. Atoms are the smallest independent units of elements that can exist. When an atom has an electrical charge on it we call the atom an "ion". Some atoms are positively charged and called "cations", some are negatively charged and called "anions". When positive and negative ions get together in an electrically balanced marriage we call the combined result a "molecule," or if the union is electrically unbalanced it may be called a complex ion – either a complex cation or a complex anion, depending upon the nature of the final charge.
An example of a cation is Cu++ (copper); an anion is NO3- (nitrate). The two together make a copper nitrate molecule: Cu(NO3)2.
Chemical Properties of the Micronutrients
Form Used by Plant
Symbol of Form
Reaction of Hydroxide
pH 6.0 pH 8.0
Major Cause for Low Availability to Plants
Precipitates as MnO2 at high pH under well-oxidized conditions
Precipitates and is absorbed by the silicate and oxide fractions of soils
Very weak base
Precipitates as an insoluble Fe2O3.nH2O at high pH
Very weak base to acidic
Is absorbed by the silicate, oxide and insoluble organic matter fractions of soils
Very weak acid to basic
Under high rainfall soluble boron is leached and residue persists as the insoluble complex silicate tourmaline
Forms insoluble iron and aluminum molybdates in acid soils and more soluble calcium molybdates in neutral and alkaline soils
*Number 1 is most soluble. Number 6 is most insoluble.
** Any metal in a water solution passes atoms into the solution as charged ions, and these in turn tend to return to the metal state. There is a measurable electrical potential between the metal and the ion state. The negative sign on the numerical value indicates that the movement is towards the ionic state. The higher the negative number, the more active the metal is. Note that the anions are no longer pure metals but are oxides of the metal.
This table shows that each of the micronutrients has its own characteristics. When you are considering trace element fertilizers, remember the chemistry of each one individually. We make a serious mistake if we treat a copper deficiency as a manganese deficiency, or iron deficiency as a zinc deficiency. Know each micronutrient and what to expect from it.
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