List of sixteen essential plant nutrients:- 1. Nitrogen 2. Phosphorus 3. Potassium 4. Calcium 5. Magnesium 6. Sulphur 7. Iron 8. Manganese 9. Copper 10. Zinc 11. Boron 12. Molybdenum 13. Silicon 14. Sodium 15. Vanadium 16. Cobalt.
Plant Nutrient # 1. Nitrogen:
Nitrogen is a vitally important plant nutrient. Plant normally contains 1-5% by weight of this nutrient.
The important functions of it are as follows:
(i) Nitrogen is an essential constituent of proteins and is present in many other compounds of great physiological importance in plant metabolism e.g. nucleotides, phosphatides, alkaloids, enzymes, hormones, vitamins, etc. It is, therefore, a basic constituent of “life.”
(ii) Nitrogen is an integral part of chlorophyll, which is the primary absorber of light energy needed for photosynthesis. The basic unit of chlorophyll’s structure is the porphyrin ring system, composed of four pyrrole rings, each containing one nitrogen and four carbon atoms. A single magnesium atom is bonded in the centre of each porphyrin ring.
(iii) Nitrogen also imparts vigorous vegetative growth dark green colour to plants.
(iv) It produces early growth and also results delay in maturity of plants.
(v) It governs the utilization of potassium, phosphorus and other elements.
(vi) The supply of nitrogen is related to carbohydrate utilization. When nitrogen supplies are insufficient, carbohydrates will be deposited in vegetative cells, which will cause them to thicken. When nitrogen supplies are optimum and conditions are favourable for growth, proteins are formed from the manufactured carbohydrates.
Less carbohydrate is thus deposited in the vegetative portion, more protoplasm is formed, and, because protoplasm is highly hydrated, a more succulent plant results. Excessive supply of nitrogen develops excessive succulence which results harmful effects in some crops like weakening of fibre in case of cotton, lodging in case of grain crops etc.
(vii) Nucleoproteinsâ€”a complex group of proteins is involved in the control of developmental and hereditary processes. One of these proteins, deoxyribonucleic acid (DNA) is present in the nucleus and the mitochondria of the cell. During meristematic growth DNA duplicates all the genetic information that the cell possesses and passes this information via chromosomes to each daughter cell.
Plant Nutrient # 2. Phosphorus:
(i) Phosphorus has a great role in energy storage and transfer.
(ii) Phosphorus is a constituent of nucleic acid, phytin and phospho-lipids. An adequate supply of phosphorus early in plant life is important for the reproductive parts of the plants.
(iii) It is also an essential constituent of majority of enzymes which are of great importance in the transformation of energy, in carbohydrate metabolism, in fat metabolism and also in respiration of plants.
(iv) It is closely related to cell division and development.
(v) Phosphate compounds act as “energy currency” within plants. The most common phosphorus energy currency is that found in adenosine di and triphosphate (ADP and ATP). Donation or transfer of the energy-rich phosphate molecules from ATP to energy-requiring substances in the plant is known as phosphorylation.
In this reaction ATP is converted back to ADP or ADP back to adenylic acid, with a phosphate molecule being left attached to the phosphorylated compound. The compounds ADP and ATP are formed and regenerated in the presence of sufficient phosphorus at sites of energy production.
(vi) It stimulates early root development and growth and there by helps to establish seedlings quickly.
(vii) It gives rapid and vigorous start to plants, strengthens straw and decreases lodging tendency.
(viii) It brings about early maturity of crops, particularly the cereals, and counteracts the effects of excessive nitrogen.
(ix) Large quantities of phosphorus are found in seed and fruit and it is considered essential for seed formation. Phytin composed of calcium and magnesium salts of phytic acid, is the principal storage form of phosphorus in seeds.
(x) The supply of phosphorus improves the quality of certain fruit, forage, vegetable, and grain crops and increases the disease resistance of crops.
(xi) It enhances the activity of rhizobia and increases the formation of root nodules and thereby helps in fixing more of atmospheric nitrogen in root nodules.
(xii) Excess of phosphorus may cause deficiency of certain micro-nutrients especially zinc and iron. On the other hand, phosphorus alleviates the detrimental effects of over-liming.
Plant Nutrient # 3. Potassium:
(i) Potassium exists in mobile ionic (K+) form and its function appears to be primarily catalytic in nature.
