Biologically active products or microbial inoculants of bacteria, algae and fungi, which may help biological nitrogen fixation for the benefit of the plants, are defined as Biofertilizers. Biofertilizers include the following (i) Symbiotic nitrogen fixers (Rhizobium spp.) (ii) asymbiotic free nitrogen fixers (Azotobacter, Azaspirillum etc.) (iii) Algae biofertilizers (blue-green algae etc.) (iv) Phosphate solubilizing bacteria (v) mycorrhizae and (vi) organic fertilizers.
The need for the use of biofertilizers has arisen primarily for two reasons:
(i) Increase in the use of fertilizers leads to increase in crop
(ii) Increased usage of chemical fertilizers leads to damage in soil texture and raises other environmental problems. Therefore, the use of biofertilizers is both economical and environment friendly. The pragmatic approach will be to develop the integrated nutrient supply system involving a combination of the use of chemical fertilizers and biofertilizers. India’s production of fertilizers is less than the required. Realizing the importance biofertilizers is supplementing the use of chemical fertilizers the Govt. of India launched the “National Project on Development and use of Biofertilizers”. Under this project on national centre at Ghaziabad, UP and six regional centers and 40 BGA (Blue0Green algae) production centers have been established.
Organisms which are biofertile: Rhizobium is a gram negative soil bacterium, which enters into symbiotic relation with legumes (pulses). Rhizobium fixes atmospheric nitrogen and increases the production of the crop and also leaves a fair amount of nitrogen in the soil, which benefits the subsequent crop in India. There are seven groups of Rhizobia which have been recognized for inoculating legumes. These are Rhizobium leguinosarum, Rhizobium melilotii, Rhizobium trifoli, Rhizobium phaseoli, Rhizobium lumpini, Rhizobim japonicum, and Rhizobium species. The nitrogen fixing ability of legumes inoculated with these Rhizobia range from 50 kg to 150 kg per hectare.
Asymbiotic Nitrogen fixers are Azotobacter and Azospirillum. When these are applied into the rhizospheric soil they fix atmospheric nitrogen and make it available for non-leguminous plants also synthesize growth promoting substances, which is helpful to the plants. Azotobacter fixes about 30 kg nitrogen and Azospirillum fixes about 25 kg of nitrogen.
Algal fertilizers: Blue green algae (BGA) and Azolla constitute a good system of biofertilizers, especially for low and paddy. Application of, dried blue green algae flakes applies at the rate of 10 kg per hectare is recommended ten days after transplantation of paddy. BGA which is providing nitrogen to the crop also provide the following advantages.
i. Algal biomass accumulates as organic matter.
ii. Growth promoting substances are produced, which stimulate growth of rice seeding.
iii. BGA helps in reclamation of saline and alkaline rails.
There are also some important new biofertilizers, such as Phosphate solubiliznig bacteria (PSB) e.g. Thiobcillus and plant growth-promoting rhizobacteria (PGPR) including Psdomonas fluorescens and Pseudomonas putida. PSBs convert non-available inorganic phosphates into soluble organic phosphates which can be utilized by crop plants. PGPRs produce sidrophores which chelate with iron and make it unavailable to harmful fungi. These biofertilizers are yet to be commercialized in our country.
Organic fertilizers include animal dung, animal urine, bone meals, slaughter house waste, crop residues, oil cakes, urban garbage, sewage effluent etc. Must of there organic wastes remain unutilized