Drought Stress and
Ontario Soybean
Yields: Unravelling the
Mystery
Hugh Earl, U of G
Horst Bohner, OMAFRA
160.6 bu/ac
Kip Cullers
171.8 bu/ac
Randy Dowdy
106.3 bu/ac
Robert and
Jason Lakey
Illinois
214.7 Bushel Yields: Coming Soon to a
Field Near You?
…soybeans can potentially produce hundreds
of pods per plant. If every node on every
branch produced multiple racemes and every
raceme produced multiple flowers, a soybean
plant can have a thousand potential pod sites.
Rain makes grain!
Where do High Yields Come From?
Basic principles of yield determination are more or less
universal across grain crops.
Agronomic decisions should be made with a clear
understanding of how yield is determined from a crop
physiology standpoint.
There are many persistent misconceptions about how
crops “work”.
Why Does Yield Vary So Much?
True Causes of Large Yield Variations are Often
Unknown
The “most limiting factor” idea is not a
very complete model of crop yield
limitations!
Factors may be co-limiting
(interacting).
The current most limiting factor will
change over the season, and even
over a single day.
Crop yield determination is much more
complicated than can be described
with this model.
Water Stress in Ontario Soybean:
Are we losing yield to water stress? If so, how much?
Uncertainties
How much of the in-season rainfall do we get to use?
To what extent can soil water depletion delay the onset
of stress during dry periods?
Does dry soil at any point in the root profile constitute a
water stress?
Quantifying Yield Lost to Drought Stress
1. Quantify yield reductions due to water stress
under naturally-occurring (rainfed) conditions
Compare to yield under water-replete (irrigated)
conditions
2. Identify the specific aspects of crop growth
and yield formation impacted by water stress
Interception of solar radiation, biomass
production, pods per unit area, seeds per pod,
seed size
Past Studies:
•Yield more sensitive to stress during pod elongation and
seed fill. Less sensitive to early season stress.Shaw and Lang, 1966; Doss et al., 1974; Andriani et al., 1991; Foroud et al., 1993
• Pods per unit area most sensitive yield component, but
late-season stresses can also reduce seed size.Sionit and Kramer, 1977; Korte et al.,1983; Brevedan and Egli, 2003
• Late-season stress leads to early canopy senescence,
shortening the seed fill period.Korte et al., 1983; Specht et al., 1986; Foroud et al., 1993
Methods:
S
S
S
25 m
25 m
25 m
12.5 mDry
Dry
Dry
Dry
Wet
Wet
Wet
Wet
~33 m
S
Solid set sprinkler, 180
Final seed yield and yield
components
Buffered in-season dry
matter harvests
2009
Solid set irrigation
4 replications
Methods:
2010 onward
Hose-pull boom cart
4 replications
B B406 412B B
405 411B B
404 410B B
403 409B B
402 408B B
401 407B BB BB BB BB BB BB BB BB BB B
306 312B B
305 311B B
304 310B B
303 309B B
302 308B B
301 307B B
206 212B B
205 211B B
204 210B B
203 209B B
202 208B B
201 207B BB BB BB BB BB BB BB BB BB B
106 112B B
105 111B B
104 110B B
103 109B B
102 108B B
101 107B B
10 b
uff
er
plo
ts10 b
uff
er
plo
ts
Year 1 (2009)
-5
0
5
10
15
20
0
50
100
150
200
250
300
350
400
450
500
0 25 50 75 100 125 Weekly
tem
pera
ture
devia
tio
n f
rom
10
-yr
avera
ge (
°C)
Pre
cip
itati
on
(m
m)
Days after planting
Cumulative precipitation + irrigation
Cumulative precipitation
10-year average cumulative precipitation
