Crop nutrition
In nature there are 109 elements and out of these only 17 elements are essential. Arnon and Stout (1939) first proposed the term criteria of essential and later Arnon (1954) revised some of the criteria and concluded the three essential criteria.
Criteria of essentiality of nutrients:
- A mineral element is considered essential to plant growth and development if the element is directly involved in plant metabolic function. Ex. N involved in protein synthesis, K involved in stomata opening and closing and sugar translocation. However, P involved in energy transfer
- Plants are unable to complete its lifecycle if the element is absent.
- Deficiency symptoms in the plant of the element can only be corrected by the supply
- of the particular element.
Crop nutrition
Proper nutrition is essential for satisfactory crop growth and production. The use of soil tests can help to determine the status of plant available nutrients to develop fertilizer recommendations to achieve optimum crop production. There are at least 17 elements known to be essential for plant growth.
Essential elements
Plants need 17 elements for their growth and completion of their life cycle. They are
- Carbon
- Hydrogen
- Oxygen
- Nitrogen
- Phosphorus
- Potassium
- Calcium
- Magnesium
- Sulphur
- 10.Iron
- Manganese
- Zinc
- Copper
- Boron
- Molybdenum
- Chlorine
- Nickel
- In addition to the 17 essential nutrients several elements are beneficial to some plants but are not considered necessary for completion of the plant life cycle. These are Cobalt (Co), Sodium (Na), Silicon (Si), Selenium (Se), Vanadium (V) and Aluminium (Al).
Classification of nutrients
On the basis of quantity of nutrient required:
- Basic nutrients: These constitute 96% of total dry matter of plant. e.g. Carbon, Hydrogen and Oxygen. Among these, carbon and oxygen constitute 45% each and hydrogen is 6%.
i) Macro nutrients: The nutrients which are required by plants in large quantities are called macro or major nutrients. These are six in number like Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sulphur, .
Macro nutrients have again two categories:
- Primary nutrients: Nitrogen, Phosphorus and Potassium.
- Secondary nutrients: Calcium, Magnesium and Sulphur.
ii) Micro nutrients: These nutrients required by plants in small quantities and also known as minor or trace elements. These are Manganese, Iron, Zinc, Copper, Boron, Molybdenum Chlorine and Cobalt.
Functions of plant nutrients:
- Carbon (C): It is the basic molecular component of carbohydrates, protein, lipids and nucleic acids.
- Oxygen (O): It is somewhat like carbon in that it occurs in virtually all organic compounds of living organisms.
- Hydrogen (H): Play a certain role in plant metabolism. Important in ionic balance and as main reducing agent plays a key role in energy relation of cells.
- Nitrogen (N): Nitrogen is needed for vigorous vegetative leaf and stem growth and dark green leaf colour (chlorophyll production).
- Phosphorus (P): Phosphorus is very mobile in plants; relatively immobile in soil and does not leach. It is stored in seeds and fruit. It is most readily available to plants between a pH of 6 and 7.5 (unavailable in very acid or alkaline soils). It has a central role in energy transfer and protein metabolism.
- Potassium (K): Potassium (potash – K2O) is highly mobile in plants, and generally immobile in soil. It tends to leach. Potassium promotes vigour and disease resistance, helps development of root system, improves plant quality.
- Calcium (Ca): Calcium is immobile in plants, and relatively immobile in soil. It is moderately leachable. Calcium is necessary for cell elongation and division, increases calcium content of plant.
- Magnesium (Mg): Magnesium is mobile in plants, mobile in acid soils, and fairly immobile above pH 6.5. It leaches from soil. Magnesium is necessary for formation of sugars, proteins, oils, and fats.
- Sulphur (S): Sulphur is necessary to maintain dark green colour, stimulate seed production, and promote root and general plant growth. It is part of proteins, amino acids, and vitamins, important in respiration.
- Iron (Fe): Iron is immobile in plants and mobility decreases in soil with increasing pH. Iron is necessary for chlorophyll maintenance.
- Zinc (Zn): Zinc is important for plant enzyme system function, seed production, and starch production. It needed for auxin synthesis.
- Zinc (Zn): Zinc is important for plant enzyme system function, seed production, and starch production. It needed for auxin synthesis.
- Manganese (Mn): Manganese involved in oxygen evolving system of photosynthesis. Manganese increases availability of Ca, Mg.
- Copper (Cu): Copper is a constituent of enzyme systems. It is involved in photosynthesis and respiration and the formation of lignin. It has indirect effect on nodule formation.
- Molybdenum (Mo): Molybdenum is needed for enzyme activity in the plant and for nitrogen fixation in legumes. It is an essential component of enzyme nitrate reductase in plant.
- Boron (B): Primary functions of B in plants are related to cell wall formation and reproductive tissue. It is necessary for nodule formation in legumes.
- Chlorine (Cl): Chlorine is required by the plant for leaf turgor and photosynthesis.
- Nickel (Ni): Nickel is required by plants for proper seed germination and is beneficial for N metabolism in legumes and other plants.
