Biofertilizers

Any living organism supplying plant nutrients directly or indirectly is regarded as biofertilizer. They are not synthetically manufactured in factory. Many organisms with a potentiality to supply plant nutrients - have been recognised. Use of biofertilizers has many advantages.

They are:

• Biofertilizers are eco-friendly and do not cause pollution of air and water.

• Biofertilizers, besides supplying plant nutrients, build up the inherent capacity of soil to produce, retain and supply plant nutrients on sustainable basis.

• Biofertilizers need not be carried over long distances.

• Biofertilizers supply many micro nutrients like zinc, boron, molybdenum, sulphur, iron and calcium besides major nutrients like nitrogen, phosphorus and potassium. But chemical fertilizers generally supply only one or two nutrients at a time.

• They prevent soil erosion and loss of nutrients by leaching.

There are many types of biofertilizers, each one acting in its own specific way.

• Green manures

• Earthworms

• Nitrogen fixing organisms

• Azolla

• Blue green algae

• Phosphate solubalising bacteria

• Vascicular - arbiscular mycorrhizae

Green manures

Green manure refers to supplying the plant nutrients by application of living plant material to the soil. The nutrients are made available after decomposition of green manure in soil. Many plants have been identified for their potentiality as green manure.

The green manures are normally applied when they are succulent and tender so that they can easily decompose in soil. The green manures are incorporated into the soil by ploughing them. As the nutrients are made available entirely by biological sources they are popularly called as biofertilizers.

There are two systems in the use of green manures:

• To bring the green leaf from outside and incorporating them in the soil.

• To grow green manure crop on the land for cultivation, before the main crop is grown and incorporate the same in the soil before sowing the main crop.

The former system is usually followed in green manure tree crops such as Pongemia which are grown either on roadside or in forests. The greener part of these plants are cut and applied to cultivated field. The latter system is followed in other short duration green manure crops - which are grown on cultivated lands.

Most of green manure crops are leguminous and have capacity to fix nitrogen. Their use as green manure is advantageous - as this helps in meeting the nutrient demands of cultivated crop. Green manuring is reported to have increased the crop yields by 10 - 20%.

Earthworms

Earthworms have traditionally been known as friend of farmer. They were known as farmer's friend due to their lifestyle involving

• turnover of the soil - as the earthworms move up and down in the soil, they help in better aeration of soil and increase the permeability of soil.

• production of manure by eating away the organic wastes.

Recently, their potentiality to produce the manure is commercially exploited. Growing earthworms on commercial scale to produce the manure is called as VERMICULTURE and manure produced by it is called VERMICOMPOST. Earthworms work day and night to convert the organic wastes into a nutrient rich manure. Any decomposable organic waste can be used to produce VERMICOMPOST. Such manure contains all major nutrients like nitrogen, phosphorous and potassium besides many micronutrients.

Use of vermicompost improves soil characters, besides supplying nutrients. It also improves the microbial activity - as vermicompost adds organic matter. In turn, the soil regains its inherent capacity to produce, retain and supply nutrients to crops on a sustainable basis. Vermicompost can increase the crop yields by 20 - 30%.