Year 1 (2009)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 25 50 75 100 125
Ca
no
py in
terc
ep
tan
ce
of s
ola
r ra
dia
tio
n
Days after planting
Irrigated
Rainfed
0
100
200
300
400
500
600
700
800
900
0 25 50 75 100 125
Ab
ove-g
rou
nd
dry
matt
er
(g m
-2)
Days after planting
Irrigated
Rainfed
yield yield pods m-2 seeds pod-1 100-seed wt
bu acre-1 kg ha-1 g
Irrigated 55.2 3700 898 2.38 17.3
Rainfed 50.2 3369 853 2.40 16.5
P-value 0.03 0.03 0.28 0.92 0.15
Irrigated / Rainfed 1.098 1.098 = 1.052 x 0.995 x 1.047
Year 2 (2010)
-5
0
5
10
15
20
0
50
100
150
200
250
300
350
400
450
500
0 25 50 75 100 125
Weekly
tem
pera
ture
devia
tio
n f
rom
10-y
r avera
ge (
°C)
Pre
cip
itati
on
(m
m)
Days after planting
Cumulative precipitation + irrigation
Cumulative precipitation
10-year average cumulative precipitation
Year 2 (2010)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 25 50 75 100 125
Ca
no
py in
terc
ep
tan
ce
of
so
lar
rad
iati
on
Days after planting
Irrigated
Rainfed
P < 0.01
0
100
200
300
400
500
600
700
800
900
0 25 50 75 100 125
Ab
ov
e-g
rou
nd
dry
ma
tte
r (g
m-2
)
Days after planting
Irrigated
Rainfed
P < 0.001
yield yield pods m-2 seeds pod-1 100-seed wt
bu acre-1 kg ha-1 g
Irrigated 58.1 3899 1005 2.39 16.3
Rainfed 53.7 3598 933 2.52 15.3
P-value 0.007 0.007 0.28 0.44 0.07
Irrigated / Rainfed 1.084 1.084 = 1.078 x 0.951 x 1.066
Year 3 (2011)
-5
0
5
10
15
20
0
50
100
150
200
250
300
350
400
450
500
0 25 50 75 100 125
Weekly
tem
pera
ture
devia
tio
n f
rom
10-y
r avera
ge (
°C)
Pre
cip
itati
on
(m
m)
Days after planting
Cumulative precipitation + irrigation
Cumulative precipitation
10-year average cumulative precipitation
Year 3 (2011)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 25 50 75 100 125
Ca
no
py in
terc
ep
tan
ce
of
so
lar
rad
iati
on
Days after planting
Irrigated
Rainfed
P < 0.05
P < 0.05
P < 0.05
0
100
200
300
400
500
600
700
800
900
0 25 50 75 100 125
Ab
ov
e-g
rou
nd
dry
ma
tte
r (g
m-2
)
Days after planting
Irrigated
Rainfed
P < 0.05
P < 0.05
P < 0.05P < 0.05
yield yield pods m-2 seeds pod-1 100-seed wt
bu acre-1 kg ha-1 g
Irrigated 56.2 3768 923 2.51 14.0
Rainfed 45.5 3051 790 2.40 13.8
P-value 0.04 0.04 0.005 0.16 0.60
Irrigated / Rainfed 1.235 1.235 = 1.168 x 1.046 x 1.014
Canopy Senescence
Canopy Senescence
NDRE
Year 2009 2010 2011
Date Sep 8 Sep 1 Sep 12
DAP 113 97 101
Irrigated 0.272 0.218 0.219
Rainfed 0.214 0.166 0.154
P-value <0.01 <0.01 <0.05
Irrigated Rainfed
Rep 1
Rep 2
Rep 3
Rep 4
2009
Year 4 (2012)
-5
0
5
10
15
20
0
50
100
150
200
250
300
350
400
450
500
0 25 50 75 100 125
We
ek
ly T
em
pe
ratu
re A
no
maly
(°C
)
Cu
mu
lati
ve
Pre
cip
ita
tio
n (
mm
)
Days after Planting
Year 5 (2013)
-5
0
5
10
15
20
0
50
100
150
200
250
300
350
400
450
500
550
0 25 50 75 100 125
We
ek
ly T
em
pe
ratu
re A
no
maly
(°C
)
Cu
mu
lati
ve
Pre
cip
ita
tio
n (
mm
)
Days after Planting
Years 4 and 5 (2012 - 2013)
yield yield pods m-2
seeds pod-1
100-seed wt
bu acre-1
kg ha-1
g
2012
Irrigated 70.2 4714 1283 2.32 16.3
Rainfed 60.6 4064 1049 2.28 17.4
P-value <0.0001 <0.0001 <0.0001 0.92 0.15
Irrigated / Rainfed 1.160 1.160 = 1.223 x 1.018 x 0.937
2013
Irrigated 64.7 4343 1009 2.32 17.6
Rainfed 62.6 4200 1001 2.29 17.3
P-value 0.014 0.014 0.65 0.44 0.07
Irrigated / Rainfed 1.034 1.034 = 1.008 x 1.013 x 1.017
Mean responses across 15 varieties.
