|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|Indian experience with algal ponds|
The ability of certain forms of blue-green algae to carry out both photosynthesis and nitrogen fixation confers on them an ecological and agricultural advantage as a renewable natural resource of biological nitrogen. Nitrogen is one of the most important crop nutrients, and the great demand for nitrogenous fertilizers is apparent from the more than 580 chemical fertilizer plants now in operation or under construction throughout the world, representing an investment of over US$10,000 million.
It is estimated that the total energy required for the production of global ammonium fertilizers is equivalent to 2 million barrels of oil per day - a non-renewable resource. The energy crisis has driven fertilizer prices unrealistically high, dramatically illustrating the dependence of the world's food crops on petroleum-based fertilizers. Hardest hit by the chemical scarcity are the densely populated and land-scarce nations of Asia, where more than half of the earth's people live. Most depend on rice as their staple food. The millions of small-scale rural farmers in this region who have reaped the benefits of the new rice technology often lack the capital for chemical fertilizers. Any saving in the consumption of this fertilizer without affecting productivity, and the introduction of a cyclic nutrient supply system through biological sources, will be ecologically and economically advantageous.
Recent research has clearly shown that one of the most effective nitrogen-fixing biological systems in the rice fields are certain blue-green algae that, expressed on a per ha basis, contribute about 25 - 30 kg N/ha/season. A rural-oriented device to exploit these algae has been developed at the Indian Agricultural Research Institute at New Delhi. The merit of this process lies in its adaptability by the individual farmer without any appreciable capital investment or technical complications. Many farmers are now using this method to produce their own algal inocula for field application.
The basic principle is to grow algae using natural sunlight under conditions simulating the rice field. A thin, one-inch layer of soil is spread in rectangular trays or shallow dugout areas lined with polyethylene and flooded with two inches of water. After the soil settles down, the desired strains of blue-green algae are inoculated into these with a little superphosphate. The entire unit is kept exposed to the sun, and within a week, the entire water surface is covered by a copious growth of the inoculated species of algae. The standing water and its algae crop are allowed to dry in the sun, and the dried algal flakes are collected for field use. During bright summer, a continuous production of about 100 kg algal material is possible every fifteen days from an area of about 25 m² The cost of production is about 12 cents/kg, and the farmer needs only about 10 kg/ha to give him about 25 - 30 kg N/ha. The inherent capacity of these algae to stand extreme dessication has made it possible to preserve the product in a sun-dried form without any impairment of its viability (5, 6).
In India, a significant portion of algae production appears to have great potential as a highprotein feed supplement for livestock, particularly for poultry, and also will make an excellent biofertilizer for rice. This, coupled with the emphasis on waste recovery and efficient land utilization, will encourage the integration of algae-feed-fertilizer production with livestock raising in the nitrogen recycling systems. The major merit of algae as animal feed is that low-quality algal protein can be converted by the animals into higher quality protein in the form of meat or meat byproducts without the necessity for extensive pre-processing of the algal product. The use of algae as biofertilizer provides a cyclic nutrient-supply system with inherent ecological advantages.