Soil Nutrition class 11 agricultural
Introduction to nutrition:
The supply and absorption of chemical compounds needed for growth and metabolism of an organism.
Nutrient
Nutrients are substances required by an organism for their normal growth and reproduction.
Plant Nutrient
The plant nutrient is a “food” which is composed of certain chemical elements often referred to as‘plant nutrient’ or plant food elements considered very essential for growth and development of plants.
Essential nutrients and their categories according to plant needs The elements needed by the plant without which the plant is not able to survive and complete its life cycle are called essential nutrient.
Plants absorb or utilize more than 90 nutrient elements from the soil and other
sources during their growth and development and about 64 nutrients have been identified in plants by their tissue analysis. But all are not essential for their growth and development. They require only 17 elements/nutrients. These 17 have been recognized as essential elements. They are Of these element C,H,O together constitute 95-96% (C-45%, O-45%,H-6%).
Subsequently N, P and K constitute 2.7% in plants. The other elements constitute only 1.3-1.4%. But all have definite roles to play in the growth and development.
Among these Nickel is the latest nutrient addition to the list in 1987.
Essential nutrients are classified into two major groups based on relative utilization or absorption by the plants.
They are
A. Macro or Major Nutrients
B. Micro nutrients
A. Macro or Major Nutrients
They are the nutrients utilized by the plants in relatively large amounts (quantity) for their growth and development. Eg; C, H. O. N, P, K, Ca, Mg and S (C, H and O are abundantly present in the atmosphere and need not be applied through fertilizers).
Primary nutrients
Primary nutrient are those nutrients required relatively in large quantities by the plants for their growth and development. These are also designated as ‘fertilizer elements’ because, deficiency of these elements is corrected by application through fertilizers.
Eg: N, P and K
Secondary nutrients
Secondary nutrients are those nutrients which are required by plants in moderate amounts. They are called secondary because they are unknowingly supplied through fertilizers and other amendments. However their role in nutrition is not secondary but they are given secondary importance in its supply and management.
Eg: Ca, Mg and S
B. Micronutrients
The nutrients which are required by plants in relatively smaller quantities for their growth and development, but these are equally important and essential to plants as macronutrients. They are also called as trace/rare/nano elements. These include Fe, Mn, Zn, Cu, B, Mo, Cl and Ni.
Criteria of Essentiality of Nutrients for Plants
This concept was propounded by Arnon and Stout (1939) and refined by Arnon
(1954) and they considered 16 elements essential for plant nutrition. For an
element be regarded as an essential nutrient, it must satisfy the following criteria;
1. Plant cannot complete its life cycle in the absence of that element.
2. The action of element must be specific; no other element can wholly
substitute for it.
3. The element must be shown to be directly involved in the nutrition of plant,
that is, to be a constituent of an essential metabolite or at least required for
the action of essential enzymes.
Function and deficiency symptom of nutrient
Deficient
When an essential element is at a low concentration in plant that severely limits
the plant growth and produces more or less distinct deficiency symptoms on
plants. Under such conditions the yield of crop will be low / the quality of produce will be inferior.
Insufficient
When the level of an essential nutrient is below their actual content in plant or
available in an inadequate amounts that also affects the plant growth and
development.
Toxic
When the concentration of an element in plants is very high this affects the plant growth severely and produces toxicity symptoms on plants.
Excessive
When the concentration of an essential nutrient is sufficiently high but not toxic. It results in a corresponding shortage of other nutrients.
Functions of Carbon, Hydrogen and Oxygen
Carbon, Hydrogen and Oxygen form about 95% of the dry weight of plants and
are obtained from CO2 and H2O. They are converted into simple carbohydrates by photosynthesis and ultimately elaborated into complex amino acids, proteins and protoplasm. These are the major components of carbohydrates, proteins and fats.
Functions
- They play a dominant role in the process of photosynthesis and respiration
in plants.
- They are involved in the formation of simple as well as complex organic
compounds like carbohydrates, starch proteins etc.
- Maintaining the structure of the plant cells.
- They provide ‘energy’ required for the growth and development of plant by oxidative break down of carbohydrates, proteins and fats during their
cellular respiration.
Functions and deficiency symptoms of Nitrogen
Nitrogen plays a key role in the nutrition of plants. It is one of the principal
growth promoting nutrient elements. Green plants are more markedly influenced by the deficiency of nitrogen than by any other element. It is absorbed by plants in the ionic form of NO3-, by most of the plants. Some plants require NH4+ form (rice). When applied as foliar nutrition, NH2 (amide from) is also absorbed. It has got most recognized role in the plant metabolism as it performs the following vital functions.
Functions
- The Nitrogen is mainly involved in Photosynthesis of plants as it is essential
constituent of chlorophyll, a green pigment essential in photosynthesis.
