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After reading this article you will learn about the essential and non-essential elements of plants.
Criteria of Essentiality of an Element:
Arnon and Stout (1939) proposed three criteria for the essentiality of an element:
(a) In the absence of an element, it is not possible for plant to complete its vegetative or reproductive cycle (life cycle).
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(b) The role played by an element is specific and it cannot be replaced by any other element.
The acute deficiency of the element produces certain well-defined symptoms of disease which are not produced by the deficiency of any other element. Deficiency disease can be cured by the supply of the particular element.
(c) The element is directly involved in nutrition of the plant. The search for essential elements has required the development of a technique for growing the plant in the absence of impurities. This meant the elimination of natural root medium in the soil. In its place, a pure sand or water or solution culture has been used.
Essential Elements for Plants:
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Plants contain small amounts of 90 or more elements, only 16 of which are known to be essential to plants. These elements are: Carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, iron, sulpur, boron, manganese, copper, zinc, molybdenum and chlorine.
Non-Essential and Useful Elements:
Plants contain small amounts of 90 or more elements, only 16 of which are known to be essential to plants. Although plants absorb a large number of elements, all of them are not essential for the growth of crops. The elements are absorbed because they happen to be in the soil solution.
It has been found that the presence of some elements which are not considered essential for plant growth and are not directly concerned in the nutrition of the crop, but are present in the plants used as food and feed, are of vital importance to the health of man and animals. The elements within this group are iodine, cobalt and sodium.
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Some elements, occurring freely in the soil, are absorbed by the plants as impurifiers. They may occasionally stimulate growth although they are not essential for plant growth. They include lithium, strontium, tin, radium, beryllium, vanadium, mercury, silver and bromine.
Stiles (1961) reports the essentiality of vanadium, sodium, silicon, aluminium, and gallium for certain species of plants.
Usefulness of Vanadium:
Vanadium is found very useful for algae. It helps in the growth of algae. This element is involved in photosynthesis. Although there is no evidence for the indispensability of vanadium for plants other than green algae, this element is widely distributed in the plant kingdom.
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Usefulness of Silicon:
Silicon is a major constituent of the soil and is present in many plant species. Silicon releases fixed phosphorus from deficient soils, and promotes the growth of all kinds of crop plants. Silicon increases the resistance of gramineae, especially rice, against some diseases and insects. Silicon enhances the development of rice crop from heading to ripening.
Usefulness of Strontium:
Tensho (1959) reported the absorption of strontium by rich plants. Strontium is similar to calcium in chemical behaviour. The accumulation of strontium in the rice grain is also reported by scientists.
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Usefulness of Cobalt:
It helps in the fixation of nitrogen by bacteria. Cobalt increases the photosynthesis and growth of the plant. It activates many enzymes.
Usefulness of Sodium:
It gives resistance against drought especially in sugar beet. Sodium affects water absorption and metabolism in the plant.
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