Role and Deficiency Symptoms of Plant Nutrients

Primary Macronutrients

Nitrogen (N)

🔹 Absorbed Form: Nitrate (NO₃⁻) & Ammonium (NH₄⁺)

🔹 Functions / Role:

• Major constituent of amino acids, proteins, enzymes, chlorophyll, nucleic acids (DNA/RNA), and coenzymes.
• Promotes vegetative growth, especially in leafy vegetables.
• Enhances chlorophyll content and photosynthesis.
• Improves forage quality in fodder crops.

🔹 Deficiency Symptoms:

• Older leaves first affected.
• Uniform chlorosis (yellowing) of older leaves including veins.
• Leaves become stiff and erect.
• In cereals: ‘V’-shaped yellowing from tip toward base.
• Poor tillering, reduced growth and yield.

Phosphorus (P)

🔹 Absorbed Form: H₂PO₄⁻ (in acidic soil). HPO₄²⁻ (in neutral to alkaline soil)

🔹 Functions / Role:

• Essential for energy transfer reactions (ATP, ADP).
• Integral part of nucleic acids and phospholipids.
• Promotes early root development and seed/fruit formation.
• Stimulates flowering and maturity.
• Required for nitrogen fixation in legumes.

🔹 Deficiency Symptoms:

• Older leaves affected first.
• Leaves become small, dark green, erect, and may show purplish/reddish tinge.
• Bronze or bluish-green tint on the underside of leaves.
• Delayed maturity and poor root development.
• Reduced flowering and seed set.

Potassium (K)

🔹 Absorbed Form: K⁺ (Potassium ion)

🔹 Functions / Role:

• Activates over 60 enzymes involved in growth and metabolism.
• Regulates stomatal opening and water balance.
• Improves disease resistance, lodging resistance, and cold tolerance.
• Essential for translocation of sugars and starch.
• Enhances fruit quality, size, color, and taste.

🔹 Deficiency Symptoms:

• Older leaves show symptoms first.
• Chlorosis along leaf margins followed by necrosis (dead tissues).
• Leaf tip and margin scorching (leaf burn).
• Upward curling of leaves.
• In fruits: poor development, reduced color and taste.
• Barley is very sensitive; cotton shows small bolls and poor opening.

Quick Comparison Table (for Revision)

Secondary Macronutrients

Calcium (Ca)

• Role:
  • Component of cell walls (calcium pectate).
  • Essential for cell division and growing points.
  • Maintains membrane integrity and neutralizes organic acids.
• Deficiency symptoms:
  • Dead shoot tips, distorted growth.
  • Poor root development and short roots.
  • Blossom end rot in tomato.

Magnesium (Mg)

• Role:
  • Central atom in chlorophyll.
  • Involved in enzyme activation, starch translocation, and fat/oil synthesis.
• Deficiency symptoms:
  • Interveinal chlorosis in older leaves.
  • Premature leaf fall.
  • Reduced photosynthesis.

Sulphur (S)

• Role:
  • Component of amino acids (methionine, cysteine), vitamins.
  • Required for chlorophyll formation and enzyme stability.
• Deficiency symptoms:
  • Yellowing of young leaves (not older).
  • Thin, small leaves, reduced nodule formation.
  • Top sickness in tobacco, whiptail in cauliflower.

Micronutrients

7. Iron (Fe)

• Role: Needed for chlorophyll synthesis, respiration, electron transport. Component of cytochromes, ferredoxin.
• Deficiency symptoms:
  • Interveinal chlorosis in young leaves.
  • Khaira disease in rice.

8. Manganese (Mn)

• Role: Activates enzymes, essential for photosynthesis (Hill reaction). Produces SOD to protect chloroplasts.
• Deficiency symptoms:
  • Chequered chlorosis, especially in oat, soybean.
  • Grey speck of oat, Pahala blight of sugarcane.

9. Zinc (Zn)

• Role: Required for IAA synthesis, enzyme activity. Component of carbonic anhydrase, RNA polymerase.
• Deficiency symptoms:
  • White bud in maize.
  • Khaira disease in rice.
  • Interveinal chlorosis, rosetting.

10. Copper (Cu)

• Role: Part of electron transport chain (plastocyanin). Helps in SOD production, photosynthesis, lignin formation.
• Deficiency symptoms:
  • Twisting of young leaves, poor pigmentation.
  • Die-back in citrus, exanthema in trees.

11. Boron (B)

• Role: Important for cell wall integrity, sugar translocation, reproduction. Maintains apical dominance, affects Ca metabolism.
• Deficiency symptoms:
  • Brittle leaves, bud necrosis.
  • Cracked fruits, hollow stem in cauliflower.
  • Brown heart in beet.

12. Molybdenum (Mo)

• Role: Component of nitrogenase, involved in N-fixation. Aids in nitrate reduction.
• Deficiency symptoms:
  • Whiptail in cauliflower.
  • Poor N-fixation in legumes.

13. Chlorine (Cl)

• Role: Involved in photosynthesis, osmotic adjustment. Affects carbohydrate metabolism in tobacco.
• Deficiency symptoms:
  • Wilting, chlorosis.
  • Reduced root and leaf growth.

14. Nickel (Ni)

• Role: Component of urease enzyme. Essential for seed viability, N metabolism.
• Deficiency symptoms:
  • Poor grain filling, reduced seed germination.

15. Cobalt (Co)

• Role: Needed for vitamin B₁₂ (leghaemoglobin formation). Required by Rhizobium in legumes.
• Deficiency symptoms:
  • Poor nodulation, stunted legume growth.

16. Sodium (Na)

• Role: Essential for sugar beet, helps in water balance, can substitute K in some plants.
• Deficiency symptoms: Wilting, poor drought tolerance.

17. Silicon (Si)

• Role: Strengthens cell wall, increases resistance to pests/diseases. Improves grain quality, plant structure.
• Deficiency symptoms: Weak stems, disease susceptibility, especially in rice.

General Deficiency Identification