1. Micronutrient elements
General Characteristics

2. Micronutrients in Soils and Crops
Soil Content (kg/ha)
Corn Removal (kg/ha)
Boron (B)
22-225
0.07
Copper (Cu)
2-450
0.06
Iron (Fe)
11,200 – 224,000
0.12
Manganese (Mn)
112-11,200
0.09
Molybdenum (Mo)
1-8
0.03
Zinc (Zn)
22-675
0.17

3. Forms taken up by plants
Micro nutrient
Forms in soil solution
Iron
Fe2+, Fe(OH)+, Fe(OH)2+, Fe3+
Manganese
Mn2+
Zinc
Zn Zn(OH)+
Copper
Cu Cu(OH)+
Molybdenum
MoO42- HMoO4-
Boron
H3BO3 , H2BO3-
Cobalt
Co2+
Chlorine
Cl-
nickel
Ni2+, Ni2+
Specific forms present are determined by pH and soil aeration
Under acidic conditions simple cation forms dominate
Hydroxyforms –dominant under alkaline codns
Under acid conds MoO42- reacts like phosphorus
in alkaline soils B exists as anion

4. General Characteristics
A.  Micronutrients are required by all plants but in smaller amounts compared to the macronutrients.
Deficiencies of micronutrients can reduce growth just as much as deficiencies of macronutrients. Remember the “Law of the Minimum”.

5. General Characteristics
B The amount of micronutrient that is needed by the plant can have a narrow range. If the amount of micronutrient is too high, it is possible for toxicity to occur.
Available forms
1.  Cations: Fe2+, Fe3+, Mn2+, Zn2+, Cu2+
2.  Anions: MoO42-, Cl-
3.  Neutral: H3BO3

6. Micronutrient function in plants
1.  Enzymes and coenzymes
a)   Structural component of enzymes
b)   Involved in the activation and regulation of enzymes
2.  Oxidation and reduction reactions
Micronutrients are involved in electron transport

7. Transformations in the soil
The transformations that micronutrients undergo in the soil vary depending on the nutrient, but overall, the reactions are similar to what has already been discussed for macronutrients.
a)  Mineralization and immobilization
b)  Adsorption and desorption to clay or organic matter surfaces
c) Precipitation and dissolution of secondary minerals

8. Transformations in the soil
-chelation process
One transformation is quite different from transformations associated with macronutrients-- chelation.
The word chelate means “claw”. Chelation refers to the process in which organic molecules in the soil form a complex with micronutrient ions.
  The chelated micronutrients are carried by mass flow and diffusion to the root surface.

9. The chelation process in the soil
The chelate is broken down in rhizosphere . The micronutrient is taken up by the root and the organic molecule diffuses away.
The organic molecule can complex with more micronutrients and the process is repeated.

10. The chelation process in the soil
a lot about the chelation of micronutrients is still unknown. The organic molecule that forms the chelate may be derived from:
Natural chelates
(1)  Organic compounds released by the plant roots (phytosiderophores) or soil microorganism, (Siderophores)
(2)  Compounds released during the decomposition of soil organic matter, such as fulvic acids
(3) Man-made chelates: EDTA, DTPA EDDHA etc

11. The chelation process in the soil
Soluble chelates increase the availability of micronutrient cations: Fe, Zn, Mn, and Cu. The chelates help protect the ions from precipitation or adsorption reactions.

12. Factors that affect micronutrient availability
  Solubility of the micronutrient (affected by factors such as pH)
  Percent of exchange sites that are occupied by the micronutrient)
 Soil organic matter
(1)  Affects the balance between adsorption and desorption
(2) Organic matter is also involved in the chelation process