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Effectiveness of Sidedressed
Fluid Potassium Fertilizer
in Corn and Soybean
Antonio P. Mallarino
Department of Agronomy
Iowa State University
Extension and OutreachIOWA STATE UNIVERSITY
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Extension and OutreachIOWA STATE UNIVERSITY
Plant Roots and P - K Uptake
• P and K are much less mobile than nitrate,
need to reach roots by diffusion from a
very short distance
• Actively growing root systems with fine
roots is key for uptake of both, and P is
especially needed for early growth
• Banding could help with
- High soil “fixing” capacity
- Soil conditions limiting root/seedling growth
- Cold, compaction, root diseases or insects
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Extension and OutreachIOWA STATE UNIVERSITY
Preplant K Placement in Corn & Soybean
• Iowa research since the 1960s has shown
no difference between K fertilization
broadcast, banded preplant, or banded
with the planter with few exceptions
• Deep banding (4 to 6 inches)
- Ridge-till, a must for corn, also found by G.
Rehm in MN in late 1980s and early 1990s
- No-till and strip-tillage, sometimes for corn,
mainly with dry topsoil June to early July IF
there is moisture in the band zone, doubtful
payback
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Extension and OutreachIOWA STATE UNIVERSITY
Not Surprising with Iowa Soils & Climate
• Little or no P or K “fixation”; retention of P
and K by soil doesn’t mean fixation
• Good soils allow for large root systems with
many fine roots for P and K uptake
• Usually humid spring weather
• Cold/wet soil early but,
- Need to plant so early?
- Starter P in-furrow or 2x2” is a cost-effective fix,
complements broadcast preplant application
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Extension and OutreachIOWA STATE UNIVERSITY
Sidedressing for P and K?
• Fluid N sidedressing for corn is common
- Complements preplant fertilization
- Much research has been conducted
• Sidedressing of P fertilizer, fluid or dry, is
unlikely to work, crops need P very early
- Cell multiplication and division
- New and more leaves
- Grain sink is determined early
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Extension and OutreachIOWA STATE UNIVERSITY
Sidedressing for K?
• Doubts, scarce research without irrigation
or with different preplant K application rates
- Not much K needed early, large uptake later on
- Not much K leaching except in sandy soils
- No “true” starter K effect, as it is with N and P
• As a split application can be helpful in some
conditions or serve as a rescue option
- Need soil moisture for uptake, injecting fluid K
with relatively new low-salt potassium acetate
may be the best option
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Extension and OutreachIOWA STATE UNIVERSITY
Trials and Soils
• Twelve 2-year trials with corn-soybean
rotations
- One no-till, others tillage for corn
- Six began in 2017 and six in 2018
• Six soil series
- Central, N, NE, S, SE, SW Iowa
- Poorly drained to well drained
- Texture loam, clay loam, or silty clay loam
- Organic matter 3.2 to 4.5%
- pH 5.8 to 6.7
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Extension and OutreachIOWA STATE UNIVERSITY
Trials and Treatments
• Five preplant K treatments in large plots,
two K sidedress treatments in subplots,
four replications in blocks
• Used established trials, each with useful
similar previous management except for K
fertilization
• Each block (replication) had four large low-
testing plots (no K application for 6-8 years)
and one high-testing plot with history of
annual K applications
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Extension and OutreachIOWA STATE UNIVERSITY
Potassium Treatments
• Preplant K treatments only to corn (1st year)
- 4 broadcast rates (0, 45, 90, 135 lb K2O/acre)
2-3 weeks before planting randomized to the
four large low-testing plots of each block
- No K to the high-test plot of each block
• Sidedress K treatments to both crops
- No/Yes fluid potassium acetate (0-0-24)
- 45 lb K2O/acre at the V5-V6 stage injected
between the rows (30-inch spacing) to a
depth of 3 to 4 inches
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Extension and OutreachIOWA STATE UNIVERSITY
Crop and Soil Measurements
• Soil-test K, 6-inch sampling depth
- Initial of low-testing and high-testing plots
- After corn harvest (before soybean) of plots
that didn’t get sidedressed K
• Leaf K concentrations
- Corn ear-leaf blades at R1 stage (silking)
- Top soybean trifoliate leaves at R2-R3
• Grain yield, K concentration and removal
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Extension and OutreachIOWA STATE UNIVERSITY
Corn 2017 Leaf K Concentration
SITE 1 - Central Iowa
0 45 90 135 HSTK
Le
af
K C
on
ce
ntr
atio
n (
%)
0.5
1.0
1.5
2.0
2.5
0 K sidedress45 K sidedress
SITE 2 - Southern Iowa
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
0 K sidedress45 K sidedress
SITE 3 - Southern Iowa
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
0 K sidedress45 K sidedress
SITE 4 - Northeast Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
Le
af
K C
on
ce
ntr
atio
n (
%)
0.5
1.0
1.5
2.0
2.5
0 K sidedress45 K sidedress
SITE 6 - Southwest Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
0 K sidedress45 K sidedress
SITE 5 - Northern Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
0 K sidedress45 K sidedress
Initial Soil-Test K Very Low
Initial Soil-Test K Low Initial Soil-Test K VL-Low
Initial Soil-Test K Low Initial Soil-Test K Low Initial Soil-Test K Low
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Extension and OutreachIOWA STATE UNIVERSITY
Corn 2017 Grain Yield
SITE 1 - Central Iowa
0 45 90 135 HSTK
Gra
in Y
ield
(bu/a
cre
)
125
150
175
200
225
250
275
0 K sidedress45 K sidedress
SITE 2 - Southern Iowa
0 45 90 135 HSTK
125
150
175
200
225
250
275
0 K sidedress45 K sidedress
SITE 3 - Southern Iowa
0 45 90 135 HSTK
125
150
175
200
225
250
275
0 K sidedress45 K sidedress
SITE 4 - Northeast Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
Gra
in Y
ield
(bu/a
cre
)
125
150
175
200
225
250
275
0 K sidedress45 K sidedress
SITE 5 - Northern Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
125
150
175
200
225
250
275
0 K sidedress45 K sidedress
SITE 6 - Southeast Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
125
150
175
200
225
250
275
0 K sidedress45 K sidedress
Initial Soil-Test K Very Low
Initial Soil-Test K Low Initial Soil-Test K VL-Low
Initial Soil-Test K Low Initial Soil-Test K Low Initial Soil-Test K Low
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Extension and OutreachIOWA STATE UNIVERSITY
Corn 2018 Leaf K Concentration
SITE 7 - Central Iowa
0 45 90 135 HSTK
Le
af
K C
on
ce
ntr
atio
n (
%)
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 8 - Southern Iowa
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 9 - Southern Iowa
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 10 - Northeast Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
Le
af
K C
on
ce
ntr
atio
n (
%)
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 12 - Southwest Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 11 - Northern Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
Initial Soil-Test K Very Low Initial Soil-Test K Low-Optimum Initial Soil-Test K Low
Initial Soil-Test K Very LowInitial Soil-Test K Low Initial Soil-Test K Low
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Extension and OutreachIOWA STATE UNIVERSITY
Corn 2018 Grain Yield
SITE 7 - Southern IA
0 45 90 135 HSTK
Gra
in Y
ield
(bu/a
cre
)
100
125
150
175
200
225
250
0 K sidedress45 K sidedress
SITE 8 - Southern IA
0 45 90 135 HSTK
100
125
150
175
200
225
250
0 K sidedress45 K sidedress
SITE 9 - Northeast IA
0 45 90 135 HSTK
100
125
150
175
200
225
250
0 K sidedress45 K sidedress
SITE 10 - Northern IA
Broadcast K Rate (lb K2O/acre)0 45 90 135 HSTK
Gra
in Y
ield
(bu/a
cre
)
100
125
150
175
200
225
250
0 K sidedress45 K sidedress
SITE 11 - Southeast IA
Broadcast K Rate (lb K2O/acre)0 45 90 135 HSTK
100
125
150
175
200
225
250
0 K sidedress45 K sidedress
SITE 12 - Southwest IA
Broadcast K Rate (lb K2O/acre)0 45 90 135 HSTK
100
125
150
175
200
225
250
0 K sidedress45 K sidedress
Initial Soil-Test K Very Low Initial Soil-Test K Low-Optimum Initial Soil-Test K Low
Initial Soil-Test K Very LowInitial Soil-Test K Low Initial Soil-Test K Low
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Extension and OutreachIOWA STATE UNIVERSITY
Soybean 2018 Leaf K Concentration
SITE 1 - Central Iowa
0 45 90 135 HSTK
Lea
f K
Conce
ntr
ation (
%)
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 2 - Southern Iowa
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 3 - Southern Iowa
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 4 - Northeast Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
Lea
f K
Conce
ntr
ation (
%)
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 6 - Southwest Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 5 - Northern Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
Rates Before Previous CornRates Before Previous Corn Rates Before Previous Corn