(ii) Enzyme activationâ€”Over 60 enzymes have been identified that require potassium for their activation. These enzymes are involved in so many important plant physiological processes that enzyme activation is regarded as potassium’s single most important function.
(iii) Water relationsâ€”The pre-dominance of potassium over other cations, in plants makes its role in osmotic regulation particularly important. Potassium provides much of the osmotic “pull” that draws water into plant roots. Plants that are deficient in potassium are less able to withstand water stress, mostly because of their inability to make full use of available water.
(iv) The deficiency of potassium imparts the malfunctioning of stomata which are related to lower rates of photosynthesis and less efficient use of water. So potassium can affect the rate of transpiration and water uptake through regulation of stomatal opening.
(v) The potassium has some roles in energy relations. Plants require potassium for the production of high-energy phosphate molecules (ATP), which are produced due to photosynthesis and respiration. The deficient of potassium leads to the decreased assimilation of sugars from carbon-dioxide during photosynthesis.
(vi) It imparts winter hardiness to legumes and other crops.
(vii) It counteracts the harmful effects to excess nitrogen in plants.
(viii) Translocation of assimilatesâ€”The translocation of assimilated sugars from leaves is greatly reduced in potassium deficient plants.
(ix) Potassium helps in formation of proteins and chlorophyll.
(x) Potassium is required for the activation of starch synthetase enzyme which controls the rate of incorporation of glucose into long-chain starch molecules. Conversion of soluble sugars into starch is a vital step in the grain-filling process.
(xi) Potassium is reported to have a beneficial effect on symbiotic N2 fixation by leguminous plants. High potassium supply has increased nodule mass, N2 fixation rate, nitrogenase activity and plant growth.
(xii) Potassium enhances carbohydrate assimilate transport to nodules and utilization for the synthesis of amino acids.
(xiii) Potassium produces strong stiff straw in cereals and thereby reduces lodging in cereals.
(xiv) Potassium imparts increased vigour and disease resistance to plants.
(xv) Potassium deficiencies greatly reduce quality and crop yields. Serious yield reductions may occur without the appearance of deficiency symptoms. This phenomenon is known as “hidden hunger” and this phenomenon occurs not only for potassium but also for other nutrient elements.
Plant Nutrient # 4. Calcium:
(i) Calcium is another secondary nutrient element required by all higher plants absorbed as Ca2+ ions.
(ii) Calcium is a constituent of the cell wall and it increases stiffness of plants.
(iii) Calcium has an essential role in cell elongation and division.
(iv) Calcium accumulates during respiration by mitochondria and it increases their protein content.
(v) It promotes early root development and growth of plants.
(vi) A deficiency of calcium manifests itself in the failure of terminal buds of plants to develop. So it is essential to activate growing, especially root tips.
(vii) Calcium influences the water-economy of the plant, protein-carbohydrates ratio in fat metabolism as well as many other physiological processes.
(viii) It improves the uptake of other plant nutrients like nitrogen and other micro-nutrients viz. iron, boron, zinc, copper and manganese.
(ix) Calcium plays an important role in the structure and permeability of cell membranes. Calcium enhances uptake of nitrate-nitrogen and therefore is interrelated with nitrogen metabolism.
(x) Calcium has a specific function in the organization of chromatin or of the mitotic spindle. It is directly involved in chromosome stability and that it is a constituent of chromosome structure. It also affects the translocation of carbohydrate in plants.
(xi) Calcium is generally considered to be an immobile element and so it cannot move freely from the older to younger parts of plants and that is why calcium deficiency symptoms are manifested at the tips of shoots and roots.
(xii) Calcium encourages seed production.
Plant Nutrient # 5. Magnesium:
(i) Magnesium is a constituent of chlorophyll, because chlorophyll formation usually accounts for about 15 to 20 per cent of the total magnesium content of plants.
(ii) It imparts dark green colour in leaves.
(iii) Magnesium also serves as a structural component in ribosomes. It appears to stabilize the ribosomal particles in the configuration necessary for protein synthesis.
(iv) Magnesium also activates the formation of polypeptide chains from amino acids.
(v) Magnesium is a mobile element and is readily trans-located from older to younger plant parts during its deficiency.
(vi) Magnesium also plays an important role for the formation of carbohydrates, fats and vitamins etc.
(vii) Magnesium is involved in a number of physiological and biochemical functions. It is associated with transfer reactions involving phosphate-reactive groups. Magnesium is required for maximal activity of almost every phosphorylating enzyme in carbohydrate metabolism. Magnesium forms a chelated structure with the phosphate groups which allow maximal activity in the transfer reactions.
