The elements that are essential for plant nutrition are:
1. Carbon, Hydrogen and Oxygen : They are obtained from water and CO2 of air. All the three are components of protoplasm and most of the other organic compounds found in the plant.
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2. Nitrogen : Chief source of nitrogen are the nitrates of Calcium and Potassium. In low concentrations ammonical form of nitrogen can also be absorbed. Certain bacteria or certain higher plants with the help of bacteria are capable of taking atmospheric nitrogen.
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Nitrogen is essential constituent of proteins and protoplasm. All enzymes are proteins or their derivatives. It is an essential constituent of nucleic acids. Nitrogen starvation causes poor root development and lowering of respiration rate. Chlorophyll is not formed in the plant (Chlorosis). Flowering and fruiting is greatly reduced.
3. Sulphur : Sulphur is absorbed as sulphate. It is component of protoplasm and favours root formation. If there is deficiency of sulphur, chlorophyll formation is hindered, there is retardation of cell division, supressing of fruit formation. Sulphur is essential for the formation of certain vitamins like biotin, thiamine and coenzyme A. It is essential for nodule formation in roots and is part of ferredoxin.
4. Phosphorus :Absorbed as phosphate. It is more abundant in growing and storage organs. It is essential constituent of DNA and RNA and nucleoproteins. It is an energy carrier and forms part of ATP, ADP and NADP. It favours healthy root growth by helping translocation of foods. Phosphorus also promotes fruit ripening and also helps in respiration. Phosphorus deficiency hinders cambial activity and inhibits the reduction of nitrates so that protein synthesis is retarded. Its deficiency promotes leaf fall and delays flowering.
5. Calcium : It is obtained from the soil in the form of its nitrate and sulphate. It is rich in older tissues and is part of middle lamella (Calcium pectate) which is a cementing material between different cells. Calcium stimulates development of root hairs. Its deficiency leads to reduced activity of chlorophyll, so it is more important for green plants. Its deficiency retards movements of carbohydrates and amino acids. It also controls cell permeability and activity of some enzymes. It is important for activity of apical meristems and mitosis.