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Explora: Environment
and Resource Anabaena-Azolla for crops and bioenergy

Rhizobium, Azotobacter, Azospirillum, cyanobacteria, of crop is produced with nitrogen fertilization or 400 kg/
Arbuscular Mycorrhizae, etc. Using biofertilizers is ha without it. The ability of modern rice varieties to yield,
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important because they enrich the soil with a variety of in addition to the rising costs of nitrogen fertilizers, is
micro- and macro-nutrients and facilitate the release partly due to the significant amounts of fossil fuel energy
of substances that regulate plant growth, biodegrade required to produce them. Therefore, the development
organic matter, synthesize antimicrobial compounds, and of alternative, affordable nitrogen sources has become
support other beneficial processes. The advantage of using essential. Naturally occurring nitrogen resources, such
biofertilizers is that they improve soil structure without as those provided by Azolla, have the unique capacity to
harming any organisms in the food chain. 62 fix a significant portion of N in the soil for agricultural
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use through biological means. The rice field ecosystem
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Rice is the staple diet of many people in Asia. As the
population grows, so will the demand for food. The is generally divided into three main ecological layers:
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Aerobic, anaerobic, and rhizosphere zones. The floodwater
use of cyanobacterial fertilizers, such as green manure, and soil surface are sites of aerobic phototrophic nitrogen
specifically A. azollae, has improved crop yields in rice fixation by free-living cyanobacteria and the symbiotic
fields not only in India but also in China, Egypt, Japan, Azolla-Anabaena N -fixing complex. The anaerobic lower
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the Philippines, and other tropical rice-growing nations. layers serve as sites for heterotrophic nitrogen fixation.
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Chemical nitrogen fertilizers have long-lasting negative In addition, the rhizosphere is a primary location for
effects on both the soil and the environment. As a result, nitrogen-fixing. 1
the soil may become infertile, and farmland may become
overnourished. Without harming or contaminating Cyanobacteria release fixed nitrogen for plant use
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the environment, using Azolla as a biofertilizer is an through exudation or microbial breakdown after cell
effective way to increase rice harvest production by 20 – death. This nitrogen is mainly released as polypeptides,
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30%. Anabaena–Azolla also provides a natural source of with smaller amounts of free amino acids, vitamins,
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many nutrients, especially nitrogen, which supports plant and auxin-like compounds. In the rice field, some of
growth. Moreover, Azolla-Anabaena helps maintain the converted nitrogen becomes available to the plants,
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the optimal soil pH for rice growth while increasing soil whereas the remainder is returned to the surrounding
nutrients, organic matter, and the efficiency of inorganic soil. A large amount of nitrogen (between 75% and 80%
fertilizers. 2,64 of the total fixed) is released during the decomposition of
Azolla biomass into the paddy soil, where it is absorbed by
6.1. Role of Azolla in rice field plants. 50
No plant species can utilize dinitrogen; hence, plants The following outcomes result from the extensive use
must obtain nitrogen in other forms for growth, often of Azolla as a suitable biofertilizer in rice fields: up to
through prokaryotic symbiotic microbes such as bacteria 40 – 60 kg of nitrogen/ha of rice crop, with an increase
and cyanobacteria. 34,36,65,66 Under optimum conditions, in nitrogen content within a matter of weeks. The use
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the cyanobiont can fix a considerable amount of nitrogen, of Azolla biofertilizer boosted crop nitrogen recovery by
releasing around 70% of the fixed nitrogen to surrounding 49 – 64% and reduced nitrogen loss by 26 – 48%. After
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crops. One such natural micro-ecosystem is the symbiosis transplanting, rice was given 300 kg/ha of inoculated
of Azolla and A. azollae, where the cyanobacteria inhabit Azolla, which boosted rice production comparable to
the mature leaves of the plant. The cells differentiate into the application of 100 kg/ha of urea. Azolla increases
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heterocysts, where the process of nitrogen fixation takes the amount of organic matter in the soil, makes other
place. Once Azolla decomposes, the nitrogen it fixed is macronutrients more readily available, decreases NH
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released, along with other nutrients such as potassium, volatilization, and is essential for the control of weeds.
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phosphorus, Fe, zinc, Mo, and sulfur into the environment, The application of Azolla as green manure to wet soil
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hence making it an effective biofertilizer. The high rate accelerated soil mineralization, releasing 60 – 80% of
of nitrogen fixation by Azolla is due to the presence of the nitrogen within 2 weeks. Instead of using alternative
cyanobionts in its leaf cavities. The application of Azolla nitrogen fertilizers, farmers can manage between 30 and
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as a biofertilizer in paddy fields provides around 40 – 60 kg 60 kg of nitrogen by adding Azolla to rice crops at a rate of
nitrogen/ha per crop. 37 16,000 kg/ha, improving the sustainability of soil health.
The primary rate-limiting factor in rice production is Azolla injection reduces NH volatilization by 12 – 42% in
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the availability of nitrogen. 63,68 The overhead labor costs flooded water. 63
associated with tillage, irrigation, water control, and other Soil enzyme activity is recognized as an indicator of
agricultural processes are the same whether 2,000 kg/ha soil fertility, microbial activity, and nitrogen supply. The
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Volume 2 Issue 2 (2025) 7 doi: 10.36922/eer.7975