Plants need both, inorganic as well as organic matter, for their nutrition. This is called mineral nutrition. They get inorganic matter from outside and organic matter they synthesize for themselves.
If the elements needed by a plant are not received by it, it can not complete its life cycle. Elements help in the metabolic activity of the plant.
Essential Elements
Plants need Macro and micro elements. Macro elements, which are required in large quantities, are—
(a) carbon (b) hydrogen
(c) oxygen (d) nitrogen
(e) phosphorus (f) potassium
(g) magnesium and (h) calcium.
Elements needed in small quantities are called micro elements. These are boron, zinc, manganese, iron, copper, molybdenum and chlorine.
Functions of Mineral Elements
The framework of a plant is done by carbon, hydrogen and oxygen. The elements used in protoplasm are nitrogen, phosphorus and sulphur. Calcium, magnesium, and potassium are enzyme elements. Calcium, magnesium, and potassium counteract the toxic effects. Some elements influence the osmotic pressure. Percentage of different elements in the plants is as follows—
Characters of Nutrient Solution—
(a) Nutrient elements must be in solution form.
(b) Solution should be dilute.
(c) Solution must be balanced.
(d) pH should be in the range 5-6.5.
Hydrophonics : Hydrophonics is the cultivation of plants by placing the roots in nutrient solution.
Macronutrients
Carbon : Carbon is considered as the building block of organic compounds.
Hydrogen : Hydrogen is contained in water and organic compounds. These substances are used by plants. In aerobic respiration atomic oxygen combines with hydrogen to form metabolic water.
Oxygen : Oxygen is used in aerobic respiration. Water is a significant substance useful for plant life. Atmosphere and water are the main sources for carbon, oxygen and hydrogen.
Nitrogen : It is the main constituent of amino acids, proteins, nucleic acids, enzymes, vitamins, ATP and chlorophyll.
Nitrogen is fixed for plants by certain bacteria.
If there exists a nitrogen deficiency, its symptoms are that the protein and starch contents are decreased, chlorophyll gets reduced, and there is prolonged dormancy, etc.
Sulphur : It is used by plant as soluble sulphates in the soil. Sulphur is a constituent of certain amino acids, proteins, vitamins, etc. Sulphur gives odour in onion, garlic, etc. Sulphur increases nodule formation.
Its deficiency symptoms are—
(a) Cell division is reduced.
(b) Its deficiency reduces fruit formation.
(c) Leaves remain small and their colour becomes pale green.
(d) Leaves fall fast.
(e) Tea plants suffer with tea yellow disease.
(f) The leaves of tobacco, tea and tomato bend downward.
Phosphorus : Plants take phosphorus as soluble phosphates.
Phosphorus is the main constituent of cell membrane, nucleic acids, ADP, ATP etc.
Its deficiency symptoms are—
(a) Tillering of crop plants is reduced.
(b) Dormancy prolonged.
(c) Leaf fall is prematured.
(d) Variable colours develop.
Calcium : Calcium carbonate is used as the main source of calcium. Other minerals are also there which provide calcium. CO2 also increases the solubility of carbonates in the soil.
It is found in leaves. It is the chief constituent of cell wall. It is an activator of ATP. It counter acts metal toxicity.
Calcium deficiency often appears as brown scorching. Thin chlorotic marginal bands develop. In tomato growing points are often killed.
Potassium : It goes into the plants as potash felspar, mica, gluconite in soluble form.
It is an important metabolite for proteins, fats and carbohydrates. It is found in all parts of the plant.
The plant dies due to its deficiency. No flowering takes place due to potassium deficiency. The colour of leaves becomes dull bluish green.
Magnesium : Magnesium is used as carbonates in soil in the dissolved form.
It is a constituent of chlorophyll. It is essential for synthesis of fats.
Due to its deficiency leaves may wither. Necrotic spots develop on leaves. Chlorosis occurs.
Micronutrients
Iron : Needed for chlorophyll synthesis.
It is a constituent of ferredoxin, cytochromes and flavoproteins. Acts as catalyst and activator of nitrate reductase and acronitase.
Manganese : Activates some enzymes and plays a structural role in chloroplast membrane system.
Zinc : Required for auxin synthesis and activates various enzymes especially carboxylases, part of carbonic anhydrase and various dehydrogenases.
Copper : Activates certain enzymes and acts as a constituent of plastocyanin.
Molybdenum : An important constituent of nitrate reductase system and plays a role in symbiotic nitrogen fixation.
Boron : Required for uptake and utilisation of Ca2+, carbohydrate translocation, pollen germination; regulates cell differentiation and development; enhances RNA synthesis and plays a role in nitrogen metabolism.
Chlorine : Essential for photolysis of water and oxygen evolution in photosynthesis and in maintaining ionic balance in cells.
Deficiency Symptoms of Mineral Nutrients
Iron : Interveinal white chlorosis in young leaves and inhibits chloroplast formation and protein synthesis.
Manganese : Deficiency causes Chlorotic or necrotic spots in interveinal areas; grey spots on leaves; root system poorly developed.
Zinc : Interveinal chlorosis of old leaves followed by white necrotic spots; distortion of leaves; reduction in fruits and seeds; formation of smaller leaves and shortened internodes.
Copper : Die back of shoots; necrosis of tip and margins of young leaves; reclamation disease in cereals and leguminous crops.
Molybdenum : Slight retardation of growth; inhibits flower formation and if at all formed they abscise before setting of fruits; mottling and marginal wilting of leaves.
Boron : Brown disease; hypertrophy followed by death of shoot tips; leaves become brittle; roots turn short and stubby; early fall of flower and fruits.
Chlorine : Affects photosyn-thesis, roots become short, thick and club shaped near the tip; appearance of wilted leaves.
Passive absorption : Absorption of ions (mineral salts) which does not involve participation of metabolic energy, is called passive absorption. Molecules or ions diffuse from a region of their high concentration to a region of their lower concentration.
Donann equilibrium theory : Entry of ions into the cell across the plasma membrane to maintain electrical equilibrium is called Donann equilibrium.
Active absorption : It is defined as the uptake of mineral ions against concentration gradient achieved by an input of energy. The energy required is derived from respiration and is supplied through ATP.
