Biofertilizer Blue-Green Algae (Cyanobacteria)
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.
Table 12.5. Contribution of nitrogen by some of the nodulated legumes when used as green manure/cover crop.
N2 fixing system | Amount of N contributed (q/ha) | |
1. | Green manure legumes : | |
Sesbania aculeata – Rhizobium | 70-120 | |
Leucaena leucocephala - Rhizobium | 500-600 | |
Beans (broad beans / lupines /soybean / lentil, etc.) - Rhizobium | 60-210 | |
Fodders (Trifolium / Medicagol Melilotus, etc. ) - Rhizobium | 100-300 | |
2. | Cover crop legumes : | |
Lablab purpureus - Rhizobium | 240 | |
Glycine jawanica - Rhizobium | 210 | |
3. | Non-legumes : | |
Casuarina equisitifolia - Frankia | 100 | |
Alnus - Frankia | 30-300 | |
4. | Others : | |
Azolla - Anabaena | 25-190 | |
Grasses - Azospirillium | 15-100 |
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:
(i) | Prepare the cemented tanks, shallow trays of iron sheets or polythene lined pits in an open area. Width of tanks or pits should not be more than 1.5 m. This will facilitate the proper handling of culture. |
(ii) | Transfer 2 -3 Kg soil (collected from open place for lm 2 area of the tank) and add 100 g of superphosphate. Water the pit to about 10 cm height. Mix lime to adjust the pH 7. Add 2 ml of insecticide e.g. malathion to protect the culture from mosquitoes. Mix well and allow to settle down soil particles. |
(iii) | When water becomes clear, sprinkle 100 g of starter inoculum on the surface of water. |
(iv) | When temperature remains between 35-40° during summer, optimum growth of cyanobacteria is achieved. Always maintain the water level to about 10 cm during this period, |
(v) | After drying, the algal mat will get separated from the soil and forms flakes. During summer about 1 kg pure algal mat per m2 area is produced. These are collected, powdered, kept in sealed polythene bags and supplied to the farmers. |
(vi) | The algal flakes can be used as starter inoculum if the same process is repeated. |