(viii) Magnesium acts as a cofactor for certain enzymes other than those involved in phosphate transfer. It has a vital role in the activation of enzyme RuDP carboxylase which is found in chloroplast. Magnesium increases the affinity of the enzyme for carbon dioxide.
(ix) Magnesium brings about significant increases in the oil content of several crops.
(x) Magnesium regulates the uptake of other nutrients and the base economy of plants.
Plant Nutrient # 6. Sulphur:
(i) Sulphur is required for the synthesis of the sulphur-containing amino acids cystine, cysteine and methionine. One of the main functions of sulphur in proteins or polypeptides is the formation of disulphide bonds between polypeptide chains. Disulphide linkages are important in stabilizing and determining the configuration of proteins.
(ii) Sulphur is needed for the synthesis of other metabolites, including coenzyme A, biotin, thiamin or vitamin B1 and glutathione.
(iii) It is a component of other sulphur-containing substances, including S-adenosyl methionine, formylmethionine, lipoic acid and sulpho-lipid.
(iv) It is a vital part of ferredoxins, a type of non-heme iron sulphur protein occurring in the chloroplasts which is important for the light and dark reactions of photosynthesis.
(v) Although not a constituent, sulphur is required for the synthesis of chlorophyll.
(vi) It occurs in volatile compounds responsible for the characteristic taste and smell of plants in the mustard and onion families.
(vii) Sulphur activates a number of proteolytic enzymes such as the papainases.
(viii) It increases root growth.
(ix) Sulphur stimulates seed formation.
(x) Sulphur promotes nodule formation on roots of leguminous plants.
Plant Nutrient # 7. Iron:
Iron helps in the formation of chlorophyll. A deficiency of iron causes chlorosis between the veins of leaves and the deficiency symptom show first in the young leaves of plants. It does not appear to be trans-located from older tissues to the tip meristem and as a result growth ceases.
(ii) Iron helps in absorption of other nutrient elements.
(iii) Iron is a structural component of porphyrin molecules like cytochromes, hemes, hematin, ferrichrome and leghemoglobin. These substances are involved in oxidation-reduction in respiration and photosynthesis.
(iv) Iron is also a structural component of nonheame molecules like ferredoxins (stable Fe-S proteins). Ferredoxin is the first stable redox compound of the photosynthetic electron transport chain.
(v) Iron is a constituent of enzyme systems and so it helps for carrying out different enzymatic reactions in plants like, cytochrome oxidase, catalase, peroxidase, acotinase, nitrogenase etc.
Plant Nutrient # 8. Manganese:
(i) The role of manganese is regarded as being closely associated with that of iron. Manganese also supports the movement of iron in the plant.
(ii) Manganese helps in chlorophyll formation.
(iii) Manganese also takes part in oxidation-reduction processes and decarboxylation and hydrolysis reactions.
(iv) Manganese is needed for maximal activity of many enzyme reactions in the citric acid cycle.
(v) Manganese influences auxin levels in plants and high concentrations of Mn favour the breakdown of indole acetic acid (1AA).
(vi) It takes part in electron transport in photosystem II.
(vii) Manganese has some roles for the maintenance of chloroplast membrane structure.
(viii) It also takes part in enzyme systems like, chromatin-bound RNA polymerase, synthesis of tRNA-primed oligoadenylate, inactivation of indole acetic acid protectors, NAD malic enzyme of aspartate type C4 plants.
(ix) An optimum manganese supply sometimes helps in counteracting the bad effect of poor aeration.
(x) Manganese deficiency also shows interveinal chlorosis of plants.
Plant Nutrient # 9. Copper:
(i) Copper forms various compounds with amino acids and proteins in the plant.
(ii) Copper helps in the utilization of iron during chlorophyll synthesis. Lack of copper causes iron to accumulate in the nodes of plants.
(iii) Copper has some indirect effects on nodule formation.
(vi) Copper has an unique involvement in enzyme systems of plants like, oxidase enzymes, terminal oxidation by cytochrome oxidase, photosynthetic electron transport mediated by plastocyanin etc.
(v) It also acts as “electron carrier” in enzymes which bring about oxidation-reduction reactions in plants.
Plant Nutrient # 10. Zinc:
The role of zinc in plant nutrition is given below:
(i) Zinc influences the formation of some growth hormones in the plant.