Rates Before Previous Corn Rates Before Previous Corn Rates Before Previous Corn
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Extension and OutreachIOWA STATE UNIVERSITY
Soybean 2018 Grain Yield
SITE 1 - Central Iowa
0 45 90 135 HSTK
Gra
in Y
ield
(bu
/acre
)
40
45
50
55
60
65
70
75
0 K sidedress45 K sidedress
SITE 2 - Southern Iowa
0 45 90 135 HSTK
40
45
50
55
60
65
70
75
0 K sidedress45 K sidedress
SITE 3 - Southern Iowa
0 45 90 135 HSTK
40
45
50
55
60
65
70
75
0 K sidedress45 K sidedress
SITE 4 - Northeast Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
Gra
in Y
ield
(bu
/acre
)
40
45
50
55
60
65
70
75
0 K sidedress45 K sidedress
SITE 5 - Northern Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
40
45
50
55
60
65
70
75
0 K sidedress45 K sidedress
SITE 6 - Southeast Iowa
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
40
45
50
55
60
65
70
75
0 K sidedress45 K sidedress
Rates Before Previous CornRates Before Previous Corn Rates Before Previous Corn
Rates Before Previous Corn Rates Before Previous Corn Rates Before Previous Corn
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Extension and OutreachIOWA STATE UNIVERSITY
Soybean 2019 Leaf K Concentration
SITE 7 - Southern IA
0 45 90 135 HSTK
Le
af
K C
on
ce
ntr
atio
n (
%)
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 8 - Southern IA
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 9 - Northeast IA
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 10 - Northern IA
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
Le
af
K C
on
ce
ntr
atio
n (
%)
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 12 - Southwest IA
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
SITE 11 - Southeast IA
Broadcast K Rate (lb K2O/acre)
0 45 90 135 HSTK
0.5
1.0
1.5
2.0
2.5
3.0
0 K sidedress45 K sidedress
Rates Before Previous CornRates Before Previous Corn Rates Before Previous Corn
Rates Before Previous Corn Rates Before Previous Corn Rates Before Previous Corn
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Extension and OutreachIOWA STATE UNIVERSITY
Soybean 2019 Grain Yield
SITE 7 - Southern IA
0 45 90 135 HSTK
Gra
in Y
ield
(b
u/a
cre
)
40
45
50
55
60
65
70
75
80
0 K sidedress45 K sidedress
SITE 8 - Southern IA
0 45 90 135 HSTK
40
45
50
55
60
65
70
75
80
0 K sidedress45 K sidedress
SITE 9 - Northeast IA
0 45 90 135 HSTK
40
45
50
55
60
65
70
75
80
0 K sidedress45 K sidedress
SITE 10 - Northern IA
Broadcast K Rate (lb K2O/acre)0 45 90 135 HSTK
Gra
in Y
ield
(b
u/a
cre
)
40
45
50
55
60
65
70
75
80
0 K sidedress45 K sidedress
SITE 11 - Southeast IA
Broadcast K Rate (lb K2O/acre)0 45 90 135 HSTK
40
45
50
55
60
65
70
75
80
0 K sidedress45 K sidedress
SITE 12 - Southwest IA
Broadcast K Rate (lb K2O/acre)0 45 90 135 HSTK
40
45
50
55
60
65
70
75
80
0 K sidedress45 K sidedress
Rates Before Previous CornRates Before Previous Corn Rates Before Previous Corn
Rates Before Previous Corn Rates Before Previous Corn Rates Before Previous Corn
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Extension and OutreachIOWA STATE UNIVERSITY
Corn Yield, 45-lb Preplant vs Sidedress
2017 - Averages of 6 Sites
Broadcast K Rate (lb K2O/acre)0 45 90 135
Gra
in Y
ield
(b
u/a
cre
)
170
180
190
200
210
220
2018 - Averages of 6 Sites
Broadcast K Rate (lb K2O/acre)0 45 90 135
Gra
in Y
ield
(b
u/a
cre
)170
180
190
200
210
22045 K
2O sidedress
45 K2O sidedress
No K sidedressNo K sidedress
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Extension and OutreachIOWA STATE UNIVERSITY
Averages for 2nd-Year Soybean
2018 - Averages of 6 Sites
Broadcast K Rate for 1st-YearCorn (lb K2O/acre)
0 45 90 135
Gra
in Y
ield
(b
u/a
cre
)
50
55
60
65
702019 - Averages of 6 Sites
Broadcast K Rate for 1st-YearCorn (lb K2O/acre)
0 45 90 135
Gra
in Y
ield
(b
u/a
cre
)
50
55
60
65
70
45 K2O sidedress to
corn and soybean
45 K2O sidedress to
corn and soybean
No K sidedress
No K sidedress
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Extension and OutreachIOWA STATE UNIVERSITY
Conclusions
• Sidedressing liquid K fertilizer doesn’t
increase corn yield with recommended
preplant broadcast K fertilization rates
- Less efficient than a preplant similar rate
- Good rescue option with insufficient
preplant K
• I doubt will get different results but:
- Different sidedress K rates?
- Dribbling to inter-row or with Y-drop?
- Sidedressing N and K together?
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Extension and OutreachIOWA STATE UNIVERSITY
www.agronext.iastate.edu/soilfertility/
THANK YOU
Funding by- Fluid Fertilizer Foundation
- Pioneer (Corteva Agriscience)
In-Kind Contributions- The Andersons (2017)
- Nachurs (2018, 2019)