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FERTILIZER BASICS
By Gary King, Ph.D. , Corky’s Pest Control
There are 16 chemical elements necessary for plants. Three of these, carbon from carbon dioxide in
the air, hydrogen from water, and oxygen from air, are used in large amounts for the building blocks
of life. The roots in the soil normally take up the other thirteen elements that are needed. These are
grouped as primary nutrients, secondary nutrients, and micronutrients. Plants use these nutrients
to make the cellulose, protein, enzymes and other components of the leaves, roots, flowers, stems, fruit,
etc.; to run numerous metabolic systems; and to capture the sun’s energy to make sugars during photo-
synthesis.
The nutrients are supplied in many forms, some organic (e.g., decaying organic plant and animal materi-
als; chicken, horse and cow manures; fishmeal; blood meal) and some manufactured products, such as
liquids, soluble powders, and granulars.
Primary Nutrients
A common granular fertilizer label is shown on the opposite page. As with all modern fertilizers, the
label tells the amounts of the 3 primary nutrients, AKA macronutrients or major nutrients, which are
nitrogen (N), phosphorus (P), and potassium (K). These numbers are the percent by weight of each in
the mix, in this case represented by the numbers, “16-6-8.” The higher the number, the more concen-
trated the nutrient. The balance of the 3 nutrients (referred to as the NPK ratio), their chemical formula-
tion, and the concentration of them are designed for specific purposes.
In a grossly over-simplified rule, products with high nitrogen, relative to P and K, generally produce
more lush leaf growth. Products with higher phosphorus, relative to N and K will generally stimulate
flower blooms. Materials containing higher potassium, relative to the other two, will encourage plant
hardiness in thicker leaves, better rooting, and disease resistance.
The chemical formulations of the NPK will make them more or less rapidly useable to the plants. Plants
most rapidly assimilate nitrogen when it is in the nitrate form, so most quick-acting fertilizers for use in
cold weather will have a calcium nitrate or ammonium nitrate formulation. Next in order of rapidly used
forms is the ammonical form, such as ammonium sulfate, ammonium phosphate, or ammonium nitrate.
Even slower releasing forms of nitrogen are urea, urea formaldehyde, and isobutylidene-diurea (IBDU),
which are useful for prolonged feeding of plants.
Phosphorus can be formulated in a number of common forms, such as finely ground rock phosphate,
phosphoric acid, ammonium phosphate, and triple super phosphate.
Potassium can be supplied in fertilizers as potassium chloride, potassium sulfate, potassium nitrate,
and sulfate of potash- magnesia. Nitrate and sulfate forms are preferred over the chloride form in areas
where chloride build-up in the soil is a problem.
Secondary Nutrients
Calcium, sulfur, and magnesium are considered secondary nutrients. Calcium is supplied by calcium
nitrate in some fertilizer formulations, manure, soil amendments (gypsum, dolomite, hydrated lime, etc.),
and even irrigation water. Calcium supplements may be unnecessary for most growing situations, but
especially beneficial for fruiting plants such as tomato.
Sulfur is beneficial in acidifying the soil, increasing iron availability and uptake, and increasing the
hardiness of plants. It is often supplied as sulfates of nitrogen, gypsum, elemental sulfur, iron sulfates,
manure, river and rainwater, and some pesticides.
Magnesium can be supplied by magnesium sulfate (Epsom salts), commonly used for palms, or as po-
tassium-magnesium sulfate and magnesium nitrate, which may be used on citrus.
Micronutrients
Iron, copper, manganese, zinc, boron, molybdenum are micronutrients that are available as inorganic
salts, chelates, and natural organic complexes. Chelated and organic complexes make the micronutri-
ents more soluble for uptake from the soil and are the easiest for plants to use.
Coated Fertilizers
In addition to using the more prolonged release forms of nitrogen, special coating can encapsulate
fertilizer prills to release the nutrients in a more controlled time frame. Some of these coatings may be
sulfur, resin, or polymers. Temperature, moisture, microbial degradation, weathering, or a combination
of these factors may affect the release of nutrients from these specialty fertilizers.
