Plant Nutrition

All the processes that are involved in the uptake and utilization of raw materials by living organisms for their normal growth and development are called nutrition. Raw materials that are used in nutrition are called nutrients. Nutrients are inorganic substances obtained from the air (C, H2, O2) or soil. As these inorganic substances are supplied by soil in the form of minerals, hence these are mineral nutrients and the process is mineral nutrition.
Approximately 60 different minerals have been reported from plant ashes; out of 60, nearly 30 are present in all plants. Out of 30 elements, some are essential elements these are C, H, O, P, K, S, Ca, Fe, Mg, N, Na, Cu, Ni, Zn, Mn, Mo, B, Cl, and some are non-essential elements.
Every day you consume food to nourish and fuel your body, as eating many different nutrients that are essential to maintaining optimal health. These essential nutrients include vitamins, minerals, proteins, fats, and carbohydrates.
However, some nutrients are made in the human body, and these are called non-essential nutrients. Although termed non-essential, they are still required by the body for supporting daily bodily processes. Some non-essential nutrients are also found in the diet, although many are also made by the body.
About 98 percent of the mass of every living organism is composed of six elements including C, H, O, N, Ca, and P.
Essential elements in agricultural soil: * Classified into two categories: * Macro-elements (major): -These elements are required by the plant in larger quantities. These are: - C H O P K S Ca Mg N. * Micro-elements (minor): - are required by the plant in low quantities but they are also as important as macro elements. These are: - Fe Cu Ni Zn Mn B Cl Mo, etc. Fe is required in large amounts and Mo is low in comparison to other micronutrients.
The general function of mineral elements: * Framework elements: These elements are involved in the building up of cell walls and storage products of plants. E.g., C, H, O * Protoplasmic elements: These elements are components of protoplasmic constituents like nucleic acids, protein, and chlorophyll. E.g., C, H, O, N, S, P * Catalytic elements: Some elements function as part of the enzymes, without the presence of these elements some enzymes cannot function. E.g., Fe, Cu, Zn, Mg, Mn, K, etc. Mg+2 is an activator for both RuBisCo and PEPcase, both of which are critical enzymes in photosynthetic carbon fixation; Zn+2 is an activator of alcohol dehydrogenase and Mo of nitrogenase during nitrogen metabolism. * Balancing elements: These elements overcome the toxic effects of other elements. E.g., Ca, Mg, K against Mn, Zn, N, B, Cu, Pb, * Critical elements: a type of macronutrient that become commonly deficit in soil e.g., N, P, K, also called complete fertilizer, and their deficiency is called a primary deficiency. * Storage elements: C, N, S, P. (vii) Toxic elements: Al, As, Hg, Pb, Ag. (viii) Mobile elements: H, N, S, P, K, Cl, Zn, Mo, Ni. * Immobile elements: Ca, Fe, B, & Cu. (x) Non-mineral elements: - C, H, O, N. * Nitrogen is both a mineral and non-mineral element. Non-mineral nitrogen is an N2 gas in the atmosphere.
Deficiency symptoms based on the mobility of the element in the plant: * Appear first in the older tissues (Mobile elements): if elements are actively mobilized within the plants and exported to young developing tissue. E.g., N, P, K, S, Mg. * Appear first in the younger tissues (Immobile elements): if elements are relatively immobile and are not transported out of the mature organs because they are part of the structural component of the cell and hence are not easily released. E.g., Ca
Methods to study the mineral requirements of plants: * Soil normally contains sufficient quantities of essential minerals. However, three important elements need to be replenished in crop fields as they are depleted by repeated cultivation. These fertilizer elements called critical elements are N, P, and K. The common sources of these elements used in India are nitrate of sodium, ammonium sulfate, ammonium nitrate, ammonium chloride, urea, etc. The NPK fertilizers comprising bags of fertilizers are labeled 17-18-19 or 15-15-15 or other combinations. These numbers refer to the percentage by weight of nitrogen, phosphorus, and water-soluble potassium. * To determine the elements essential for plant growth and deficiency symptoms of an essential element, a well-defined nutrient medium has to be used. Seeds are grown in highly washed pure sand in a glass or glazed porcelain or plastic container and supplied with a carefully made-up nutrient solution.
Arnon and Hoagland’s Medium: They prescribed a medium containing micronutrients. Iron was earlier supplied as ferrous sulfate, but it often precipitated out. This problem has now been solved by dissolving the ferrous sulfate along with a chelating agent Na-EDTA (disodium salt of ethylene diamine tetra acetic acid).
Solution culture: It is performed in glass jars or polythene bottles. The container is covered with black paper after pouring the solution into them.

Black paper has two functions –

(a) Prevention of the growth of algae and

(b) Prevention of the reaction of roots with light.

Seeds are allowed to germinate over the split cork. Cotyledons are removed after seedling formation. The plant is properly supported with the help of split cork. The solution is aerated at regular intervals and is changed after 2-3 days.

