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Agriculture LibreTexts

Section B

Role of Macro- and Micro-nutrients and Their Deficiency symptoms

Name of elements Element obtained in the form of Regions of plant where element required Functions Deficiency symptoms
Macronutrients
Nitrogen (N) Nitrogen can exist in a soil organic form, or as an ammonium ion (NH4+)nitrite ion (NO2-),or nitrate ion (NO3-). Nitrogen is required by all parts of a plant, particularly the meristematic tissues and the metabolically active cells. Nitrogen is one of the major constituents of proteins, nucleic acids, vitamins and hormones, coenzymes, and nucleotides.Nitrogen promotes rapid growth, increases leaf size and quality, hastens crop maturity, and promotes fruit and seed development. Reduced growth, yellowing (chlorosis), reds and purples may intensify with some plants, reduced lateral breaks.
Phosphorus (P) Phosphorus is absorbed by the plants from soil in the form of phosphate ions as H2PO4-orthophosphate. Phosphate is easily redistributed in most plants from one organ to another and is lost from older leaves, accumulating in younger leaves, developing flowers and seeds.The meristem region of growing plants is high in phosphorus. Phosphorus is a constituent of cell membranes, certain proteins, all nucleic acids and nucleotides, involved in energy transfer such as ATP and ADP. It activates coenzymes for amino acid production used in protein synthesis;and it is involved in many other metabolic processes required for normal growth, such as photosynthesis, glycolysis, respiration, and fatty acid synthesis. Stunted growth, dark green leaves with a leathery texture, and reddish purple leaf tips and margins.Maturity is often delayed.
Potassium (K) It is absorbed as potassium ion (K+). Required in more abundant quantities in the meristematic tissues, buds, leaves and root tips. Helps to determine an anion-cation balance in cells and activates enzymes to metabolize carbohydrates for the manufacture of amino acids and proteins, opening and closing of stomata, activation of enzymes and in the maintenance of the turgidity of cells, facilitates cell division and growth by helping to move starches and sugars between plant parts,disease resistance. Small plants, brown margins on lower leaves, small weak stems, lodging of plants, poor yield and quality.As in N and P, K+ is easily redistributed from mature to younger organs, so symptoms first appear in older leaves.
Magnesium (Mg) It is absorbed as magnesium ion (Mg2+). It is used for fruit and nut formation and essential for germination of seeds. Leaves: withdrawn from ageing leaves and exported to developing seeds is a critical structural component of the chlorophyll molecule and is necessary for functioning of plant enzymes to produce carbohydrates, sugars and fats.It is an enzyme activator in the synthesis of nucleic acids (DNA and RNA). Extensive interveinal chlorosis which starts with basal leaves and progresses to younger leaves (it is mobile).
Calcium (Ca2+) It is absorbed as calcium ion (Ca2+).Adsorbed Ca2+ is important for soil structure by promoting the aggregation of soil particles. This improves water and root penetration through the soil and maintains the stability of soil particles. Meristematic and differentiating tissues. It is immobile (non-translocatable) within plants and remains in the older tissue throughout the growing season.Calcium is easily leached. Calcium is involved in many plant processes, including cell elongation, cell division, germination, pollen growth, activates enzymes,and is a structural component of cell walls, . One of its most important functions is the maintenance of membrane permeability and cell integrity. Inhibition of bud growth, death of root tips, cupping of mature leaves, weak growth.,
Sulphur (S) Sulfate (SO4=) from the soil is the primary source of S.Sulfur is also taken up by leaves in gaseous form as SO2. Stem and root tips young leaves; remobilized during senescence (the growth phase in a plant or plant part -as a leaf from full maturity to death). It is a structural component of amino acids, proteins, vitamins and enzymes and is essential to produce chlorophyll. General chlorosis of leaf, including vascular bundles.Sulfur is not easily mobilized within the plant.Therefore,chlorosis, occur in young tissues before older ones.
Micronutrient
Zinc -Zn (immobile) Most zinc in soil is found in different minerals with only a small percentage being adsorbed in ionic form on soil and organic matter exchange sites. Everywhere It activates various enzymes especially carboxylases, part of carbonic anhydrase and various dehydrogenases, needed for auxin synthesis. Interveinal chlorosis of the upper (youngest) leaves. Afterwards, shoot growth slows down, giving the affected plant parts a rosette-like appearance.
Manganese -Mn (Immobile) The most important form for uptake by roots is Mn++, but it is also commonly found as oxides of Mn+++ and Mn ++++(Mn2O3, MnO2, etc.). Leaves and seeds Manganese in the plant participates in several important processes including photosynthesis and nitrogen and carbohydrate metabolism. The absence of Manganese causes disorganization of chloroplast thylakoid membranes. Chlorosis
Iron, Fe (Immobile) Plants obtain iron in the form of ferric ions (Fe3+). It is required in larger amounts as compare to other micronutrients. Everywhere , collects along leaf veins. Important constituent of proteins involved in the transfer of electrons like ferredoxin and cytochromes, reversibly oxidised from Fe2+ to Fe3+ during electron transfer,activates catalase enzyme, required for synthesis of chlorophyll. Extensive interveinal chlorosis, starting with younger leaves (iron is relatively immobile).
Copper (Cu) It is absorbed as cupric ions (Cu2+). Everywhere Essential for the overall metabolism in plants.More than half of the copper is located in the chloroplasts and participates in photo-synthetic reactions. It is also found in other enzymes involved with protein and carbohydrate metabolism. Dieback of shoots
Molybdenum (Mo) Plants obtain it in the form of molybdate ions. Everywhere, the synthesis of proteins is blocked and plant growth ceases. Root nodule (nitrogen fixing) bacteria also require it. Seeds may not form completely, and nitrogen deficiency may occur if plants are lacking molybdenum. Essential component of two enzymes involved with nitrogen metabolism. Pale green leaves with rolled or cupped margins.
Boron (B) The soluble form is primarily boric acid (B(OH)3). In neutral to acid soils, boric acid has no charge and can, therefore, be easily leached. At higher pH values, conversion to B(OH)4- occurs. The resulting negative charge on the molecule causes its absorption by soil particles. Leaves and seeds Boron is required for uptake and utilisation of Ca2+, membrane functioning, pollen germination, cell elongation, cell differentiation and carbohydrate translocation. Terminal buds are damaged, leaving a rosette effect on the plant. Leaves are thick, curled and brittle. Fruits, tubers and roots are discolored, cracked and flecked with brown spots.
Chlorine (Cl) Chloride (Cl–), the ionic form of chlorine used by plants, is usually found in soluble forms and is lost by leaching.. Everywhere Involved in osmosis (movement of water or solutes in cells), the ionic balance necessary for plants to take up mineral elements and in photosynthesis. Reduced growth; stubby roots, interveinal chlorosis, nonsucculent tissue (in leafy vegetables)

Hunger Signs:- When plants do not get sufficient amount of one or more essential nutrient elements ,they show poor growth and develop specific deficiency symptoms Which is known as hunger signs.