Corn and Soybean Yield Responses to
Micronutrients and Relationships
with Soil and Tissue Tests
Antonio P. Mallarino
Department of Agronomy
Iowa State University
Recent Interest in Micronutrients

Good grain prices, could afford apply
"just in case" to maximize yield

Next limiting step with lime, P and K
issues "solved"; higher yield levels

Word of deficiencies in other states

Talk of Mn/Glyphosate issue in Indiana

Several micros, many products
available, dry and liquid sources, many
nutrient "packs" being offered
IOWA STATE UNIVERSITY
Extension and Outreach
Micronutrients for Crops

Essential but needed in very small
amounts

Boron (B), Chlorine (Cl), Copper (Cu),
Chloride (Cl), Iron (Fe), Manganese
(Mn), Molybdenum (Mo), Nickel (Ni),
Zinc (Zn) [cobalt?]

Large variation in crops sensitivity

Is fertilization needed? Not necessarily
if soil supplies sufficient amounts
IOWA STATE UNIVERSITY
Extension and Outreach
Micros Deficiencies More Likely
Micronutrient
Soil Conditions
Crop
Boron (B)
Sandy or highly weathered soils
low in organic matter, drought
Alfalfa, clovers
Copper (Cu)
Acid organic or very sandy soils
Wheat, oats, corn
Iron (Fe)
Manganese (Mn)
Zinc (Zn)
Molybdenum (Mo)
Calcareous soils pH (> 7.0)
Organic soil with high pH (> 5.8), Soybean, wheat,
Calcareous soils pH (> 7.0)
oats, sugar beets
Sandy or organic, low organic matter
Corn, sorghum
due to erosion, calcareous soils
Very acid soils (< 5.5 or so)
Adapted from several extension publications in the North-Central region
IOWA STATE UNIVERSITY
Extension and Outreach
Soybean
Legumes
Micros Removal and Yield Level in Iowa
Removed in Grain (lb/acre)
0.30
Copper
Boron
Manganese
Zinc
0.25
0.20
0.15
0.10
0.05
0.00
50
100
200
250
50
100
150
200
250
50
100
150
200
250
50
100
150
200
250
Corn Yield (bu/acre)
Corn Yield (bu/acre)
Corn Yield (bu/acre)
Corn Yield (bu/acre)
Boron
Copper
Manganese
Zinc
20 30 40 50 60 70 80
20 30 40 50 60 70 80
20 30 40 50 60 70 80
20 30 40 50 60 70 80
Soybean Yield (bu/acre)
Soybean Yield (bu/acre)
Soybean Yield (bu/acre)
Soybean Yield (bu/acre)
0.25
Removed in Grain (lb/acre)
150
0.20
0.15
0.10
0.05
0.00
IOWA STATE UNIVERSITY
Extension and Outreach
Manures Supplies Micronutrients!
Manure source
Dairy solid
Swine solid
Poultry
Dairy liquid
Swine liquid
Iron Manganese Boron Zinc Copper
-------------------- lb/ton as-is ----------------------0.5
0.06
0.01
0.03
0.01
19.0
1.09
0.04
0.79
0.50
3.0
0.61
0.08
0.48
0.66
------------------- lb/1000 gal ---------------------0.9
0.11
0.03
0.11
0.12
2.5
0.23
0.06
1.03
0.62
Kent Martin, Crops and Soils Specialist, KSU
IOWA STATE UNIVERSITY
Extension and Outreach
Problems with Micros Diagnosis

Deficiencies in the region have been
isolated and poorly documented except
for Fe and Mn in some areas

Difficult soil or tissue testing calibration
research: Many micros & factors, costs

Soil testing has been much less useful
than for P, K, or pH

Tissue testing has not been more reliable
−
−
Testing early enough to correct deficiency?
Little or not calibration work
IOWA STATE UNIVERSITY
Extension and Outreach
Many Micronutrient Sources