2009 – 2013 Summary
1. There was significant yield loss attributable
to water stress in all five years.
•Yield loss ranged from 3% to 24%.
•These estimates are probably conservative.
• Yield loss occurred even when the in-season
rainfall total exceeded the 10-yr average (2010,
2013), or when it equaled the 10-yr average
and was very well distributed (2009)
2. When yield losses were small, it was
sometimes difficult to parse the yield loss
amongst the various yield components.
• pods m-2 was the component most consistently
affected
3. Early canopy senescence was a consistent
feature of water stress
4. There were never any obvious visual
symptoms of stress, such as leaf wilting.
2009 – 2013 Summary
Water is not everything!
Year Rainfed Yield
Mg / ha
Irrigated Yield
Mg / ha
Increase from
irrigation
2009 3.37 3.70 9.8%
2010 3.60 3.90 8.3%
2011 3.05 3.77 23.6%
2012 4.06 4.71 16.0%
2013 4.20 4.34 3.3%
Average 12.2%
24.9%
Highest yields on this farm: 5.4 Mg / ha
Highest yields in Ontario: 6.7 Mg / ha
When during the season is yield determined?
The Critical Developmental Stage is the one where the
most Variable Yield Component is Determined.
For soybean:
Yield = pods per m2
x seeds per pod
x mass per seed
What determines pod number?
Pod number (and therefore seed number) is
determined by the plant growth rate during the
critical period (R2 to R5).
Pod number is NOT a direct function of plant size.
It’s now how big the crop is – what matters is how
fast it is growing.
Maximizing pod numbers is mostly a matter of
maximizing crop growth rate during the critical
period.
(Data of Vega, 2001)
Think at the Crop Scale
The Plant Community (“Crop Canopy”) is more
Relevant than Individual Plants. Think on a Ground
Area Basis.
We measure yield per unit area, not on a single plant
basis. Plant size is (almost) irrelevant.
Many important processes that determine yield can
only be properly understood at the crop canopy (plant
community) scale.
For maize and a few other crops, individual plant size
can be important. For soybean it is very unimportant.
Plant size is unimportant in soybean
• Maize is prone to barrenness when there is insufficient assimilate flux
prior to anthesis (i.e., plants are too small).
• Species with a larger number of fruiting structures, including soybean
are much less sensitive to plant size.
(Vega and Sadras, 2003)
Soybean is insensitive to seeding rate
0
20
40
60
80
100
120
0 100 200 300 400 500
Seeding rate (thousands per acre)
Yie
ld (
pe
rce
nt
of
ma
xim
um
)
2005, early
2005, late
2006, early
2006, late
k = 0.0191
Response of soybean yield to seeding rate.
Radiation Capture
The Crop Growth Rate is Primarily Determined by
Radiation Capture
X X RUE =Biomass
Radiation Capture
time
Radiation Capture
The crop growth rate during the critical period (R2 - R5) determines final
pod numbers Maximizing the crop growth rate requires complete
interception of sunlight.
