BGA are a large and morphologically diverse group of phototrophic prokaryotes, which occur in almost every habitat on earth. This versatility may explain the remarkable lack of morphological (and presumably physiological) change seen in 3.5-billion-year-old fossilized cyanobacteria and their modern day counterparts (Adams, 2000).
Total energy required for the production of global ammonium fertilizers is equivalent to 2 million barrels of oil per day. 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.
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 use of algae as biofertilizer provides a cyclic nutrient-supply system with inherent ecological advantages.
Rice is one of the oldest cultivated crops and most staple food crop for more than a third of the world’s population. The inoculation of nitrogen fixing Blue Green Algae (BGA) is an alternative and sustainable source of nitrogen to increase the rice productivity. The mixed inoculum of Nostoc, Anabaena, Westiellopsis, Aulosira and Scytonema was used in field. The BGA inoculum with N: P: K (30:20:20 kg/ha) was found to be the most effective treatment for rice productivity as reported by Gurung, et.al. (2004); Paudel, et.al., ( 2012).
Biological nitrogen fixation is especially important in rice field and various other crops where Blue Green Algae (BGA) or cyanobacteria are recognized as significant contributors to the overall soil nutrient balance. Blue Green Algae find a highly favourable abode in the waterlogged conditions of Agriculture fields. BGA provide cheap nitrogen to plants besides increasing crop yield by making soil vital, fertile and productive. BGA as biofertilizer in rice popularly known as ‘Algalization’ helps in creating an environmentally safe agroecosystem that ensures economic viability in paddy cultivation and other various crops while saving energy intensive inputs.
A conservative estimate suggests that about two million hectares under rice are currently covered with algal biofertilizer technology. Earlier worker Roger et al. (1985) reported that algalization was adopted in only two states of India and there the inoculated fields comprise only a few percent of the total area under rice.
BGA are present abundantly in rice fields and are important in helping to maintain rice fields fertility through nitrogen fixation and involved in the photosynthesis. Ultrastructure of cyanobacterial cell wall, biochemical and pigment analysis of blue green algae were isolated from the paddy (Thamizh & Sivakumar, 2012).
A nitrogen-fixing strain of Gloeocapsa isolated from a rice-field was reported by Singh,et.al. (1986) to be highly resistant to the herbicides Machete and Basalin, whereas Nostoc muscorutn from another source was quite sensitive.
The agricultural importance of BGA in rice cultivation is directly related with the ability of certain forms to fix nitrogen. Contrary to heterotrophic N2-fixing bacteria, BGA represent a self supporting system capable of both photosynthesis and N2 fixation, the energy bill for both process being “paid by the sun”. Recent research, conducted mainly in India, has shown the feasibility of using BGA as a cheap additional nitrogen source for rice.
Various Institutes has taken a lead and developed BGA biofertilizer technology for farmers. The technologies for its rural production as well as commercial production are now available. Rao, et.al., (2004) considered the fact that 87% of the paddy area in India accounts for holdings of 1-4 hectares and 13% for holdings even less than one hectare; an inexpensive rural oriented ‘Algal Biofertilizer Technology for Rice’ was developed mainly for the well being of small and marginal farmers in India.
In India, considerable progress has been made in the development of BGA based biofertilizer technology.
It has also been demonstrated that this technology can be a powerful means of enriching the soil fertility and improving rice crop yields. However, the technology needs to be improved further for better exploitation under sustainable agriculture systems. It is important to obtain a much more detailed understanding of algal population dynamics over the whole annual cycle in agriculture systems. Extensive field studies aimed at developing region specific high quality inoculum are also needed. Understanding the biology of drought resistant algae may be useful in terms of extending this approach to dry crops.
The large-scale production of BGA bio-fertilizers also has an income generating potential and can be practiced as a profession. The technology for large-scale production of BGA biofertilizers with commercial dimensions involves indoor production to maintain round the year production schedules. Clay based BGA bio-fertilizers production technology has been developed for round the year production in a polyhouse under semi-controlled conditions.
On an average, BGA contribute 20-30 kg N/ha/season which means that chemical nitrogen fertilizer to that extent could be saved through these organisms. Application of BGA biofertilizer leads to increase in productivity of paddy by 10-15%. BGA improve soil health and maintain a continuous supply of crop nutrients and along with improves water holding capacity of soil and increases soil aggregation. BGA leads to population build up and enhances the microbial activity. Algalization induces early grain setting and maturity and checks weeds proliferation by blocking nutrient supply and light.
BGA is economical and easily adaptable by small and marginal farmers. BGA as biofertilizer is ecofriendly and non-polluting to the environment.
BGA are found to proliferate exuberantly in the different ecological niches of this region. The role of these organisms in the conservation of nitrogen level in the rice field ecosystem is considered to be of great economic significance. The contribution on this aspect has been made by Gunapati, et.al., (2010).
Watanabe et al. (1981); Grant et al., (1983) observations raise the possibility of deliberate manipulation of the ecosystem to favour blue-green algae by liming. phosphorus application, surface application of straw and grazer control.
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.
Kulik (1995) showed the beneficial effects of bio-fertilizers are addition of nitrogen, increased soil organic matter and soil aggregation. The role of bio-fertilizers in sustainable agriculture recorded special significance, particularly in the present context of high cost of chemical fertilizers has been made by Kannaiyan (2002). The production and application of bio-fertilizers to leguminous plants, oilseeds, rice, millets and forest nursery plants are very common in India as reported by many earlier workers. (Kannaiyan, 2002; Rai, et.al., 2004)
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