The worldwide spread of inflation, initiated by several fold rises in Petroleum price thereby depicting its striking influence on the prices of chemical nitrogenous fertilizers, the prices of nitrogenous fertilizers have nearly doubled during the last 3-4 years. This has necessitated to search for cheaper source of nitrogen to meet the needs of crops. This has rejuvenation of soil microbiology to tap out the biological fixation of nitrogen.
Soil is a natural habitat of variety of agriculturally beneficial microorganisms. Certain soil microorganisms have an ability to absorb and convert atmospheric nitrogen to the readily available form to the plants. Whereas certain soil microorganisms solubalized part of the bound phosphates of the soil and thereby make them available to the plants. Both these attributes make them important to be used as Biofertilizers. Biofertilizers, unlike synthetic fertilizers, are of natural (microbial) origin, have a wide range of applicability, & leave no toxic or non-biodegradable residues. They are thus gradually replacing synthetic fertilizers in several applications.
Biofertilizers are manufactured by fermentation of a complex heterogeneous medium using commercially viable microbial cultures. Two types of biofertilizer formulations are popular - carrier-based formulations & liquid formulations.
Biofertilizer is most commonly referred to the use of soil microorganism to increase the availability and uptake of mineral nutrient for plant .So it is necessary to define the term biofertilizer. There is proposal that biofertilizer be defined as a substance which contain living microorganism which colonizes the biosphere or the interior of the plant and promote the growth by increasing the supply or availability of primary nutrient or growth stimulus to the target crop , when applied to seed plants surface or soil.
The relevance of biofertilizers is increasing rapidly since chemical fertilizers:
(i) utilize petroleum (nitrogenous fertilizers),
(ii) are costly,
(iii) are short in supply, and
(iv) damage the environment, e.g., about 10% of the ground water samples in Punjab contained more NO3- than the maximum permissible limit prescribed by World Health Organization.
In contrast, biofertilizers are:
(i) low cost inputs,
(ii) lead to soil, enrichment and
(iii) are compatible with long term sustainability and
(iv) are ecofriendly and pose no danger to the environment.
However, the acceptability of biofertilizers has been rather low chiefly because they do not produce quick and spectacular responses.
In addition, the amount of nutrients provided by them is not enough to adequately meet the total needs of crops for high yields. Therefore, a pragmatic approach more likely to succeed will be to develop a rational and effective combination of biofertilizers and conventional fertilizers for optimum crop yields.
A group of free-living nitrogen fixers are ‘cyanobacteria’ commonly called the ‘Blue-green algae’ (BGA). More than a hundred species of BGA can fix nitrogen.
Nitrogen fixation takes place in specialised cells called the ‘Heterocysts’ (large, thick walled and metabolically inactive cells) which depend on vegetative cells for energy to fix nitrogen while the fixed nitrogen is utilised by the vegetative cells for growth and development. BGA are very common in the rice fields (the micro-aerophilic condition and alkalinity are conducive to the algal population).
If no chemical fertilisers are added, inoculation of the algae can result in 10-14 % increase in crop yields. Unlike Azotobacter, the BGA are not inhibited by the presence of chemical fertilisers.
Here, live cells of bacteria are used as fertilisers. They are the principal nitrogen fixers in the soil and may be either free-living or symbiotic (within the nodules of legume roots, leaf nodules of certain plants and stem nodules of Sesbania grandiflora). Some bacterial genera can solubalize phosphorus from the bound form (Bacillus, Pseudomonas sp.).
There are certain other bacterial members which during their metabolic activity, make available certain essential trace elements like manganese, calcium and zinc in the soil for plant absorption. Some bacteria like Agrobacterium sp. and Pseudomonas fluorescence supply growth hormones like Indole acetic acid to the plants.
Certain groups of bacteria like the Pseudomonas fluorescence living in association with the rhizosphere of most of crop plants (rhizobacteria promoting plant growth) supply all the essential nutrients required for the growth of the crop and in addition, protects the plant roots from the attack by soil-borne pathogens (saprophytic suppression) heads.
Biofertilizers thus include the following:
(i) Symbiotic nitrogen fixers Rhizobium spp.;
(ii) Asymbiotic free nitrogen fixers (Azotobacter, Azospirillum, etc.);
(iii) Algae biofertilizers (blue green algae or BGA in association with Azolla);
(iv) Phosphate solubilising bacteria;
(v) Mycorrhizae;
(vi) Organic fertilizers.
The need for the use of biofertilizers has arisen, primarily for two reasons. First, because increase in the use of fertilizers leads to increased crop productivity, second, because increased usage of chemical fertilizer leads to damage in soil texture and raises other environmental problems. Therefore, the use of biofertilizers is both economical and environment friendly. The pragmatic approach will be to develop the integrated nutrient supply system involving a combination of the use of chemical fertilizers and biofertilizers. India is not self sufficient in fertilizer production.
Among the large number of free-living nitrogen fixers, only two have attracted the scientists, they are Azotobacter and Klebsiella. Azotobacter requires oxygen to flourish and Klebsiella and Rhodospirillum can survive both in the presence and absence of oxygen. Apart from fixing nitrogen, Azotobacter chroococcum has the ability to synthesise and secrete B-vitamins, growth hormones and antifungal antibiotics into its environment. Azotobacter has one drawback; its nitrogen fixing ability is regulated by the presence of nitrogenous compounds in its environment.
Vesicular Arbuscular Mycorrhiza (VAM) is the most abundant kind of mycorrhiza described as ‘a universal plant symbiosis’. They are found in practically every taxonomic group of plants and the list of species not infected is probably far shorter than the infected ones. Lack of host specificity is even more characteristic of this symbiosis than other types known. Studies on VAM fungi conducted during last few decades envisaged their occurrence in a wide variety of hosts, different habitats and variability in quality and quantity.
An estimated capital investment of Rs. 7,000 crores was needed by the end of Seventh Five Year Plan period to achieve self sufficiency. Realizing the importance of biofertilizers in possible to introduce these genes into non is hoped supplementing the use of chemical fertilizers, the Government of India had launched the 'National Project on Development and use of Biofertilizers’ during the Sixth Five Year Plan.
Atmosphere contains 78% nitrogen which is a very important nutrient for plant growth. Azotobactor fixes the atmospheric nitrogen in the soil and make it available to the plants. It protects the roots from other pathogens present in the soil.
Azotobacter spp: These are free living bacteria which grow well on a nitrogen free medium. These bacteria utilize atmospheric nitrogen gas for their cell protein synthesis. This cell protein is then mineralised in soil after the death of Azotobacter cells thereby contributing towards the nitrogen availability of the crop plants.
ARTICLE BY,
Rudra Sharan Dwivedi
M.Sc Biotech.
Company: RMS Regrow
rudsd1987@gmail.com
.png)