Row Width still Matters
Bu/ac1) 30” no-till (130 000) 65.3
2) 30” managed (130 000) 69.8
3) 30” managed (170 000) 69.4
4) 15” no-till (170 000) 69.5
5) 15” managed (170 000) 69.9
Managed = 180 lbs/ac MESZ and 6-24-24 (2X2), 3 gallons
6-24-6 IF, spring strip tillage, foliar fungicide and feeding.
Elora 2016, P = 10 ppm, K = 96 ppm
Closing the Yield Gap
Bu/ac1) 30” no-till (130 000) 62.0
2) 30” managed (130 000) 63.5
3) 30” managed (170 000) 64.9
4) 15” no-till (170 000) 65.4
5) 15” managed (170 000) 67.0
Managed = 180 lbs/ac MESZ and 6-24-24 (2X2), 3 gallons
6-24-6 IF, spring strip tillage, foliar fungicide and feeding.
Lucan 2016, P = 14 ppm, K = 109 ppm
Closing the Yield Gap
Wide rows are not a good choice
if rows do not fill by R3
y = 0.4732x - 6.7867
Variety Selection is Key
y = 1.125x - 86.232
Bu/ac
1) 15” no-till (Variety A) 69.5
2) 30” managed (Variety A) 69.8
3) 15” no-till (Variety B) 75.7
4) 30” managed (Variety B) 74.7
5) 15” no-till (Variety C) 81.8
6) 30” managed (Variety C) 81.5
Good Variety Choice Equals Profit
Managed = 180 lbs/ac MESZ and 6-24-24 (2X2), 3 gallons
6-24-6 IF, spring strip tillage, foliar fungicide and feeding.
Elora 2016, P = 10 ppm, K = 96 ppm
171.8 bu/ac
Randy Dowdy
Good Soil Fertility is Essential
Bu/ac
1) Check 64
2) MESZ (375 lbs/ac) 72
3) MESZ (375 lbs/ac + 70
333 lbs/ac potash)
Mega Fertilizer
Bornholm 2016, P = 17, K = 98
Bu/ac
1) Check 64
2) MESZ (375 lbs/ac) 72
3) MESZ (375 lbs/ac + 70
333 lbs/ac potash)
4) Trt. 2+3+ N (150 lbs/ac) 70
Mega Fertilizer
Bornholm 2016, P = 17, K = 98
Yiel
d (
bu
/ac)
CORN
SOY
WHEAT
Yield Trends in Ontario of Corn, Soybean, Winter Wheat1981-2015
Yiel
d (
bu
/ac)
CORN
SOY
WHEAT
Yield Trends in Ontario of Corn, Soybean, Winter Wheat1981-2015
35 lbs P2O5, 25 K2O
30 lbs P2O5, 18 K2O
28 lbs P2O5, 46 K2O
80% yield increase
63 lbs P2O5, 45 K2O
65% yield increase
50 lbs P2O5, 30 K2O
35% yield increase
37 lbs P2O5, 61 K2O
Hooker, UG2013
No P appliedSoil test P = 7 ppm
P broadcast applied
Soybean response to P and K fertilizer
Starter (per ac)Approx. background soil test P and K (ppm)
ANOVA across background Low P
Low KLow PHigh K
High PHigh K
bu/ac
No Fertilizer 56 b
6-24-6 @ 3 gal (IF) 58 ab
MAP @ 100 lbs (2x2) 59 a
0-0-60 @ 80 lbs (2x2) 58 ab
6-28-28 @ 90 lbs (2x2) 59 a
6-28-28 @ 180 lbs (2x2) 60 a
Soybean yield response to background fertility and starter fertilizerLucan (2014-2016)
n=12Mean separation within column statistically significant at P=0.05 @cropdoc2 #SWAC17
NOTABLE NOTE:180 lbs 6-28-28 = 50 lbs of P2O5 or K2O Current rec = 20 lbs/ac P2O5, 30 lbs/ac K2O
Starter (per ac)Approx. background soil test P and K (ppm)
ANOVA across background Low P
Low KLow PHigh K
High PHigh K
bu/ac
No Fertilizer 56 b 56 de
