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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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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?
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)