• Biofertilizers are carrier-based preparations containing effective strains of microorganism like. Bacteria” algae, fungi alone- or in combination in sufficient numbers which can provide plant nutrients through microbial activity. ‘
• The biofertilizers are grouped in three main categories according to the nutrients provided by biofertilizers.
• 1. Biofertilizers for nitrogen fixation.
• 2. Biofertilizers for phosphate solubilization.
• 3. Biofertilizers for decomposing organic matters.

When these microorganisms are incorporated with seeds/seedlings and in soil they ensure enhanced crop production by way of  Biological Nitrogen Fixation, solubilisation of fixed phosphate, uptake of P & other mineral nutrients and synthesis of growth promoting substances.

• For better crop yield, nitrogen is most essential plant nutrient, since it is widely consumed by majority of plants, most of soils are deficient in it.
• Although air contains about 80% nitrogen but plants cannot make use of it as such.
• The three types of bacteria i.e. Symbiotic, Non-symbiotic, free living and associative are useful to reduce molecular form of atmospheric nitrogen into ammonia(NH3) which is assimilated by the plants .
• These are called Nitrogen fixing bacteria.