ALGAL BIOFERTILIZER

ALGAL BIOFERTILIZER

 

Blue Green Algae (BGA)

• Blue Green Algae (BGA) or Cyanobacteria are the Algal Biofertilizers involved in Free living nitrogen fixation.
• Blue-green algae are Prokaryotic, Filamentous in nature and Ubiquitous in distribution.
• BGA are either single celled or consist of branched or unbranched filaments.
• More than 100 species of Blue Green Algae (BGA) can fix atmospheric Nitrogen.
• In BGA, Nitrogen fixation takes place in specialized cells called ‘Heterocyst’.
• Recently, some BGA without Heterocysts have also been found to fix nitrogen under special conditions like low oxygen tension. The algae that are generally used for field application are species of Aulosira, Tolypothrix, Scytonema, Nostoc, Anabaena and Plectonema as a mixture.
• The BGA are abundantly present in the habitats wherein moisture and light are adequately available. 
• Though different groups of Algae are present, only certain groups of BGA fix atmospheric nitrogen and they can contribute significantly to the fertility of soils. 
• Nitrogen fixing BGA are grouped as Cyanobacteria besides fixing Nitrogen, these BGA excrete Vitamin B12, Auxins and Ascorbic acid which may also contribute to plant growth.
• BGA are very common in the Rice field. Unlike other Biofertilizers, BGA are not inhibited by the presence of Chemical fertilizers.
• Inoculation of BGA in Rice field can result in 10 to 14 % increase in crop yield. 

Important Genera of Blue Green Algae (BGA)

Anabaena sp., Nostoc sp., Cylindrospermum sp., Aulosira sp., Rivularia sp., Oscillatoria sp., Plectonema sp., Aphanothece sp., Lyngbya sp., Microcoleus sp., Gleocapsa sp., Microcystis sp., Scytonema sp., Westiellopsis sp. and Calotrhix sp.

Figure - 1: Morphology of some important genera of BGA

Target Crop - Rice

Method for Isolation of Blue Green Algae (BGA) from Soil

• Weigh approximately 10 g rice field soil and put it in 100 ml sterile water blank and mix thoroughly.
• Transfer 10 ml of the soil mixture to another flask containing 90 ml sterile water to make 10^-2 dilution.
• Prepare BG 11 medium and pour into a series of Petridishes. The chemical compositions of BG 11 medium are Sodium nitrate (1.5 g/L), Dipotassium hydrogen phosphate (0.031 g/L), Magnesium sulphate (0.036 g/L), Calcium chloride dihydrate (0.036 g/L), Sodium carbonate (0.020 g/L), Disodium magnesium EDTA (0.001 g/L), Citric acid (0.005 g/L) and Ferric ammonium citrate (0.006 g/L). Final pH after sterilization should be 7.1.
• Pipette out 1 ml of soil suspension from 10^-2 dilution over the BG 11 medium plates and spread it.
• Keep the plates in light chamber or partial sunlight and incubate for 3 - 4 weeks.
• Observe for the blue green colour growth on the agar surface of the BG 11 plates.

Mass multiplication of Blue Green Algae (BGA)

Mass multiplication of BGA in Trays

• Based on the natural ecology of these algae, a simple rural-oriented Open-Air Method of producing them in bulk has been developed.
• The basic principle is to grow them in natural sunlight under conditions stimulating these in the rice field.
• Shallow stays (15 cm × 7.5 cm × 22.5 cm) of galvanized iron sheet, or brick and mortar, or pits lined with polythene sheets are prepared. The size can be increased if more material is to be produced.
• About 10 kg soil is placed and mixed with 200 g Super phosphate.
• The trays are then filled with water (5 - 15 cm) depending upon the local conditions and rate of evaporation; the pH of the soil should be around neutral.
• After soil settles down, saw-dust and the starter culture are sprinkled on the surface of the standing water.
• The whole assembly is exposed to sunlight. In hot summer months, the growth of the algae will be rapid and in about a week a thick algal mat will be formed on the surface of the soil and sometimes even floats up. If the daily rate of evaporation is high, more water is added intermittently.
• When the algal growth becomes sufficiently thick, addition of water should be discontinued and the water is allowed to dry up in the sun.
• The dried algal flakes are collected from the surface and stored in bags for future use in the fields.
• The trays are again filled with water and a small amount of the dry algal flakes is added, as further inoculum. The process is continued as above.
• Once the soil in the tray is exhausted (usually 3 - 4 harvests), fresh soil is put and mixed with super phosphate and the process is repeated as before. To prevent the breeding of insects, application of Malathion (0.00075 ppm) or Carbofuran (3 % granules) is recommended.

Figure – 1: Mass multiplication of BGA in Trays

Mass multiplication of BGA under Rice field condition

• Select an area of 40 m² (20m x 2m) near a water source which is directly exposed to sunlight.
• Make a bund all around the plot to a height of 15 cm and give it a coating with mud to prevent loss of water due to percolation.
• Plot is well prepared and levelled uniformly and water is allowed to a depth of 5 - 7.5 cm and left to settle for 12 hrs.
• Apply 2 kg of super phosphate and 200 g lime to each plot uniformly over the area.
• The soil based composite starter culture of BGA containing 8 - 10 species @ 5 kg/plot is powdered well and broadcasted.
• Carbofuran @ 200 g is also applied to control soil insects occurring in BGA.
• Maintain the water level to a height of 5 cm.
• After 15 days of inoculation, the plots are allowed to dry up in the sun and the algal flakes are collected and stored.

Field Application of BGA in Rice field

• Blue Green Algae (BGA) are applied at the rate of 10 kg/ha over the standing water in the field one week after transplantation.
• The field is kept water logged at least for a couple of days immediately after algal application.

Beneficial effects of BGA

• Cyanobacteria have ability to carry out both Photosynthesis and Nitrogen fixation.
• Besides contributing to the nitrogen economy of the soils these algae have other beneficial effects like

a)     Good water holding capacity

b)  Ability to concentrate nutrients such as nitrogen, phosphorus, fixed carbon and trace elements

c)     Soil binding capacity

d)     Ability to scavenge sodium from salt affected soils are additional ecological advantages.

• The presence of BGA in the immediate vicinity of rice seeds can decrease Sulphide and Iron injury to the plants.
• Cyanobacteria also produce number of plant growth substances like Amino acids, Small proteins and peptides, Sugars, Complex polysaccharides, Vitamins and Growth hormones.
• A bulk of the organic matter produced by algal growth remains in the soil and becomes available to the next crop as organic enrichment.