Category : 11th Class
Ash analysis : The plant tissue is subjected to a very high temperature (550-600°C) in an electric muffle furnace and is reduced to ash. The plant ash left behind forms a very small proportion of plants dry weight ranging from 2 to 10% only. Analysis of plant ash shows that about 92 mineral elements are present in different plants. Out of these, 30 elements are present in each and every plants and rest are in one or other plants. Out of these 30 elements, 16 elements are necessary for plants and are called essential elements.
Solution culture (Hydroponics) : In this method plants are grown in nutrient solutions containing only desired elements. To determine the essentiality of an element for a particular plant, it is grown in a nutrient medium that lacks or is deficient in this element.
The growing of plants with their roots in dilute solutions of mineral salts instead of soil led to increased understanding of plant nutrition. This cultivation of plants by placing the roots in nutrient solution is called hydroponics. Probably the first recorded use of soilless culture was by Woodward in 1699. By 1860, the culture solution technique was modernized by Sachs and he showed the essentiality of nitrogen for plant growth.
Another significant worker for studying the essentiality of elements was Knop (1865). The method of growing plants in aqueous nutrient solutions as employed by Sachs and Knop is used experimentally and commercially today and known as hydroponic culture. Now a days a chelating agent Na2-EDTA (Disodium salt of ethylene diamine tetra acetic acid. EDTA (Ethylene diamine tetra-acetic acid) is a buffer which is used in tissue cultures) is added.
Hydroponics or soilless culture helps in knowing
(1) The essentiality of mineral element.
(2) The deficiency symptoms developed due to non-availability of particular nutrient.
(3) Toxicity to plant when element is present in excess.
(4) Possible interaction among different elements present in plant.
(5) The role of essential element in the metabolism of plant.
Solid medium culture : In this method either sand or crushed quartz is used as a rooting medium and nutrient solution is added to it. The nutrient medium is provided by one of the following methods :
Drip culture : It is done by dripping over the surface.
Slop culture : It is done by having the medium over the surface.
Sub-irrigation : Here the solution is forced up from the bottom of the container.
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