68
FERTILIZER BASICS
By Gary King, Ph.D. , Corky’s Pest Control
There are 16 chemical elements necessary for plants. Three of these, carbon from carbon dioxide in
the air, hydrogen from water, and oxygen from air, are used in large amounts for the building blocks
of life. The roots in the soil normally take up the other thirteen elements that are needed. These are
grouped as primary nutrients, secondary nutrients, and micronutrients. Plants use these nutrients
to make the cellulose, protein, enzymes and other components of the leaves, roots, flowers, stems, fruit,
etc.; to run numerous metabolic systems; and to capture the sun’s energy to make sugars during photo-
synthesis.
The nutrients are supplied in many forms, some organic (e.g., decaying organic plant and animal materi-
als; chicken, horse and cow manures; fishmeal; blood meal) and some manufactured products, such as
liquids, soluble powders, and granulars.
Primary Nutrients
A common granular fertilizer label is shown on the opposite page. As with all modern fertilizers, the
label tells the amounts of the 3 primary nutrients, AKA macronutrients or major nutrients, which are
nitrogen (N), phosphorus (P), and potassium (K). These numbers are the percent by weight of each in
the mix, in this case represented by the numbers, “16-6-8.” The higher the number, the more concen-
trated the nutrient. The balance of the 3 nutrients (referred to as the NPK ratio), their chemical formula-
tion, and the concentration of them are designed for specific purposes.
In a grossly over-simplified rule, products with high nitrogen, relative to P and K, generally produce
more lush leaf growth. Products with higher phosphorus, relative to N and K will generally stimulate
flower blooms. Materials containing higher potassium, relative to the other two, will encourage plant
hardiness in thicker leaves, better rooting, and disease resistance.
The chemical formulations of the NPK will make them more or less rapidly useable to the plants. Plants
most rapidly assimilate nitrogen when it is in the nitrate form, so most quick-acting fertilizers for use in
cold weather will have a calcium nitrate or ammonium nitrate formulation. Next in order of rapidly used
forms is the ammonical form, such as ammonium sulfate, ammonium phosphate, or ammonium nitrate.
Even slower releasing forms of nitrogen are urea, urea formaldehyde, and isobutylidene-diurea (IBDU),
which are useful for prolonged feeding of plants.
Phosphorus can be formulated in a number of common forms, such as finely ground rock phosphate,
phosphoric acid, ammonium phosphate, and triple super phosphate.
Potassium can be supplied in fertilizers as potassium chloride, potassium sulfate, potassium nitrate,
and sulfate of potash- magnesia. Nitrate and sulfate forms are preferred over the chloride form in areas
where chloride build-up in the soil is a problem.
Secondary Nutrients
Calcium, sulfur, and magnesium are considered secondary nutrients. Calcium is supplied by calcium
nitrate in some fertilizer formulations, manure, soil amendments (gypsum, dolomite, hydrated lime, etc.),
and even irrigation water. Calcium supplements may be unnecessary for most growing situations, but
especially beneficial for fruiting plants such as tomato.
Sulfur is beneficial in acidifying the soil, increasing iron availability and uptake, and increasing the
hardiness of plants. It is often supplied as sulfates of nitrogen, gypsum, elemental sulfur, iron sulfates,
manure, river and rainwater, and some pesticides.
Magnesium can be supplied by magnesium sulfate (Epsom salts), commonly used for palms, or as po-
tassium-magnesium sulfate and magnesium nitrate, which may be used on citrus.
Micronutrients
Iron, copper, manganese, zinc, boron, molybdenum are micronutrients that are available as inorganic
salts, chelates, and natural organic complexes. Chelated and organic complexes make the micronutri-
ents more soluble for uptake from the soil and are the easiest for plants to use.
Coated Fertilizers
In addition to using the more prolonged release forms of nitrogen, special coating can encapsulate
fertilizer prills to release the nutrients in a more controlled time frame. Some of these coatings may be
sulfur, resin, or polymers. Temperature, moisture, microbial degradation, weathering, or a combination
of these factors may affect the release of nutrients from these specialty fertilizers.
60