Plants are autotrophic. They need inorganic substances from outside and synthesize their own organic elements. Materials needed by the plant are chiefly obtained from the soil where they are present in the form of minerals. They are called mineral nutrients. Such a nutrition is called mineral nutrition. The criteria as to which elements should be considered as essential was given by Arnon. The plant will not have normal growth without complete elements. The element is specific and cannot be replaced by another element however close it may be in the periodic table. The metabolism of the plant depends on the direct role of the element.
Categories of Essential Elements
Macro-elements : Large quantities of the elements are required by the plants. These are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, magnesium and calcium.
Micro-elements : Low quantities less than 1 ppm of micro elements are required by the plant. These are boron, zinc, manganese, iron, copper, molybdenum and chlorine.
General Functions of Mineral Elements
Framework elements of plants are carbon, hydrogen and oxygen. Nitrogen, phosphorus and sulphur are considered as protoplasmic elements as they constitute part of protoplasm. Some elements function as part of the enzyme i.e. without the presence of these elements some elements cannot function. Calcium, magnesium and potassium counteract the toxicium, magnesium and potassium counteract the toxic effect of other minerals by causing ionic balance. Dissolved mineral elements in the cell sap are found in plant cells. These elements affect the osmotic pressure of the cell.
Plant Analysis
The various mineral nutrient elements are determined even in micro and semimicro-quantities by spectro-photometric, calorimetric, flame photometric, titametric or by other methods during plant analysis. These calculations are done according to needs either in extracts of fresh plant tissue such as organic extracts or in the plants from which organic materials have been completely removed by ashing it at 500OC.
According to D.W. Rains (1976), the estimate of essential elements in higher plants is as follows—
Elements % of dry weight
Carbon 45
Oxygen 45
Hydrogen 6
Nitrogen 1.5
Potassium 1.0
Calcium 0.5
Magnesium 0.2
Phosphorus 0.2
Sulphur 0.1
Chlorine 0.01
Iron 0.01
Manganese 0.005
Boron 0.002
Zinc 0.002
Copper 0.0001
Molybdenum 0.0001
Essential Characters of Normal Nutrient Solution
1. All essential elements required by the plant must be in soluble form.
2. Solution must be dilute and should be changed frequently.
3. Solution must be balanced.
4. Solution must be aerated properly.
5. pH of solution must be in the range of 5 – 6.5.
Solution culture should be as per Knop’s formula as follows :
Ca (No3)2 – 0.8 gm/litre
MgSO4 – 0.2 gm/litre
KNO3 – 0.2 gm/litre
KH2PO4 – 0.2 gm/litre
FePO4 – Trace
The plants growing in soilless culture or solution cultures has been developed to some extent on practically large scale and is known as hydroponics.
Hydroponics
Term ‘hydroponic’ is referred to soil-less growth of plants in water and sand cultures. It was used by Gerick in 1940. The solution used in culture contains all essential elements in proper proportions for normal growth of plants. Use of hydroponics has become quite popular during recent past even for large scale commercial growth of plants such as roses, tomatoes, lettuce, carrots and potatoes.
Advantages : (i) In this method a controlled chemical composition of nutrient solution may be provided.
(ii) The growth of bacterial and higher fungi is minimised which may otherwise cause diseases of crop plants.
(iii) The culture solution is kept well aerated ensuring better environment for plant growth.
(iv) No tillering is required.
(v) In this method natural calamities such as floods, droughts, erosion etc. can be avoided.
Macronutrients
Carbon, Hydrogen and Oxygen
These are not mineral nutrients in origin but they enter into the composition of practically all organic compounds present in the plant and account for a major part of the dry weight. The significance of water (H2O) can be felt when it is said that water is elixir of life. The water and atmosphere are the main sources for oxygen and hydrogen.
Nitrogen
Deficiency symptoms—
1. Cell division and cell enlargement is inhabited.
2. If chlorophyll is less, the leaves of plant turn pale yellow. The older leaves turn completely yellow and fall because nitrogen moves rapidly from older to younger leaves.
3. In certain plants such as tomato leaf, veins turn purple or red due to development of anthrocyanin pigment.
4. Nitrogen deficiency decreases protein and starch contents.
5. Prolonged dormancy and early senescence appear.
Sulphur
Deficiency symptoms—
1. Cell division is reduced.
2. Fruit formation is retarted.
3. Leaves remain small and turn pale green, i.e., symptoms of chlorosis. Chlorosis affects young leaves more because sulphur has the non-moving property. The young leaves develop orange, red or purple pigment.
4. Leaf fall becomes fast.
5. In tobacco, tea and tomato, the leaf-tips bent downwards. The leaf margins and tips roll inwards.
6. In tea plants the tea yellow disease is caused.
7. The apical growth is inhibited whereas lateral buds develop prematurely.
8. Formation of Sclerenchyma, xylem and collenchymatous tissue gets increased.
Phosphorus
Deficiency symptoms—
1. Cambial activity is checked.
2. Tillering of crop plants is reduced.
3. The dormancy is prolonged.
4. Leaves fall in premature condition.
5. Growth of the plant is retarded and dead patches appear on leaves, petioles and fruits.
6. Variable colours develop, e.g. pale green in Pisum, olive green in Phaseolus and blue-green in Brassica sp. and cereals.
