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There are 17 known essential elements required by plants, of which 14 are known as mineral nutrients because they are normally extracted from the soil, while the other three (carbon, hydogen and oxygen) are acquired from photosynthesis. Some elements such as sodium, silicon and cobalt, may be essential for some plant species but not others.
They are often grouped into categories that reflect the relative amounts of each element found in plant tissue (it does not suggest that plants tend to become deficient in one group more than others).

Primary Nutrients: nitrogen (N), phosphorous (P), potassium (K). Plants require these elements in large amounts and deficiencies are usually corrected by traditional fertilisers.

Macronutrients: calcium (Ca), magnesium (Mg), sulphur (S).

Micronutrients (also called trace elements): boron (B), copper (Cu), iron (Fe), chlorine (Cl), manganese (Mn), molybdenum (Mo), zinc (Zn), nickel (Ni).

Modern Plant Nutrition offer chelates of five mineral nutrients that are commonly deficient in Australian agriculture: calcium, magnesium, zinc, iron and manganese. A brief description of the role of these nutrients in plant physiology is given below.

Calcium is critical for the physical integrity of cell walls and for the process of cell division and is an important factor in regulating the activities of a number of growth enzymes. Although soil usually has abundant calcium, deficiency can often occur because the calcium ion (Ca++) has low mobility in plants: symptoms of deficiency therefore typically first appear in young, rapidly growing tissues such as new leaves and fruit (calcium chelated with amino acids, however, is mobile and transported through the plant via the phloem).

Magnesium is critical for leaf health and most magnesium in a plant resides in chlorophyll (magnesium is a building block of chlorophyll). Magnesium also plays essential roles in activating growth enzymes, energy reactions (ATP: adenosine triphosphate - a high-energy cellular fuel) and photosynthetic carbon fixation. Magnesium is mobile in plants so deficiency usually appears as chlorosis of the older leaves. Plants grown in acidic, sandy soils are at higher risk for magnesium deficiency.

Zinc is an activator of a very large number of enzymatic reactions in plants and therefore has a very wide range of effect. Its most visible activity may be the metabolism of the auxin plant growth hormone indole-3-acetic acid (IAA). Although the precise role of zinc in auxin metabolism is not well understood, zinc deficient plants show growth abnormalities such as shortened internodes (the sections of stem between leaf nodes) and "little leaf" disorder. Zinc has a relatively high mobility within plants and deficiency is likely due to low soil availability. The solubility (and hence availability) of zinc in soil is strongly affected by pH, with solubility decreasing with increasing pH (i.e. alkaline soils). Various soil types are particularly at risk for zinc deficiency: calcareous, sodic, volcanic ash, scraped, sandy and any soil that is continuously wet, regardless of pH.

Iron acts as a catalyst in many redox (reduction-oxidation) reactions in photosynthesis and respiration and is required for the synthesis of chlorophyll. Iron deficient plants display interveinal chlorosis. Because the mobility of iron in plants is very low, chlorosis usually appears in the youngest leaves first (iron chelated with amino acids, however, is mobile and translocated throughout the plant via the phloem). Iron deficiency is common because it is very susceptible to forming insoluble hydrous oxides that cannot be used by plants; especially in alkaline soils with a pH greater than 6.5.

Manganese is involved in a number of enzymatic reactions in plants, however it is best known for its role in photosynthetic oxygen production. Manganese deficiency can be widespread in some areas depending on soil conditions: especially those with high pH (alkaline) and high organic matter content. The cereal grains are especially susceptible to developing manganese deficiency. Manganese has a relatively low mobility within plants and early symptoms may be an interveinal chlorosis of the younger leaves appearing quite similar to iron deficiency (which is often present simultaneously). Manganese chelated with amino acids has high mobility within plants and is transported via the phloem.