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Secondary Nutrients

Essential plant nutrients, chemical symbols and sources

Mostly from Air and Water (non-mineral)   From Soil and/or Fertilizers (Mineral)  
Element Symbol Element Symbol
Carbon C Nitrogen N
Hydrogen H Phosphorus P
Oxygen O Potassium K
    Calcium Ca
    Magnesium Mg
    Sulfur S
    Iron Fe
    Mangeanese Mn
    Zinc Zn
    Copper Cu
    Boron B
    Molybdenum Mo
    Chlorine Cl


The essential plant nutrients may be grouped into three categories.

They are as follows:

  1. Primary nutrients - nitrogen, phosphorus and potassium
  2.  Secondary nutrients - calcium, magnesium and sulfur
  3. Micronutrients - iron, manganese, zinc, copper, boron, molybdenum, and chlorine


Secondary Elements  
Calcium (Ca) Calcium fertilizers are not usually needed in Oklahoma. Common sources of supplemental Ca are lime and gypsum.
Calcium Carbonate (Lime) 20-40% Ca
Calcium Sulfate (Gypsum) 23% Ca, (18.6% Sulfur)
Normal Superphosphate  22% Ca, (20% P2O5, 12% Sulfur)
Magnesium (Mg) The most common sources of magnesium are magnesium sulfate and dolomitic lime.
Magnesium Oxide  52% Mg
Magnesium Sulfate 16% Mg
Potassium - Magnesium Sulfate (Sul-Po-Mag, K-Mag) 11% Mg, (22% K2O, 22% Sulfur)
Dolomitic Limestone (varies) 12% Mg
Sulfur (S) Sulfur is most available when supplied in the highly water soluble sulfate form.  Ag. sulfur (elemental sulfur) can be used, but requires biological oxidation over time to convert the elemental form to available sulfate.
Calcium Sulfate (Gypsum) 17% S (22% Ca)
Potassium Sulfate 17% S
Sulfate of Potash, Magnesia 22% S
Ammonium Sulfate 24% S
Normal Superphosphate 12% S
Ammonium Thiosulfate 26% S
Boron (B) A sodium borate (solubor) containing about 20% B is the source of B most commonly used in liquids.  Boric acid and other soluble forms containing between 14 to 20% B are also suitable for liquid mixes.
Borax  11.3% B

Exerts from Oklahoma Soil Fertlity Handbook 2006 (Zhang and Raun 2006).



Zinc (Zn), Iron (Fe), Copper (Cu), and Manganese (Mn):

The micronutrient elements can be discussed as a group since their sources are somewhat similar.  Industry separates the compounds into two general categories; inorganic and organic.  Inorganic include sulfates, oxides, carbonates and chlorides.  The term organic applies primarily to chelated products and some sequestered materials.  Most chelates, and particularly liquid products, can be mixed with liquid without difficulty.


  Zinc Sulfate 25-36% Zn
  Zinc Oxide  50-80% Zn
  Zinc Chloride 48% Zn
  Zinc Chelate 9-14.5% Zn
  Ferrous Sulfate 20.1% Fe
  Ferric Sulfate 19.9% Fe
  Ferrous Ammonium Sulfate 14.2% Fe
  Ferric Chloride 34.4% Fe
  Iron Chelate 10% Fe
  Copper Sulfate  25% Cu
  Manganese Sulfate 23-28% Mn
Molybdenum (Mo) Ammonium molybdate is satisfactory for liquids.  Sodium molybdate can also be used although it is less soluble than ammonium molybdate.  Since Mo is applied in ounces per acre, liquids are ideal for getting even distribution.  
  Sodium Molybdate 39.7% Mo
  Ammonium Molybdate 54.3% Mo
Chlorine Chlorine has only recently been found deficient in Oklahoma soils.  The deficiency in wheat on deep sandy soils near Perkins, OK can be corrected using muriate of potash (0-0-60).  This is the common source of potassium, which is usually also deficient in these sandy soils.  

Exerts from Oklahoma Soil Fertlity Handbook 2006, (Zhang and Raun 2006).


A table describing the symptoms shown in a plant correlated with the nutrient it is deficient in.

Table 4.11 from Oklahoma Soil Fertility Handbook 2006, (Zhang and Raun 2006).

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