Mineral nutrition of plants was a phenomenon known from very ancient times. Woodward (1699) observed for the first time that plants grow better in muddy water than rain water. Later it was proved that minerals have specific functions in plant metabolism.
When an oven-dried plant material is ignited at 400-600 o C, all the organic materials are oxidized and incombustible matter remains as plant ash. When this ash was analysed it was found to contain 40 elements besides C,H,O,N and S which were oxidized. All these are not essential for plant nutrition but on analysis the important essential elements have been identified and based on their role in plant metabolism and requirement, they have been classified as major elements and trace elements.
The functions of the various minerals in general depends on the role of the mineral in plant metabolism.
Essential elements should have the following characteristics
i. Normal growth and reproduction must be dependent on particular mineral elements.
ii. An essential element must have direct influence on the plant.
iii. Essential elements must be indispensable and their substitution by other elements must be impossible.
iv. Some elements are required in very low quantities and the status of essentiality or non essentiality is doubtful. For examplesilicon.
i) Mineral elements are constituents of the various parts of plant body, for example calcium which is found in the middle lamella, nitrogen and sulphur in proteins, phosphorus in nucleic acids.
ii) The mineral elements influence the osmotic pressure of the plant cell.
iii) The mineral elements absorbed from the soil affect the pH of the cell sap.
iv) Elements like Fe, Cu, Mn and Zn act as catalysts in various enzymatic processes.
v) Elements like Ca, Mg, Na and K or their salts neutralize the toxic effects of other elements in the cell.
vi) Elements like As, Cu, and Hg show toxic effects at certain stages of the plant.
Deposition of ions like K+ and Ca++ on cell membrane change its permeability.
The term hydroponics has been used for growth of plants in water culture. This may also be referred to as soil-less agriculture, test-tube farming, tank farming or chemical gardening.
Commercially hydroponic cultures are maintained in large shallow concrete, cement wood or metal tanks in which gravel and nutrient solutions are taken. The tanks are provided with pumps and empty auxiliary tanks to pump out and circulate the growth solution and to maintain proper aeration of the nutrient solution.
The technique of hydroponics is employed to know which mineral element is essential for the growth and development of the plant. Commercially the application of hydroponics involve the production of horticultural and floricultural crops. This method may be used to increase yield of ornamentals such as gladioli, snapdragon, roses and vegetables such as carrot, radish, potatoes, tomatoes and lettuce.
i. It is possible to provide the desired nutrient environment.
ii. The acid-base balance can be easily maintained.
iii. Mulching, changing of soil and weeding are eliminated.
iv. Proper aeration of nutrient solution is possible.
v. Labour for watering of plants can be avoided.
vi. Tilling is not necessary.
i. Production is limited when compared to field conditions.
ii. Technical skill is required to design equipment.
iii. If a disease appears all plants in the container will be affected.
Can be used only for short duration.