Boron: Sodium tetraborate and
pentaborate, boric acid

Cu, Fe, Mn, Mo, Zn:
− Inorganic oxides and sulfates
− Chelates various (EDTA, EDDHA)
− Organic complexes (paper, citrus, and
sugar industry by-products)

Water solubility of mineral sources, Fe
chelates good for soil application, price
IOWA STATE UNIVERSITY
Extension and Outreach
Zinc Deficiency in Corn
IOWA STATE UNIVERSITY
Extension and Outreach
Zinc Deficiencies in the Region



Deficiencies sometimes observed in
corn, but not in soybean
Approximately similar interpretations in
the region for the DTPA soil test for Zn
and recommendations
Apply Zn with less than 0.8 to 1.0 ppm
5 to 10 lb Zn/acre broadcast
− 1 to 2 lb/acre with the planter
−

But large soil-test failure at predicting
response even at very low levels (IA, MN)
IOWA STATE UNIVERSITY
Extension and Outreach
Manganese & Glyphosate in Soybean
Photo: Don Huber, IN, 2005
IOWA STATE UNIVERSITY
Extension and Outreach
Manganese in Soybean

Deficiencies observed for decades east
of the Mississippi River, mainly in IN,OH
−
−
−

More frequent or worse with RR
Variable responses to application to soil or
foliage mixed with glyphoste or not
More consistent response with banded Mn
with starter (Indiana work)
No evidence of deficiency in IA, MN, ND
−
−
No response applied to the soil or foliage
No evidence of the glyphosate problem
IOWA STATE UNIVERSITY
Extension and Outreach
Iron Chlorosis in Soybean
IOWA STATE UNIVERSITY
Extension and Outreach
Iron Fertilization for Soybean

No general agreement about
recommendations mixed results in various
states with unclear cost-benefit impact

Foliar fertilization generally unsuccessful,
some greening but no yield response in IA,
KS and isolated small responses in MN, ND

Mixed results for banded application to the
soil, some success with seed-placed chelated
iron mainly EDDHA (KS, MN, ND)

Choosing tolerant varieties or planting corn
seems to be the safest remedy
IOWA STATE UNIVERSITY
Extension and Outreach
Other Micronutrients

Deficiencies for other micronutrients
seldom seen in corn or soybean

Soybean molybdenum deficiency in
very acidic soils (<5.5)
− In a few states, 1960s to 1980s
− Response mainly to seed placement
− But the deficiency is corrected by
obviously needed liming
IOWA STATE UNIVERSITY
Extension and Outreach
Foliar Spray Research 2012-2014

46 soybean and 10 corn plot trials, 35 at
farmers' fields

B, Cu, Mn, Zn, and the mixture; 4 reps

Sprayed at V5-V6 and again at V8-V10 in
corn or R2-R3 in soybean

Total amount applied:
−
−
−
−
Boric acid (Max-In B), 0.16 lb B /acre
EDTA Cu (Max-In Cu), 0.08 lb Cu /acre
EDTA Zn (MicroBolt Zn), 0.33 lb Mn/acre
EDTA Mn (MicroBolt Mn), 0.50 lb Zn/acre
IOWA STATE UNIVERSITY
Extension and Outreach
Foliar Spray Strip Trials, 2012 & 2014

ISU field specialists on-farm project

26 corn and soybean strip trials
−
North, NW, and SW Iowa
9 with corn
17 with soybean
−
3 to 5 replications
−
−

Sprayed a mixture of B, Mn, and Zn
−
−
−
One application at V6 to V8 stage
1 pint/acre Max-In B
1 quart/acre Max-In B & ZMB (0.1% B, 3%Mn,
4% Zn, 3.6% S)
IOWA STATE UNIVERSITY
Extension and Outreach
Micros To Soil Research 2012-2014

8 trials, 3 years each, 4 began with corn
and 4 with soybean, 4 to 5 replications

Treatments
− B, Mn, Zn planter band with MAP
− Mixture band or broadcast with MAP

