Biofertilizer Blue-Green Algae (Cyanobacteria)

Role of the blue-green algae (e.g. Aulosira, Anabaena, Cylindrospermum, Nostoc, Plectonema, Tolypothrix) in the paddy fields was realized much earlier (Singh, 1961). In water-logging condition, the cyanobacteria multiply, fix atmospheric N₂ and release it into the surroundings in the form of amino acids, proteins and other growth promoting substances (Sewart, 1970). Recent works done at Central Rice Research Institute, (Cuttack), Indian Council of Agricultural Research (New Delhi) and other centres, e.g. Centre of Advanced Study in Botany, Banaras Hindu University, Varanasi are of much importance.

Algalization
It were Japanese workers (Watanabe and coworkers) who developed techniques for mass cultivation of blue-green algae to be used as biofertilizer in paddy fields. Venkataraman (1961) coined the term 'algalization' to denote the process of application of blue-green algal culture in field as biofertilizer. He initiated algalization technology in India and demonstrated the way how this technology could be transferred to farmer level who hold small lands (Vekataraman, 1972).

At present, algalization is being followed in Tamil Nadu and Uttar Pradesh, and tried in Jammu and Kashmir, Andhra Pradesh, Karnataka, Maharashtra and Haryana. Algalization is also being practiced in China, Egypt, Philippines and erstwhile U.S.S.R.

In 1990, Department of Biotechnology, Government of India, New Delhi establishment four major centres in different paddy growing areas of the country for acceleration and extension of works on algal biofertilizers. The programme was launched under 'Technology Development and Demonstration Projects on Cyanobacterial Biofertilizers' in U.P. (Lucknow), Tamil Nadu (Madurai), West Bengal (Calcutta) and New Delhi. The main objectives of the programme were (i) to develop low cost indigenous technology for mass production of cyano bacteria, (ii) to isolate regional specific fast growing and better N₂ - fixing strains, (iii) to develop starter inoculum, (iv) to demonstrate the farmers in field, and (v) to study the benefits on both economy and ecology. As a result of these studies cyanobacterial biofertilizer was found very useful, especially for small and marginal farmers of the country with the view point of both economy and ecology (Venkataraman, 1993).

Table 12.5. Contribution of nitrogen by some of the nodulated legumes when used as green manure/cover crop.
Source : Ghai and Thomas (1989).

D.B.T. Centre of U.P. (Lucknow) has reported the increase in yield of paddy (about 12.5 q/ha) to be due to cyanobacterial biofertilizer. Moreover, its use continued with chemical fertilizer gave the best results. Because the cyanobacterial biofertilizer not only increase the productivity and quality of paddy, but also minimize the harmful effects of the chemical fertilizers.

Mass cultivation of cyanobacterial biofertilizers
For outdoor mass cultivation of cyanobacterial biofertilizers, the regional specific strains should be used. However, many germplasm collection laboratories have been established by the D.B.T. in different parts of the country for the development of starter inoculum. Mixture of 5 or 6 regional acclimatized strains of cyanobacteria, e.g. species of Anabaena, Aulosira, Cylindrospermum, Gloeotrichia, Nostoc, Plectonema, Tolypothrix are generally used for starter inoculum. The following four methods are used for mass cultivation : (i) cemented tank method., (ii) shallow metal troughs method, (iii) polythene lined pit method, and (iv) field method. The polythene lined pit method is most suitable for small and marginal farmers to prepared algal biofertilizer. In this method, small pits are prepared in field and lined with thick polythene sheets. Mass cultivation of cyanobacteria is done by using any of the four methods under the following steps: