1. Corn and Soybean Yield Responses to Micronutrients and Relationships
with Soil and Tissue Tests
Antonio P. Mallarino
Department of Agronomy
Iowa State University

2. 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

3. 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

4. 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)
Calcareous soils pH (> 7.0)
Soybean
Manganese (Mn)
Organic soil with high pH (> 5.8),
Soybean, wheat,
oats, sugar beets
Zinc (Zn)
Sandy or organic, low organic matter due to erosion, calcareous soils
Corn, sorghum
Molybdenum (Mo)
Very acid soils (< 5.5 or so)
Legumes
Adapted from several extension publications in the North-Central region

5. Micros Removal and Yield Level in Iowa

6. Manures Supplies Micronutrients!
Manure source
Iron
Manganese
Boron
Zinc
Copper
lb/ton as-is
Dairy solid
0.5
0.06
0.01
0.03
Swine solid
19.0
1.09
0.04
0.79
0.50
Poultry
3.0
0.61
0.08
0.48
0.66
lb/1000 gal
Dairy liquid
0.9
0.11
0.12
Swine liquid
2.5
0.23
1.03
0.62
Kent Martin, Crops and Soils Specialist, KSU

7. 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

8. 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

9. Zinc Deficiency in Corn

10. 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)

11. Manganese & Glyphosate in Soybean

12. 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

13. Iron Chlorosis in Soybean

14. 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

15. 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

16. 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

17. 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)

18. 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

19. Grain Yield Response Results
56 foliar fertilization plot trials
No grain yield increase at any trial
Yield decrease at one soybean trial from Cu, Zn, and the mixture
26 foliar fertilization strip trials
One soybean yield increase
One corn yield decrease
Fertilization to soil: 8 fields, 3 years each
No yield increase or decrease at any trial
Yield levels: - Soybean bu, avg Corn 144 to 255 bu, avg 200

20. Foliar, Soybean Yield Averages
Results for three trials in 2014 are not shown
Min
Max
Avg 20 74 49

21. To Soil, Soybean Yield Averages
Min
Max
Avg 38 72 56

22. Foliar, Corn Averages
Min
Max
Avg
144
255
200

23. To Soil, Corn Yield Averages
Min
Max
Avg
152
242
193

24. Soybean Grain Micros Concentration

25. 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

26. 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
Consideration of pH improves
the correlation for Zn

27. Mn by DTPA vs Mehlich-3 and Soil pH

28. Did Soil and Tissue Tests Agree?

29. Did M3 Soil and Tissue Tests Agree?

30. 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

31. Plant and Leaf Tests Agreed Poorly

32. 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

33. 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
Micronutrient
Soil Test (ppm)
Sites with Expected Yield Increase
Boron (hot water)
0.25 to 2.0
At 1 or all sites
Copper (DTPA)
≥ 0.2
At none
Manganese (DTPA)
≥ 2.0
Zinc (DTPA)
0.75 to 3.0
At 4 or 65 sites

34. 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
Zinc
21 to 50
At 2 or all sites

35. 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
Manganese
15 to 150
At 1 or all site-years
Zinc
15 to 70
At 6 or all site-years

36. 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

37. apmallar@iastate.edu 515-294-6200