Plant nutrition is the study of the uptake, transport, and function of nutrients in plants. Plant nutrients are known also as essential elements. These are chemical elements that are required for plant growth. They must be supplied whether the system is organic or otherwise. For a chemical element to be considered as a plant nutrient, several criteria must be met:
(1) The element must be required for plants to complete their life cycles. Each element has a direct effect on plant growth or metabolism. Deficiency of an essential element will result in abnormal growth or premature death of plants.
(2) The requirement for these elements is universal among plants; that is, all plants, not just a few, require these elements. If some plants require an element and others do not, the element is not considered to be a nutrient but a beneficial element.
(3) No other element will substitute fully for an essential element. Partial substitution might occur among some elements, but each plant nutrient has a role for which no other element can substitute.
Today, 17 chemical elements are recognized as essential for plants. Of these elements, three—carbon, hydrogen, and oxygen—are obtained from the air. Fourteen are derived from the soil. The requirement for each essential element is absolute, regardless of the source or amount required. Hence no nutrient is more important than another one, because each one is required absolutely for plant growth and metabolism. As differences in amounts of requirements, elements are divided into classes of macronutrients and micronutrients . On a dry weight basis, the concentrations of macronutrients in plants range from about 0.3% to 5% or higher, depending on the plant part and species under consideration.