Why (iron) chelates…
…and which one?
Bob Greensmith
Solufeed Ltd
Top Quality Speciality Fertilizers
Fe chelates? March 16
1
Plant nutrients
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Fe chelates? March 16
2
Iron chemistry
Fe3+ + e-
Fe2+
Ferric
Ferrous
Iron III
Iron II
Oxidation
Reduction
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Fe chelates? March 16
3
Iron biochemistry
• Chlorophyll production!
• Enzyme systems
• Peroxidase
• Cytochrome b
• Cytochrome c
• Catalase
• Cytochrome f
• Nitrate reductase
Auxin metabolism
Respiration
Respiration
H2O2 breakdown
Photosynthesis
Nitrogen metabolism
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Fe chelates? March 16
4
Iron deficiency symptoms
Cucumber
Orange
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Fe chelates? March 16
5
Iron deficiency symptoms
Blueberry
Strawberry
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Fe chelates? March 16
6
Iron biochemistry
Relative enzyme activity
[Fe] µg/g
[Chlorpl]
mg/g
Catalase
Peroxidase
10.3
4.53
100
100
4.3
0.25
20
56
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Fe chelates? March 16
7
Iron forms
Minerals
5–8%
Precipitates
Iron
Organics
Fe3+
1µM or
0.056 ppm
Ions
Fe2+
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Fe chelates? March 16
8
Iron chemistry
Fe(OH)3 + 3H+
Fe3+ + 3H2O
Precipitated
Ionic
Oxidation
Reduction
Alkaline
Acid
Log [Fe3+]
7
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pH
Fe chelates? March 16
9
-
Bicarbonate ions (HCO3 )
1. Present in poor quality water.
2. Naturally produced in calcareous soils:
Ca2+
CaCO3 + CO2 + H2O
+ 2HCO3
-
3. Generated by plants:
NO3
-
HCO3
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-
Fe chelates? March 16
10
-
Bicarbonate ions (HCO3 )
❖ Affect the iron uptake process by plant roots.
❖ Interfere with iron translocation from root to
leaf.
❖ Increase iron deficiency and problems.
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Fe chelates? March 16
11
Iron uptake (dicots)
Soil
Fe3+
Chelate
Fe3+
R
Fe2+
-e
H+
Xylem
Citrate
ATP
_
Fe3+
Fe3+
ROOT HAIR
Antagonists
-
OH
HCO3
Cold temperature
Anaerobic conditions
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Fe chelates? March 16
12
Iron sources (fertilizers)
•Inorganics
•Complexes
•Chelates
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Fe chelates? March 16
13
Iron sources - inorganic
Fe2(SO4)3
2Fe3+ + 3SO42-
Fe3+ + 3OH-
Fe(OH)3
“Fe+” + “PO4-“
“Fe
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P
”
Fe chelates? March 16
14
Iron sources - complexes
Eg. amino acid complex (glycine)
Open to attack
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Fe chelates? March 16
15
Iron sources – synthetic chelates
EDTA
Fe3+
O
O
N
Fe
N
= FeEDTAO
O
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Fe chelates? March 16
16
Iron sources – synthetic chelates
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DTPA
Fe chelates? March 16
17
Iron sources – synthetic chelates
o-o EDDHA 6 positions are occupied
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EDDHA
o-p EDDHA 5 positions are occupied
Fe chelates? March 16
18
Synthetic chelates properties – pH stability
EDDHA
100
EDTA
% Total
Fe Chelated
DTPA
50
HEDTA
Amino Acids
But not quite so
simple.....
