Explain with examples: macronutrients, micronutrients, beneficial nutrients, toxic elements and essential elements.

Explanation

(i) Macronutrients. They are generally present in plant tissues in large amounts (in excess of 10 m mole `Kg^(-1)` of dry matter) e.g. phosphorus, sulphur, potassium, calcium and magnesium.
(ii) Micronutrients. They are trace elements which are needed in very small quantity (less than 10 m mole `Kg^(-1)` of dry matter) e.g. iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel.
(iii) Beneficial nutrients. Beneficial elements (nutrients) are those nutrients which are useful to plants in small or large quantities. However, they are additional to 17 essential elements. Examples of beneficial elements are sodium, silicon, cobalt and selenium.
(iv) Toxic elements. Any mineral ion concentration in tissues that reduces the dry weight of tissues by about 10 per cent is considered toxic. The requirements of micronutrients is in small quantity but their moderate decrease leads to formation of deficiency symptoms and a moderate increase show toxic effects. Excess of manganese induces deficiencies of iron, magnesium and calcium. Any mineral ion that reduces the dry weight of tissues by about 10% is called a toxic element.
(v) Essential elements. Such elements are absolutely necessary for supporting normal growth and reproduction. Such elements are specific and are not replaceable by another element. Essential elements are directly involved in the metabolism of plant. Examples of essential elements are calcium, hydrogen, oxygen, etc.