- It is very basic constituent of plant life, because, it forms essential
constituent of proteins, nucleotides phosphatides, alkaloids, enzymes,hormones, vitamins etc.,
- It promotes better Vegetative growth and adequate supply of nitrogen
promotes rapid early growth and imparts dark green color to plants,
improves quality and succulence of leafy vegetables and fodder crops.
- It stimulates the formation of fruit buds; increases fruit set, and improve quality of fruits.
- It governs the better utilization of Potassium, Phosphorus & other elements.
Deficiency symptoms
Nitrogen is a highly mobile element in plants and so deficiency is exhibited in older/ bottom leaves. The striking deficiency symptoms are
- Yellowing of older leaves due to inhibition of chloroplasts and chlorophyll
synthesis. As the deficiency of Nitrogen becomes severe “Chlorosis” of
leaves is observed.
- Plants become dwarfed or stunted growth.
- Tends to advance the time of flower bud formation and reduce yield.
- Fruits become hard, small, low bearing capacity of trees,
- Reduces fertilization, premature dropping and fruits may become seed less.
- Severe deficiency leads to Necrosis of plant leaves (complete death of leaf).
Excessive or Toxicity
Excessive N in plants leads to more vegetative growth. Leaves become more succulent and more susceptible to pest and disease attack. Lodging of plants may occur. Reduces the sugar content of plant, storage and keeping quality of fruits or leaves and prolong the growing period and delay the reproductive phase of plant and crop maturity.
Phosphorus
Phosphorous is a constituent of essential cell components such as phytins,phosphoproteins, phospholipids, nucleic acids (DNA, RNA), co-enzymes (NAD& NADP), ATP and other high energy compounds. It is also a structural component of cell membrane, chloroplasts, mitochondria and meristematic tissues. Plants absorb Phosphorus as H2PO4 -and HPO42- ionic form. Phosphate compounds act as “energy currency” within plants. It is highly mobile in plants but immobile in soils.
Functions
- Involved in energy storage and transfer. Also carry various metabolic processes in plants.
- Involved in cell division and development of meristematic tissue and thus it improves better vegetative growth of plants.
- Important for root development and stimulates root growth.
- Helps in primordial development, flowering, seed formation, ripening of fruits, germination of seeds and also early maturity of crops.
- It is essential for formation of starch, proteins, nucleic acids, photosynthesis,nitrogen-metabolism, carbohydrate metabolism, glycolysis, respiration and fatty acid synthesis.
Deficiency symptoms
- Stunted and slow growth of plants due to its effects on cell division andmeristematic tissue development.
- Leaves are small and defoliation starts from the older leaves and premature leaf fall.
- Purplish discoloration of foliage due to anthocyanin pigment. Plants develop
dead necrotic areas on the leaves, petioles or fruits.
- Slender and woody stem with under developed roots are characteristics symptoms.
- Delay in flowering and ripening of fruits, inferior quality, shedding of
blossom, inflorescence becomes small and premature fruit falling.
- Inhibit the sugar synthesis or abnormally high sugar levels in plant.
Potassium
Potassium is indispensable in the plant nutrition and needs to be supplied in relatively large quantities to fruit crops and field crops. Plants absorb K from the soil as K+ ion and it is mobile in nature in plants. Potassium does not enter into the composition of any of the constituents of the plant cells such as proteins, chlorophyll, fats and carbohydrates. It primarily occurs as soluble inorganic salts and occasionally as salts of organic acids. It is abundant cation in the cytoplasm, meristematic regions, cell sap. It is considered as quality element for many crops.
It exists in mobile ionic form and it functions appear to be catalytic in nature, thus called "Chemical Policeman" of plants.
Functions
- Potassium is responsible for osmoregulation and controls cell turger pressure.
- It has an important role in pH stabilization, enzyme activation, protein
synthesis, stomata movement (closing and opening), cell extension and photosynthesis.
- Impart drought/heat/frost resistance to plants as it regulates transpiration and water conditions in the plant cell. It improves water use efficiency
- Impart pest and disease resistance to plants
- Required for ATP synthesis and better N use efficiency by favoring the protein formation.
- Plants become strong and stiff; thus it reduces lodging of plants.
- Essential in the formation and transfer of starch and sugars especially in potato, sweet potato, turnip, banana, tapioca.
Deficiency symptoms
- Weakening of stem and lodging of crops and easy susceptibility to pest and diseases.
- Scorching of leaves and burning appearance of leaf margins and tip
- Poor keeping quality of fruits. The quality of fruits and vegetables decreases.
- Marginal necrosis and burning of leaf tips.
- Stunted growth, shortening of internodes.
- It causes great disturbance in the water economy of plants and more water is
lost per unit dry matter.
- Poor sprouting of vines.
- Severe attack of the grapes with Botrytis cinerea due to K deficiency.
- small tubers in potato due to low sugar occumulation.