Blue-green algae are photoautotrophic, prokaryotic algae. They are free living creatures and also known as Cyanobacteria. It fixes the atmospheric nitrogen in moist soils. So BGA has been recommended as a biofertilizer. The algae includes unicellular as well as filamentous species. Some of the filamentous forms have specialized cells known as heterocysts.Eg-Nostoc, Anabaena etc.These cells are the site of nitrogen fixation. The species which have heterocysts are known a heterocystous and those which don't have are known as non-heterocystous species. Among them only a few species can reduce N2 in to NH3.

How it is produced?

5 gm of top soil is taken from a paddy field and added in to a 100ml of fogg's medium in a flask. The flask is shaken well and incubated at room temperature. Now the illumination of 1500 lux is provided to the culture to increase the algal growth. Now the algal culture is transferred to 10ml of water in a tube with the help of a loop.Tube has to be shaken well so that algal filaments can be separated. The content is serially diluted. Every dilution drop is inoculated into Fogg's medium to establish algal growth. This process is executed in a petridish.

Fogg's medium-

KH2PO2 - 0.2 g; MgSO4.7H2O - 0.2 g; CaCl2 - 0.1 g; Na2MoO4 - 0.1 mg; MgCl2 - 0.1 mg; H3BO3 - 0.1 mg; CuSO4 - 0.1 mg; ZnSO4 - 0.1 mg; Fe-EDTA - 1.0 ml; Distilled water - 100 ml; pH - 7

A drop from each culture is examined microscopically. If it is supposed to be a pure culture for a single species then only, it is used further. In case of more than one species, the sample is diluted till the isolation of a pure culture is attained.

The pure cultures of BGA are transferred to culture flasks having Fogg's medium for growth. To favour the growth sufficient light is provided. Now the algal cultures are used as starter cultures. This initiates the mass culture of BGA. It can be processed in four ways:

Trough Method- In laboratory Zinc and Iron troughs are used. These are of 2*3 size and 22 cm height. The trough is filled with 10-12kg of soil and 200gm of super phosphate is spread on the soil. Now up to 5-15cms height water is poured. Calcium carbonate is added to adjust the pH around 7. Saw dust is provided to the soil. Now the starter culture is sprinkled over it. Trough is kept in sunlight where the BGA is developed very nicely. It is watered evereday. After sufficient response means nice growth of BGA the soil is allowed to dry. These dry flakes are collected and packed for algalization.

Pit Method- Under full sunlight shallow pits are maintained. To avoid the perlocation polythene sheets is lined inside the pit. The soil is filled in pit for 20cms and watered for 10 cm height. After maintaining the pH , carbofuran is added to the pit. Then saw dust is spread over the soil and is sprinkled with the starter culture. The pits are watered to favour the BGA growth. Thereafter, the soil is allowed to dry.

Field Method- In an open field small plots of 40 sq mts are maintained. The plot is watered upto 15cms height and 20 kg superphosphate is added to it. After correcting the pH 240 gm carbofuran is spreaded in the field. Now the starter culture (5kg) is provided to the plot and is frequently watered. In 3-4 weeks BGA developed and then soil is allowed to dry. In this method, 30 kg of BGA inoculant can be harvested.

After harvesting well dried BGA is packed. The bags are stored in cool dry place. These BGA bags can be preserved for 3 years with out loosing its efficiency.

A 10 kg of BGA inoculants is recommended for one hectare of flooded rice.The dried BGA flakes are introduced to the field after 10 days implantation. The application of BGA to the crops is called algalization. It increases the yield up to 34 percent in rice fields.

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