Solid granulated fertilizers
−
−
−
Boron: NuBor 10 (boric acid, 1.5% S):
− banded 0.5 lb B/ac, broadcast 2 lb B/ac
Mn: Broadman20 (12% S), 5 lb Mn/ac
Zn: EZ20 (14% S), 5 lb Zn/ac
IOWA STATE UNIVERSITY
Extension and Outreach
Grain Yield Response Results

56 foliar fertilization plot trials
−
−

26 foliar fertilization strip trials
−
−

One soybean yield increase
One corn yield decrease
Fertilization to soil: 8 fields, 3 years each
−

No grain yield increase at any trial
Yield decrease at one soybean trial from
Cu, Zn, and the mixture
No yield increase or decrease at any trial
Yield levels: - Soybean 20-74 bu, avg 55
- Corn 144 to 255 bu, avg 200
IOWA STATE UNIVERSITY
Extension and Outreach
Foliar, Soybean Yield Averages
2012, 22 sites
Control
B ns
Cu ns
2013, 20 sites
Mn ns
Zn ns
Soybean Yield (bu/acre)
50
Mixture
P <0.05
48
46
P <0.05
44
42
40
Results for three trials in 2014 are not shown
IOWA STATE UNIVERSITY
Extension and Outreach
Min
20
Max
74
Avg
49
Soybean Grain Yield (bu/acre)
To Soil, Soybean Yield Averages
Control
B
Mn
Zn
ns
ns
ns
55
50
45
40
Min
38
IOWA STATE UNIVERSITY
Extension and Outreach
Max
72
Avg
56
Mix Band Mix Broad
ns
ns
Foliar, Corn 2012-2014 Averages
Corn Grain Yield (bu/acre)
Control
B
Cu
Mn
Zn
ns
ns
ns
ns
Mixture
200
P <0.05
190
180
170
Min
144
IOWA STATE UNIVERSITY
Extension and Outreach
Max
255
Avg
200
To Soil, Corn Yield Averages
Corn Grain Yield (bu/acre)
200
Control
B
Mn
Zn
ns
ns
ns
190
180
170
160
Min
152
IOWA STATE UNIVERSITY
Extension and Outreach
Max
242
Avg
193
Mix Band Mix Broad
ns
ns
Soybean Grain Micros Concentration
Relative Concentration Increase
in Soybean Grain (%)
12
10
Cu
B
P <0.05
2012 sites
2013 sites
P <0.05
8
6
Mn
Zn
P <0.05
4
P <0.10
2
0
IOWA STATE UNIVERSITY
Extension and Outreach
ns
Soil and Tissue Test Methods