Hydroponics: Commercial technique of soilless culture is called hydroponics, which was first developed by Julius Von Sachs in 1860, a prominent German botanist. Culture is performed in large tanks of metal or Reinforced Cement Concrete (R.C.C). Tanks are covered with wire mesh. Tanks are provided with aerating and circulating techniques. Seeds are suspended in solution from the wire mesh with the help of threads. As the plant grows up additional support is provided.
Significance: Useful in areas having thin, infertile dry soils. It can regulate the pH at optimum for a particular crop. It controls soil-borne pathogens. It avoids the problem of weeding. Out-of-season vegetables (like tomato, seedless cucumber, and lettuce) and flowers can also be obtained.
Aeroponics: It is a technique of soil-less culture in which the roots of plants are suspended amid an oxygenated nutrient solution.
SPECIFIC ROLE OF DIFFERENT ELEMENTS IN PLANTS:

Mineral elements are present in the soil either in dissolved form or in an absorbed form. Minerals are not absorbed in molecular form but absorbed in cations or anions. Absorption takes place by the cells of epiblema in the zone. Minerals are not absorbed in the zone of root hair and meristematic zones.

Carbon, Hydrogen, and oxygen: They are obtained from water and CO2 in the air. All three are components of protoplasm.
Phosphorus (P): Involve in Nucleotide (DNA and RNA) formation and cell membrane formation etc. It is an energy carrier and forms part of ATP, ADP, and NADP so involved in energy transfer reactions.

Deficiency: Poor growth, leaves dull green or with anthocyanin, chlorosis followed by necrosis. First in older leaves, poor vascular tissues, premature leaf fall, etc.

Potassium (K): Most common free Ion of the cell and also the most mobile element of the cell required for the synthesis of protein, opening, and closing of stomata, and turgor pressure of cell, also an activator of some enzymes. K involve in nerve conduction, muscle contraction in animals, etc. Deficiency: Marginal chlorosis and necrosis appear first in older leaves. Loss of apical dominance and premature death etc.
Sulfur (S): Sulphur is essential for the formation of certain vitamins like biotin, thiamine, and coenzyme A. It is essential for nodule formation in the roots of Legumes. It is found in proteins & other important substances. Deficiency: Responsible for chlorosis, first in young leaves, leaf curling, nodulation stop in Legumes, and cause of defoliation in Tea and stunted growth.
Calcium (Ca): Present in middle lamella as calcium pectate and required for division of shoot apex & root apex and also involved in cell membrane permeability. Ca is also involved in muscle activity, blood clotting, fertilization, etc. in animals and is also involved in the photolysis of water. Deficiency: Ca is important for the activity of apical meristems and mitosis so its deficiency decrease meristematic activities or stem & root tip die. Leaf with chlorosis and curling first in younger leaves and premature flower fall.
Iron (Fe): Required for ferredoxin & cytochromes formation and act as a catalyst for chlorophyll formation & used in transport in animals. Deficiency: Inter veinal chlorosis with green veins appearing first in young leaves, reduced growth.
Magnesium (Mg): Activator of enzymes of phosphate metabolism. Help in the maintenance of Ribosome and fat synthesis, and also for chlorophyll synthesis. Deficiency: Interveinal chlorosis appears first in older leaves.
Nitrogen (N2): Nitrogen is an essential constituent of proteins and protoplasm. All enzymes are proteins (except ribozyme) or their derivatives. N2 is an essential constituent of nucleic acids so helps in the synthesis of protein, chlorophyll, and cytochrome. Deficiency: -Inter veinal chlorosis with green veins appearing first in older leaves, reduced growth.
Molybdenum (Mo): -Required for nodulation in leguminous plants or activator for N2 metabolism and help in N2 fixation and for reduction of Nitrate to Nitrite and Protein synthesis also. Deficiency: -Causes mottling and marginal necrosis of leaves, called Whiptail disease.
Zinc (Zn): -Zinc is essential for the synthesis of tryptophan which is a precursor of IAA. (indol 3 acetic acid - a natural auxin) so help in auxin hormone formation. Deficiency: -Causes many diseases in plants

i. White bud in Maize.

ii. Little leaf disease, leaf rosette disease.

iii. Inter-node shorting disease.

Manganese (Mn): - Functions as an activator of several enzymes of Kreb's cycle or activator for carboxylase enzyme. Required in the photolysis of water to form O2. It is also essential for the synthesis of chlorophyll and IAA.

Deficiency: -Cause inter-veinal chlorosis with grey spots, a flower becomes sterile, called marsh spot disease.

Chlorine (Cl): -Required for ionic balance, and solute concentration, chlorine plays important role in photosynthesis especially light reaction of photosynthesis (splitting of water).

Deficiency: -Causes Bronze-colored leaves, swollen root tips, wilting & flower abscission.

Boron [B]: -Most important trace element, necessary for pollen germination, and translocation of food (sugar). It regulates cellular differentiation & development. It is essential for the formation of root nodules in the leguminous plant. Deficiency: -Causes 4 famous diseases – i. Heart rot disease of sugar beet. ii. Brown heart disease of turnip. iii. Internal cork of apple. iv. Browning of cauliflower. * Nodulation in legumes is reduced due to deficiency of ‘S’ & ‘B’.
Copper [Cu]: -Involve in plastocyanin which is used in O2 transport in many marine organisms.

Deficiency: Cause the following disease –

i. Dieback – the killing of the apical meristem.

ii. Exanthema – the killing of the apical meristem.

iii. Reclamation disease – leaf tip necrosis.

iv. Blackening of potato tuber.

Nickel [Ni+2]: it is the activator of the enzyme urease. This enzyme is required to split urea in plants' bodies to obtain nitrogen.