What are the essential elements for plants? Give the criteria of essentiality. How are minerals classified depending upon the amount in which they are needed by the plants?
Any element that fulfills the essentiality criteria is called an essential element for plants. Some of the various criteria for the essentiality of an element are –
(a) The element must be particularly important for facilitating normal growth and reproduction of the plant.
(b) The requirement of the element must be specific, and it should not be replaceable by any other element.
(c) Direct involvement of the element in metabolism in the plant should be present. Minerals are divided into two categories, viz. macronutrients and micronutrients based on the amount in which minerals are needed.
Macronutrients: Elements that are present in large amounts, that is >10 m mole per kg of dry matter, are macronutrients. Examples include carbon, oxygen, hydrogen, nitrogen, etc.
Micronutrients: Elements that are present in small amounts, that is < 10 m mole per kg of dry matter, are micronutrients. Examples include iron, calcium, magnesium, etc.