Soil tests
−
−
−

Dried and moist samples
Boron: hot water-CaCl2, ICP
Cu, Mn, and Zn
− DTPA, ICP
− Mehlich-3, ICP
Tissue testing
−
−
−
V5/V6; R2/R3 soybean; V8-V10 & R1 corn
Total concentration, nitric acid digestion
ICP
IOWA STATE UNIVERSITY
Extension and Outreach
DTPA vs Mehlich-3 Soil Tests
The NCERA-13 Committee recommends the DTPA test for Cu, Mn, and Zn
But several labs use the Mehlich-3 test, when there are no field calibrations
anywhere in the North-Central Region
Y = 1.68 + 1.01X
r2 = 0.31, P < 0.01
Mehlich-3 Mn (ppm)
Mehlich-3 Cu (ppm)
4.0
3.5
3.0
2.5
140
12
120
10
100
80
60
2.0
40
1.5
0.0
20
0.5
1.0
1.5
DTPA Cu (ppm)
2.0
Mehlich-3 Zn (ppm)
4.5
ns
r2 = 0.03
8
6
4
Y = 0.68 + 1.11X + 0.093X2
2
R = 0.94, P < 0.01
2
0
0
10
20
30
DTPA Mn (ppm)
40
50
0
1
2
3
4
5
6
DTPA Zn (ppm)
Consideration of pH improves
the correlation for Zn
IOWA STATE UNIVERSITY
Extension and Outreach
7
Mn by DTPA vs Mehlich-3 and Soil pH
50
140
30
20
10
0
4.5
Y = -32,4 + 16.8X
r² = 0.16, P < 0.05
100
80
60
40
5.0
5.5
6.0
6.5
Soil pH
IOWA STATE UNIVERSITY
Extension and Outreach
120
-1
-1
DTPA Mn (mg kg )
40
Mehlich-3 Mn (mg kg )
Y = 82.2 - 10.1X
r² = 0.49, P < 0.01
7.0
7.5
8.0
20
4.5
5.0
5.5
6.0
6.5
Soil pH
7.0
7.5
8.0
Did Soil and Tissue Tests Agree?
Plant at V6 vs Soil Tests
120
ns
r2 = 0.08
24
80
60
40
Y = 32.3 + 1.36X
r2 = 0.33, P < 0.01
20
0.8
1.2
1.6
0
Soil B (ppm)
Plant Zn (ppm)
Plant Cu (ppm)
20
30
40
50
15
10
ns
r2 = 0.01
1.0
1.5
Soil DTPA Cu (ppm)
IOWA STATE UNIVERSITY
Extension and Outreach
45
40
35
2.0
30
ns
r2 = 0.01
3
4
5
DTPA Cu Dry vs Cu leaf
40
0
Soil B (ppm)
35
2
50
20
10
1
60
25
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
40
0
70
30
12
25
80
30
45
20
0.5
50
Soil DTPA Mn (ppm)
20
0
0.0
10
Leaf Cu (ppm)
0.4
55
Y = 39.7 + 0.53X
r2 = 0.13, P < 0.05
90
Leaf Mn (ppm)
28
100
Leaf B (ppm)
32
Plant Mn (ppm)
Plant B (ppm)
36
5
100
ns
r2 = 0.01
60
40
20
0.0
65
6
Soil DTPA Zn (ppm)
7
20
30
40
50
Soil DTPA Mn (ppm)
45
8
6
ns
r2 = 0.01
4
2
0.0
10
50
Leaf Zn (ppm)
44
Leaves at R2/R3 vs Soil Tests
40
35
30
25
ns
r2 = 0.01
20
15
0.5
1.0
1.5
Soil DTPA Cu (ppm)
2.0
0
1
2
3
4
5
6
Soil DTPA Zn (ppm)
7
Did M3 Soil and Tissue Tests Agree?
Plant Mn (ppm)
12
10
8
6
4
1.0
2.0
2.5
100
40
80
60
40
Y = 16.2 - 2.00X
r2 = 0.26, P < 0.01
1.5
45
3.0
3.5
4.0
20
20
4.5
Soil Mehlich-3 Cu (ppm)
Leaf Mn (ppm)
8
6
4
40
60
80
100
120
140
2.5
3.0
3.5
4.0
Soil Mehlich-3 Cu (ppm)
IOWA STATE UNIVERSITY
Extension and Outreach
0
2
4
45
80
60
40
20
20
8
50
40
35
30
25
ns
r2 = 0.02
20
4.5
6
Soil Mehlich-3 Zn (ppm)
ns
r2 = 0.01
2.0
ns
r2 = 0.01
20
ns
r2 = 0.12
10
Leaf Cu (ppm)
Leaves at R2/R3
25
100
1.5
30
Soil Mehlich-3 Mn (ppm)
12
2
1.0
35
ns
r2 = 0.08
Leaf Zn (ppm)
Plant Cu (ppm)
Plants at V6
14
120
Plant Zn (ppm)
16
15
40
60
80
100
120
Soil Mehlich-3 Mn (ppm)
140
0
2
4
6
Soil Mehlich-3 Zn (ppm)
8
Why Do Soil & Tissue Tests Disagree?