6-24-6 @ 3 gal (IF) 58 ab 58 cd
MAP @ 100 lbs (2x2) 59 a 62 ab
0-0-60 @ 80 lbs (2x2) 58 ab 55 e
6-28-28 @ 90 lbs (2x2) 59 a 59 bc
6-28-28 @ 180 lbs (2x2) 60 a 62 a
Soybean yield response to background fertility and starter fertilizerLucan (2014-2016)
n=12Mean separation within column statistically significant at P=0.05 @cropdoc2 #SWAC17
Starter (per ac)Approx. background soil test P and K (ppm)
ANOVA across background Low P
Low KLow PHigh K
High PHigh K
bu/ac
No Fertilizer 56 b 56 de 63 a <0.05
6-24-6 @ 3 gal (IF) 58 ab 58 cd 64 a <0.05
MAP @ 100 lbs (2x2) 59 a 62 ab 64 a <0.05
0-0-60 @ 80 lbs (2x2) 58 ab 55 e 64 a <0.05
6-28-28 @ 90 lbs (2x2) 59 a 59 bc 64 a <0.05
6-28-28 @ 180 lbs (2x2) 60 a 62 a 63 a ns
Soybean yield response to background fertility and starter fertilizerLucan (2014-2016)
n=12, P = 10, K = 129 (low) and P = 27, K = 166 (high)Mean separation within column statistically significant at P=0.05 @cropdoc2 #SWAC17
Starter (per ac)Background treatment
Low PLow K
High PLow K
Low PHigh K
High PHigh K
bu/ac
No starter 53c 55b 55c 60a
6-24-6 in-furrow 55b 56b 56b 61a
MAP @ 100 lbs (2x2) 55b 56b 58a 61a
0-0-60 @ 80 lbs (2x2) 54b 58a 54c 60a
6-28-28 @ 90-180 lbs (2x2) 57a 59a 58a 61a
Soybean yield response to background fertility and starter fertilizerAverage across 17 site-years
Mean separation within column statistically significant at P=0.05@cropdoc2 #SWAC17
Fertility Summary
• Fertility is KEY to high yields!!!
– Soil health includes good fertility
– But it’s not as simple as applying high rates
of fertilizer
• Building soil test values to a reasonable level
provides more consistent and higher yields
• Low soil tests reduces yield by 4 – 7 bu/ac
214.7 Bushel Yields: Coming Soon to a
Field Near You?… one important step was spoon feeding N, P and K through
the drip irrigation based on growth stage. They applied 610
lbs. of nitrogen, 40 lbs. of phosphate and 200 lbs. of potash,
and adequate micronutrients were added at planting.
2016 SMaRT Trial Locations
KTS Starter Fertilizer
Broadcast Gypsum
Planting Rate
ILeVO
Field Rolling
Prescription Foliar Fertilizer
White Mold Fungicide Comparison
Intensive Management
Radiate
Blackmax 22
2016 Prescription foliar fertilizer trial locations
Field-specific prescription foliar fertilizer mixtures were
compared to an unfertilized control at nine locations in 2016.
Composite soil samples were collected from the trial area in
the spring of 2016 and sent to Midwest Labs for testing.
The field-specific prescription foliar fertilizer mixtures were
developed by AgroLiquid and based on soil test nutrient
levels.
AgroLiquid also determined the application timing: V4 for row
spacing of 15” or less and R1 where row spacing was greater
that 15”.
