Nitrogenous fertilizers produced in industry by Haber-Bosch process consume high energy (about 13,500 K Cal/Kg N fixed). In such industries, fossil fuel is the source of energy. In recent years, due to Gulf crisis, the cost of crude oil increased about three fold within a year. Therefore, fossil fuel (oil and coal) based method of farming has becoming more expensive accordingly. To combat with this problem, however, it is necessary to develop an alternative method of supplying nutrients to plants.
In recent years, use of microbial inoculants as a source of biofertilizers has become a hope for most of countries, as far as economical and environmental view points are concerned. Biologically fixed nitrogen is such a source which can supply an adequate amount of nitrogen to plants and other nutrients to some extent. It is a non-hazardous way of fertilization of field. Moreover, biologically fixed nitrogen consumes about 25 per cent to 30 per cent less energy than normally done by chemical process.
Therefore, in developing countries like India, it can solve the problem, of high cost of fertilizers and help in saving the economy of the country.
The term 'biofertilizers' denotes all the "nutrient inputs of biological origin for plant growth" (Subba Rao, 1982). Here biological origin should be referred to as microbiological process synthesizing complex compounds and their further release into outer medium, to the close vicinity of plant roots which are again taken up by plants. Therefore, the appropriate term for biofertilizers should be "microbial inoculants" as suggested by Subba Rao (1982). As bacteria and cyanobacteria (also Frankia) are known to fix atmospheric nitrogen, both bacteria and cyanobacteria are widely used as biofertilizer.