One of them are wrong and useless?
− Many say soil tests aren't good
− Probably both aren't good since plant
analysis isn't that good for P, K, or S
either in corn and soybean

Perhaps soil supply was high, and there
isn't "luxury uptake" in the tissues
−
Proved luxury uptake for K but not much
for P, for example
IOWA STATE UNIVERSITY
Extension and Outreach
Plant and Leaf Tests Agreed Poorly
65
12
10
55
Leaf Cu (ppm)
Leaf B (ppm)
Y = 6.51 + 1.03X
r2 = 0.30, P < 0.01
45
35
8
6
4
25
Y = 5.46 + 0.23X
r2 = 0.15, P < 0.01
2
25
30
35
40
4
6
Plant B (ppm)
10
Leaf Zn (ppm)
60
40
40
35
30
25
Y = 9.17 + 0.63X
r2 = 0.19, P < 0.01
20
40
60
80
100
Plant Mn (ppm)
Extension and Outreach
16
45
80
IOWA STATE UNIVERSITY
14
50
Y = 30.6 + 0.33X
r2 = 0.28, P < 0.01
20
20
12
Plant Cu (ppm)
100
Leaf Mn (ppm)
8
120
20
25
30
35
Plant Zn (ppm)
40
45
Recent Results in Other States

IN, KS, MN, WI
−
−
−

Response in VERY sandy soils of IN, KS,
and MN
Response to Mn in traditionally deficient
areas of IN
Some responses to chelated Fe applied
with the seed in KS and MN
All suggest that published soil or tissue
test sufficiency ranges are too high and
encourage unneeded fertilization
IOWA STATE UNIVERSITY
Extension and Outreach
Yield Response, Soil Tests, & Expectations
Soil Testing, Single Nutrient Evaluations
80 Sites-Years with Corn and Soybean
Expectation of Yield Increase According to Interpretations
In Some States of the North-Central Region
Soil Test (ppm)
Sites with Expected Yield Increase
0.25 to 2.0
At 1 or all sites
Copper (DTPA)
≥ 0.2
At none
Manganese (DTPA)
≥ 2.0
At none
0.75 to 3.0
At 4 or 65 sites
Micronutrient
Boron (hot water)
Zinc (DTPA)
IOWA STATE UNIVERSITY
Extension and Outreach
Yield Response, Tissue Tests, & Expectations
Soybean Tissue Testing at R2/R3 Stages
56 Single Nutrient Evaluations
Expectation of Yield Increase According to Interpretations in
Some North-Central States and Published Values for the US
Micronutrient
Tissue Test (ppm)
Sites with Expected Yield Increase
Boron
21 to 55
At none or all sites
Copper
10 to 30
At 39 or all sites
Manganese
21 to 100
At none or all sites
Zinc
21 to 50
At 2 or all sites
IOWA STATE UNIVERSITY
Extension and Outreach
Published Interpretations & Expectations
Corn Tissue Testing at the Silking Stage
24 Single Nutrient Evaluations
Expectation of Yield Increase According to Interpretations in
Some North-Central States and Published Values for the US
Micronutrient
Tissue Test (ppm)
Sites with Expected Yield Increase
Boron
4 to 25
At none or all site-years
Copper
5 to 20
At none or all site-years
Manganese
15 to 150
At 1 or all site-years
Zinc
15 to 70
At 6 or all site-years
IOWA STATE UNIVERSITY
Extension and Outreach
So What Are Recent the Findings?

Typical soils of IA and the NC region
have sufficient amounts of micros

Great deal of uncertainty about the value
of soil & tissue testing and current
interpretations; most are too high

Higher removal with high yield but yield
level is not a good index of micros need

Target soils with possible deficiency
−
sandy, calcareous, organic, or severely eroded
IOWA STATE UNIVERSITY
Extension and Outreach
apmallar@iastate.edu
515-294-6200
IOWA STATE UNIVERSITY
Extension and Outreach