilinois Trials
60
Early
Mid
Yield, bu/acre
50
Late
40
30
20
10
0
Early Apr
Late Apr
Early May
Planting date
Late May
Inoculants on Soybean, 2004
Untreated
70
Optimize
Launcher
68
Prosurge
Yield, bu/acre
66
64
62
60
58
56
North
Central
South
Illinois locations (2 per region)
Average
Lactofen on Soybean, Urbana, 2004
70
Yield, bu/acre
65
60
55
50
45
40
Control
Cobra
Phoenix
Planting Management
• 100,000 plants per acre is enough to maximize yield,
if they’re all healthy and evenly distributed
• Variety, varietal maturity, row spacing, and planting
date don’t seem to affect seeding rate/plant
population response much
• Good quality soybean seed responds little if any to
seed fungicidal seed treatment or inoculant
• Planting in the first half of May is appropriate for
soybean, with little loss 1-2 weeks on either side of
that period
Soybean yield
Monmouth Rotation, 2002-04
70
Tilled
60
No-till
50
40
30
20
10
0
WCS
CWS
Rotation
SSS
CS
Monmouth CCS Soybean, 2004
72
70
93B67 HY
Yield, bu/acre
68
93B47 DEF
66
64
62
60
58
56
CCS
CS
Rotation
6 Illinois Soybean Sites, 2000-03
48
Spr NT
Yield, bu/acre
Spr Till
47
46
45
44
No-Till
Chisel
Deep Rip
According to Some…
High corn yields are an
accomplishment
While
High soybean yields are an
accident
Now We Know Better!
• Still, it’s clear that managing soybean within
our weather and soils will disappoint
sometimes
• But, the US remains a good place to grow
soybeans, and with continued attention to
genetics and inputs, we can continue to
compete
Seedfill Monitoring in Soybean
• As a pilot in 2005, we are going to take
weekly samples of soybean pods from
25-30 plants
• Dry and thresh to determine seed wt
per plant
• Relate ΔDW to temperature, moisture,
and solar radiation during past week
• Care to join us? ednaf@uiuc.edu
Thank You