Citrates
0
4
5
6
7
8
9
10
pH
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Fe chelates? March 16
19
Synthetic chelates properties – pH stability
In soft and hard water
Chelate
Soft water 1⁰
Hard water 20⁰
FeEDTA
7.3
6.7
FeDTPA
8.0
7.4
FeEDDHA
>10
>10
Source: Akzo Technica leaflet 412
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Fe chelates? March 16
20
Synthetic chelates properties – pH stability
In the final nutrient solution
Chelate
Only Fe chelated
All metals chelated
FeEDTA
6.3
7.1
FeDTPA
6.8
7.8
FeEDDHA
>10
>10
Source: Akzo Technica leaflet 412
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Fe chelates? March 16
21
Synthetic chelates - properties
N
K
Ca
Mg
S
Cu
Mn
Zn
Fe
B
Mo
Na
Cl
P
HCO3
H+
OH-
CuEDTAMnEDTAZnEDTA-
FeEDTA
Fe3+
“FePO4”
pH
Fe(OH)3
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Fe chelates? March 16
22
Synthetic chelates properties – pH stability
Stability Constant = log K = n
[MC]
K     10n
[M ][C ]
Chelating agent
Stability constant
Theoretical MAX
operating pH
EDDHA
33.91
8.8
DTPA
28.60
7.9
EDTA
25.10
7.3
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Fe chelates? March 16
23
Summary
Chelate
Variants
FeEDTA
Ammonium, potassium
and sodium salts.
Solids and liquid
FeDTPA
Sodium, hydrogen and
ammonium salts.
Liquids and solids
FeEDDH(x)A
Many homologues,
grades and qualities
Solid and liquid
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Key points
pH < 6.0 – 6.5
Acid soils only
Well controlled hydroponics
Foliar application
pH < 7.0 – 7.5
Moderate soils
Hydroponics and fertigation
pH 4.0 - > 8.0
Unaffected by bicarbonate
Soil application
Special hydroponics applications
Fe chelates? March 16
24
All available from Solufeed
Salt
Fe Analysis
(% w/w)
Formulation
K
6.0
Microgranues
Solufeed Fe 7.7EDTA-L
NH4
7.7
Liquid
Solufeed Fe 13 EDTA
Na
13.2
Crystalline powder
pH!
Solufeed Fe 3.0 DTPA-L
Na
3.0
Liquid
Econ
6.0
Liquid
Na free
Product Name
KaliFer (FeKEDTA)
Solufeed Fe 6.0 DTPA-L
NH4
Key points
pH!
Na free
pH!
Na free
Solufeed Fe 7.0 DTPA
Na
7.0
Microgranules
Economical
Solufeed Fe 11 DTPA
H
11.0
Microgranules
Na free Premium
Solufeed Fe 7.0 EDDHA Regular
Na
7.0
Microgranules
Economy grade
Solufeed Fe 6.0 EDDHA Extra
Na
6.0
Microgranules
3.8 % o-o
Solufeed Fe 6.0 EDDHA Premium
Na
6.0
Microgranules
4.8 % o-o
Solufeed Rapid
Na
2.0
Liquid
High performance
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Fe chelates? March 16
25
Thank you
Any questions?
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Fe chelates? March 16
26
Some maths!
In an ordinary soil.......
Assuming 10-6 M Fe3+ is necessary,
and Fe3+ is very insoluble
Ie. [Fe3+][OH-]3 = 10-36
Then [10-6] [OH-]3 = 10-36
Using FeEDTA instead.......
[Fe3+][EDTA4-]
= 10-26
[FeEDTA-]
Let [Fe3+] and hence [FeEDTA-] = 10-6
So, [Fe3+][EDTA4-]
= 10-26
[10-6]
and [OH-]3 = 10-30
Therefore, [Fe3+][EDTA4-]
and [OH-] = 10-10
Or [Fe3+] = [EDTA4-]
= 10-32
= 10-16
But pH = log [H+]
But, [Fe3+][OH-]3 = 10-36
and [H+][OH-] = 10-14
Then [OH-]3 = 10-30
And [OH-] = 10-6.67
Therefore [H+] = 10-4
So [H+] = 10-7.33
Ie. pH = 4 !!
Ie. pH = 7.33
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Fe chelates? March 16
31
Iron chemistry
Log [Fe3+]
7
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pH
Fe chelates? March 16
32