Prescription foliar fertilizer trial
Location O.M. P K Mg Ca pH CEC S Zn Mn
% ------------ ppm ------------ 1:1meq/ 100g ------- ppm ------
Cass 1.4 93 172 93 1057 6.7 6.5 8 2.1 4Ionia 2.1 50 152 241 1243 6.6 9.3 8 1.9 7Gratiot 2.8 27 165 248 1593 7 10.6 17 2.4 4St. Joseph 1 64 99 79 665 6 5.1 23 1.8 7Van Buren 1.5 29 162 81 719 5.9 5.7 13 1.4 16Lenawee 2 2.1 99 177 179 975 6.1 8 10 1.7 3 Monroe 2.4 49 177 193 1131 6 9.2 13 2.5 4Lenawee 1 2.7 16 141 254 1712 6.2 12.6 15 1.4 5Sanilac 3.7 31 244 227 2460 7.9 14.9 20 1.8 2
Soil test levels at the 2016 prescription foliar fertilizer trial locations
Bold figures indicate low or very low soil test levels.
Location Foliar fertilizer products and application ratesFertilizer
cost$/ac
Cass 1.5 gal/ac of fertiRain, and 1 qt/acre of Manganese $19.10 Ionia 1.5 gal/ac of fertiRain, 2 qt/acre of Manganese, and 2 qt/ac of LiberateCa $28.70 Gratiot 1.5 gal/ac of fertiRain, and 1 qt/acre of Manganese $19.10 St. Joseph 1.5 gal/ac of fertiRain, and 1 qt/acre of Manganese $19.10 Van Buren 1.5 gal/ac of fertiRain, 1 qt/acre of Manganese, and 1 qt/ac of LiberateCa $19.50 Lenawee 2 1.5 gal/ac of fertiRain, 2 qt/acre of Manganese, and 2 qt/ac of LiberateCa $28.70 Monroe 1.5 gal/ac of fertiRain, 2 qt/acre of Manganese, and 1 qt/ac of LiberateCa $20.80 Lenawee 1 1 gal/ac of fertiRain, 1 gal/ac of Sure-K, and 2 qt/acre of Manganese $21.40 Sanilac 1.5 gal/ac of fertiRain, and 1 qt/acre of Manganese $19.10
Prescription foliar fertilizer products, application rates and costs for
each location
Analyses of the foliar fertilizer products are listed below:fertiRain: 12-3-3 plus 1.5% S, 0.10% Fe, 0.05% Mn, and 0.10% Zn LiberateCa: 3% calcium from calcium sulfate Manganese: 4% manganese from manganese sulfateSure-K: 2-1-6
*1.5 *1.4
1.20.8 0.5
0.1
-0.1-0.5
-1.5
0.3
-3
-2
-1
0
1
2
3
4
Yie
ld d
iffe
rence
(bu/a
c)
Lowest breakeven yield increase for all sites (2.1 bu/ac)
* The yield difference was statistically significant at these locations
Yield difference produced by a single application of a
prescription foliar fertilizer in 2016
The prescription foliar fertilizer treatment increased soybean yields at two of nine locations in 2016.
However, the yield increases were not large enough to cover the cost of the foliar fertilizer ($19.10 to $28.70 per acre).
The lack of a profitable response to foliar fertilization is most likely due to the medium to high soil test levels for many of the nutrients in the trials.
However, soil test levels for sulfur were low at 3 sites and manganese was very low to low at 8 sites.
Prescription foliar fertilizer trial
Production Practices That Often Have
A Large (5+ Bu/A) Impact on Yield
• Planting Date
• Fertility
• Variety Selection and Placement
• Drainage and Compaction Management
• Insect, Disease, and Weed Management
Production Practices That Often Have
A Moderate (2 to 5 Bu/A) Impact on
Yield
• Foliar Fungicides
• Seed Treatments
• Residue Managment
• Crop Rotation
– Larger first year effect
• Row Spacing
Production Practices That Often
Have A Small (<2 Bu/A) Impact on
Yield
• Seeding Rate and Equipment
• Inoculants
• Micronutrients
– Can be large under the right circumstances
– More important as yield level increases