Role of nutrients and their deficiency Symptoms 

Nitrogen

• Impart green colour to plant encourages vegetative growth

• Nitrogen is essential constituent of protein

• Constituent of Protoplasm of chlorophyll and coenzyme.

• Play important role in synthesis of auxin

Deficiency

• Lower leaves become yellow and dries.
• V shaped chlorosis on older leaves or yellowing at tip.

Disease

• Starvation disease due to nitrogen deficiency.
• Buttoning in cauliflower.

Phosphorous

• Increase the disease resistance.
• Enhance new cell formation and necessary for root development.
• Required for grain formation and maturity of grains.
• Phosphorus is essential constituent for nucleic acid and phytin.
• Most essential functions are energy storage and transfer energy act as "energy currency".

Deficiency

• Due to deficiency of single element the life cycle of plant can't be completed hence (Agricultureexamslibrary) Phosphorus is called " key of life "
• Deficiency imparts dark green colour in leaves.
• Later develops red purple colourration.

Disease

• Sickle leaf diseases.

Potassium

• Most essential function of K+ is stomata regulation.
• Provides disease resistance in plants.
• Cofactor for enzymes.
• Formation and translocation of Sugars.
• Helps in chlorophyll formation.

Deficiency

• Spot of dead tissue at tips.
• Scorching and burning on margins of autumn leaves.

Disease

• Rottle/ dieback disease.

Calcium

• It is constituent of cell wall
• Calcium is a mobile in plants and deficiency symptoms appear on Meristem tip portion.

Deficiency

• Terminal bud die

 Disease 

• Tip hooking.
• Blossom end rot of tomato(BER).
• Popping in groundnut.

Magnesium

• Essential constituent of chlorophyll.
• Magnesium is a constituent of chlorophyll.
• Chlorosis between veins.

Disease 

• Sand -drown disease of tobacco.

Sulphur 

• Sulphur oxidizing Bacteria is Thiobacillus.
• Sulphur is essential for oil seed and pulses because it improves oil content and protein content in oil seeds and pulses, respectively.

Disease

• Akiochi disease of rice due to Excess of hydrogen sulphide.
•  Tea yellow disease of tea.

Iron

• Fe is the component of nitrate reductase.
• Required for nitrogen fixation.
•  During respiration act as O2 carrier.

Deficiency

• Interveinal complete chlorosis.
• Scorching of leaf margin.
• Yellowing of iron chlorosis in groundnut.

Manganese 

• Formation of chlorophyll.
• Co-factor of enzyme.
• Mn toxicity causes crinckle leaf of cotton.

Deficiency 

• Dead spot on leaves.

Desease

• Marsh spot of pea.
• Pahala blight of sugarcane.

Copper

• Compound of plastocyanin.
• Essential for photosynthesis/ respiration. 
• Dieback and reclamation disease of cereals.

Boron

• Necessary for Pollen germination.
• Boron is the only non-metal element among the micronutrient.
• It is necessary for translocation of Sugars and is involved in reproduction and germination of pollen.

Disease : 

• due to deficiency
• Browning of cauliflower is caused by Boron deficiency.
• Top sickness of tobacco.
• Fruit cracking of tomato.
• Hard fruit of citrus.
• Hen and chick disease of grape.

Zinc 

In plants it is required for biosynthesis of hormones.

Zn deficiency causes-

• White bud of maize.
• Khaira disease of rice.
• Little leaf of cotton.
• Mottled leaf of citrus.
• Rosette formation.

Cobalt 

• It is component of Vitamin B
• It is essential for formation of type of hemoglobin in N-fixing nodule tissue known as leghaemogloin.
• Act as O2 carrier in roots.
• Also known as animal protein factor.

Molybdenum

• Mo: absorbed as molybdate MoO4-2 forms.
• Mo is important component of enzyme: Nitrate reductage.
• N-fixation in pulses.
• Whiptail of cauliflower is due to deficiency of Mo.
• Mo is required for carrot & raphanus for sweetness.