7. Thickening of tracheidial cell is reduced and phloem differentiation is found incomplete.
Calcium
Deficiency symptoms—
1. The deficiency of calcium is exhibited by the young leaves and near the grwoing point of stem and root.
2. Defficiency of calcium often causes irregular in form or often show brown scorching or spotting effects.
3. Thin chloritic marginal bands develop.
4. Severe distortion of young leaves takes place with the tips hooked back and the margins curled backward or forward.
5. Growing points are often killed in tomato.
6. In flax, cloves and many plants, petioles and pedicels also frequently collapse due to its deficiency.
Potassium
Deficiency symptoms—
1. In acute deficiency cases—
(a) Shoots may die back and finally plant may die.
(b) Plants may become stunted with numerous tillers.
(c) Flowering may not be there or little flowering may take place.
2. In mild deficiency—
1. Thin shoots may develop.
2. Shoot growth may be restricted.
3. Mild deficiency gives the leaf a dull or bluish green.
4. Chlorosis occurs in interveinal regions.
5. In older leaves, browning of tips (tip burns), marginal scorching (leaf scorch), or development of brown spots near the margins takes place.
6. Scorched margins of leaves often turn forward or upward.
7. Reduced internodes of stem and of grains result.
8. The lamina of broad leaved plants curl backward towards the under surface or roll forwards towards the upper surface parallel with the midrib.
Magnesium
Deficiency symptoms—
1. Magnesium deficiency is exhibited on the older leaves and proceed systematically towards the younger leaves.
2. Chlorosis takes place.
3. Severely affected leaves may wither and shed or absciss without the withering stage. Defoliation may by early and severe.
4. Magnesium deficiency causes necrotic spots on leaves.
Micro-Nutrients Iron
Deficiency symptoms—
1. Chlorosis of leaves occurs and young leaves are always most severely affected. Principal veins may remain green.
2. Chlorosis may produce a mottled pattern or leaf may show complete bleaching.
3. Iron deficiency may cause scorching of leaf margins and tips.
Manganese
Deficiency symptoms—
1. Manganese deficiency is exhibited by chlorosis of leaves.
2. Over the leaf scattered dead tissue spots are found.
3. In older leaves.
4. In oats, development of gray-speck disease due to manganese deficiency causes total failure of the crops.
5. Severely affected tissues turn brown, the brown areas may also twist in the form of spirals and they may wither also.
6. The root system is poorly developed and badly affected, plants may die.
7. Grain formation is also reduced and the heads may be blind.
Copper
Deficiency symptoms—
1. Copper deficiency makes both vegetative and reproductive growth reduced.
2. The foliage may, however show burning of the margins or chlorosis or rosetting, multiple bud formation may occur, gumming may also occur.
3. In crops, the younger leaves wither and show yellowing-grey of the tips in several crops. The disease is known as yellow tip or reclamation disease.
4. Heads are dwarfed, distorted and tips tend to be chlorotic.
5. Grain formation is badly restricted than vegetative growth.
Zinc
Deficiency symptoms—
1. Zinc deficiency symptoms in Citrus are widespread where mottle leaf gets developed.
2. It also causes other diseases such as little leaf or rosette of apples, vines, stone fruits and walnut yellows.
3. Zinc deficiency also results in the bronzing of twigs and white tips of maize.
4. Zinc deficiency symptoms in broad-leave crops are interveinal chlorosis often with necrosis and pigmentation, leaf size is reduced, scarcity of foliage and shortening of internodes etc.
5. A close relationship between zinc and chlorophyll formation is found.
Molydenum
Deficiency symptoms—
1. In tomato, chlorosis appears in the form of mottling in the older leaves.
2. Deficiency symptoms develop from younger leaves in certain cases.
3. In acute deficiency of molybde-num, necrosis of leaf tissue occurs.
4. In oats, grain formation does not take place.
5. Moly response have also been reported to form whip tail in cauliflower and brassica.
Boron
Deficiency symptoms—
1. Several diseases are born because of Boron deficiency. These are Heart rot of sugar beet and marigold, Canker of table beet, browning and hollow stem of cauliflower, cracked stem of alfalfa, Hard fruits of Citrus, top sickness of tobacco and water core in turnip.
2. Leaves show appearance of white stripe, scorching, pimpling, splitted midrib, reduced growth and distortion like cupping and curling.
3. Deficiency symptoms are shown by stem like die-back of apex, abnormal tillering, appearance of various forms of deformities such as curling and brittle lesions pimpling etc.
4. Lesser number of sterile flowers are produced.
5. Deformed and useless fruits are produced.
Chlorine
Chlorine is obtained in soil as chlorides and moves freely in soil solution from which it is available to plants. No general statement can be made regarding the role of chlorine in plant metabolism. In tobacco it has been shown to increase the water content of cells and to affect carbohydrate metabolism. Recent studies show that though present in plants in quite large quantities, chlorine is the seventh essential trace element for plants.
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