Nitrogen Fixing Organisms

Some bacteria are known to fix the atmospheric nitrogen for their own biological activity. This natural phenomena is commercially utilized to increase the nutrient supply to crops.

There are two types of nitrogen fixing bacteria. They are

a) Symbiotic N₂ fixing bacteria - well known example of this type is Rhizobium.

b) Non-symbiotic N₂ fixing bacteria - For e.g., Azospirillium, azotobacter.

Symbiotic N₂ fixing bacteria fix nitrogen in association with roots of leguminous plants. They live in knot like structures called nodules on leguminous roots - where they live in symbiotic harmony with plants. They derive their source of energy from plants and in turn fix nitrogen - which is beneficial to plants. When such crops are harvested, the roots of such crops remain inside the soil - adding nitrogen and other nutrients to the soil.

Non-symbiotic N₂ fixing bacteria exist either freely in soil or on root surfaces without any symbiotic relations with roots. Such bacteria are found - where grasses, cereals are grown. They fix atmospheric nitrogen and make it available to crops.

Fixation of nitrogen by such bacteria may occur naturally in very ideal situation. But such fixation process may have to be enhanced by external application of bacterial culture to the soil. Such bacterial culture is usually supplied to soil in small dosage as starter dosage - which is later multiplied and bacterial population in soil increases so much that soil adequately gets fixed nitrogen. Application of bacterial culture of Rhizobium, Azotobacter and Azospirillium is commonly followed in many crops. Such culture is called biofertilizer. Bacteria cultures are reported to have increased the crop yields by 10-25% in different crops.