Plants need not less than sixteen different nutrients from the soil in order to fully develop. Six of these nutrients are most essential. Six macronutrients, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) are absolutely essential plant nutrients.
The three main nutrients are nitrogen (N), phosphorus (P), and potassium (K). Together they make up the trio known as NPK. Other important nutrients are calcium, magnesium, and sulfur. Plants also need small quantities of iron, manganese, zinc, copper, boron, and molybdenum, known as trace elements because only traces are needed by the plant.
Nitrogen (N)
Nitrogen is a key element in plant growth. It is found in all plant cells, in plant proteins and hormones, and in chlorophyll.
Atmospheric nitrogen is a source of soil nitrogen. Some plants such as legumes fix atmospheric nitrogen in their roots; otherwise, fertilizer factories use nitrogen from the air to make ammonium sulfate, ammonium nitrate, and urea. When applied to soil, nitrogen is converted to mineral form, nitrate, so that plants can take it up.
Soils high in organic matter such as chocolate soils are generally higher in nitrogen than podzolic soils. Nitrate is easily leached out of the soil by heavy rain, resulting in soil acidification. You need to apply nitrogen in small amounts often so that plants use all of it, or inorganic form such as composted manure, so that leaching is reduced.
Phosphorus (P)
Phosphorus helps transfer energy from sunlight to plants, stimulates early root and plant growth, and hastens maturity.
Very few Australian soils have enough phosphorus for sustained crop and pasture production and the North Coast is no exception. The most common phosphorus source on the North Coast is superphosphate, made from rock phosphate and sulfuric acid. All manures contain phosphorus; manure from grain-fed animals is a particularly rich source.
Potassium (K)
Potassium increases the vigor and disease resistance of plants, helps form and move starches, sugars, and oils in plants, and can improve fruit quality.
Potassium is low or deficient on many of the sandier soils of the North Coast. Also, heavy potassium removal can occur on soils used for intensive grazing and intensive horticultural crops (such as bananas and custard apples).
Muriate of potash and sulfate of potash are the most common sources of potassium.
Calcium (Ca)
Calcium is essential for root health, the growth of new roots and root hairs, and the development of leaves. It is generally in short supply in the North Coast's acid soils. Lime, gypsum, dolomite, and superphosphate (a mixture of calcium phosphate and calcium sulfate) all supply calcium. Lime is the cheapest and most suitable option for the North Coast; dolomite is useful for magnesium and calcium deficiencies, but if used over a long period will unbalance the calcium/magnesium ratio. Superphosphate is useful where calcium and phosphorus are needed.
Magnesium (Mg)
Magnesium is a key component of chlorophyll, the green coloring material of plants, and is vital for photosynthesis (the conversion of the sun's energy to food for the plant). Deficiencies occur mainly on sandy acid soils in high rainfall areas, especially if used for intensive horticulture or dairying. Heavy applications of potassium in fertilizers can also produce magnesium deficiency, so banana growers need to watch magnesium levels because bananas are big potassium users.
Magnesium deficiency can be overcome with dolomite (a mixed magnesium-calcium carbonate), magnesite (magnesium oxide), or Epsom salts (magnesium sulfate).
Sulfur (S)
Sulfur is a constituent of amino acids in plant proteins and is involved in energy-producing processes in plants. It is responsible for many flavors and odor compounds in plants such as the aroma of onions and cabbage.
Sulfur deficiency is not a problem in soils high in organic matter, but it leaches easily. Superphosphate, gypsum, elemental sulfur, and sulfate of ammonia are the main fertilizer sources.
Trace Elements
Iron (Fe)
Iron is a constituent of many compounds that regulate and promote growth.
Manganese (Mn)
Manganese helps with photosynthesis.
Copper (Cu)
Overuse of another trace element, molybdenum, can cause a copper deficiency in animals. Toxicity can be a problem for horticulturists who regularly use Bordeaux mixture or copper oxychloride sprays to control diseases on horticultural crops.
Zinc (Zn)
Zinc helps in the production of a plant hormone responsible for stem elongation and leaf expansion. Easily cured with the addition of zinc sulfate or crushed zinc minerals. Fruit trees can be sprayed with zinc.
Boron (B)
Boron helps with the formation of cell walls in rapidly growing tissue. Deficiency reduces the uptake of calcium and inhibits the plant's ability to use it. Easily remedied with borax applied to the soil.
Molybdenum (Mo)
Molybdenum helps bacteria and soil organisms convert nitrogen in the air to soluble nitrogen compounds in the soil, so is particularly needed by legumes. It is also essential in the formation of proteins from soluble nitrogen compounds.
Can be remedied easily with applications of Mo super, molybdenum trioxide (applied during inoculation and lime pelleting of legume seed), or sodium molybdate (sprayed on young emerging plants).