(ii) Zinc is helpful in reproduction of certain plants.
(iii) It is associated with water uptake and water relations in the plant.
(iv) It is involved in auxin metabolism like, tryptophan synthetase, tryptamine metabolism.
(v) Zinc also influences the activity of dehydrogenase enzymes e.g. pyridine nucleotide, glucose-6 phosphate and triose phosphate etc.
(vi) The other roles attributed to zinc include phosphodiesterase, carbonic anhydrase, synthesis of cytochrome c etc.
(vii) Zinc also stabilizes ribosomal fractions.
Plant Nutrient # 11. Boron:
(i) The primary role of boron is associated with the calcium metabolism.
(ii) Boron increases the solubility of calcium as well as mobility of calcium in the plant.
(iii) It acts as a regulator of K/Ca ratio in the plant.
(iv) It helps in the absorption of nitrogen.
(v) Boron is concerned with precipitating excess cations, buffer action, regulatory effect on other nutrient elements etc.
(vi) Boron is required for the development of new cells in meristematic tissue.
(vii) Boron is necessary for proper pollination and fruit or seed setting.
(viii) It is necessary for the translocation of sugars, starches, phosphorus etc.
(ix) Boron is required for the synthesis of amino acids and proteins.
(x) It helps for the formation of nodules in leguminous plants.
(xi) Boron regulates carbohydrate metabolism.
Plant Nutrient # 12. Molybdenum:
(i) Molybdenum is an essential component of the major enzyme nitrate reductase in plants.
(ii) The molybdenum requirement of plants is influenced by the form of inorganic nitrogen supplied to plants, with either nitrate (NO3–) or ammonium (NH4+) effectively lowering its need.
(iii) Molybdenum is also a structural component of nitrogenase, the enzyme actively involved in nitrogen fixation by root-nodule bacteria of leguminous crops, by some algae and actinomycetes, and by free-living-nitrogen fixing organisms such as Azotobacter.
(iv) Molybdenum is also reported to have an essential role in iron absorption and translocation in plants.
Plant Nutrient # 13. Silicon:
Silicon is one of the most abundant elements in the lithosphere and is present in many plant species. Silicon seems to be essential for plants such as rice, sugarcane etc.
Soluble silica exists mainly as monosilicic acid [Si(OH)4], and plants are believed to absorb it in this form from the soil solution. Silicon apparently contributes to the structure of cell walls. This silica primarily impregnates the walls of epidermal and vascular tissues, where it appears to strengthen the tissues, reduce water loss, and inhibit fungal infection.
The beneficial effects of silicon have been attributed to correction of soil toxicities arising from high levels of available Mn, Fe2+ and active aluminium. Silicon also provides greater stalk strength and resistance to lodging, increased availability of phosphorus, reduced transpiration etc. Silicon tends to maintain erectness of rice leaves, increases photosynthesis because of better light interception.
The oxidising power of rice roots and accompanying tolerance to high levels of iron and manganese were found to be very dependent on silicon nutrition. Supplemental silicon was beneficial when the silica concentration in rice straw fell below 11 per cent.
Plant Nutrient # 14. Sodium:
This element is essential for halophytic plant species which accumulate sufficient of its salts in vacuoles to maintain turgor and growth. Many plants that possess the C4 dicarboxylic photosynthetic pathway require sodium as an essential nutrient. Sodium helps in oxalic acid accumulation in plants and also influences potassium sparing action. It has some roles in stomatal opening and it can regulate the activity of nitrate reductase.
Plant Nutrient # 15. Vanadium:
Low concentrations of vanadium are beneficial for the growth of microorganisms, animals and higher plants. Vanadium may partially substitute for Mo in fixation of atmospheric nitrogen by micro-organisms such as the rhizobia. It plays a role in biological oxidation-reduction reactions.
Plant Nutrient # 16. Cobalt:
Cobalt is essential for micro-organisms fixing atmospheric nitrogen. Cobalt forms vitamin B12 during growth and development of symbiotic micro-organisms like ihizobia, cyanobacteria etc.
Cobalt forms a complex with nitrogen atoms in a porphyrin ring structure which provides a prosthetic group for association with a nucleotide in the B12 coenzyme. ‘This cobalt- complex is termed the cobamide coenzyme.
Cobalt also takes part in leghemoglobin metabolism and ribonucleotide reductase in rhizobium. It also influences the growth of the plant, transpiration, photosynthesis etc.