There is a continuous demand of agricultural products throughout the world, with the up surging human populations. Instead of using the synthetic fertilizers, growth promoters and other chemicals, the researchers are been constantly looking for an alternative to increase the crop yield and this is the reason that biofertilizers are much in demands as they ensures food safety and security.
Biofertilizers is the basic nutrient inputs of biological origin to support the sustainable plant growth. This is possible with the addition of the microbial inoculants as one of the primary source of biofertilizers. Therefore, we can say that ‘biofertilizers are the substances that contains the varieties of microbes, and has the potential to enhance the plant nutrient uptake by increasing the accessibility for the plant root hairs to absorb’.
Biofertilizers are environment-friendly, cost effective, easily accessible and most promising alternatives for the hazardous synthetic fertilizers. Even these (biofertilizers) have different categories, such as:
- Symbiotic nitrogen fixers.
- Asymbiotic nitrogen fixers.
- Phosphate solubilizing bacteria.
- Organic fertilizers.
Few significant features of the above the mentioned biofertilizers are been discussed further along with the few more points.
Symbiotic Nitrogen Fixers
One such example of the symbiotic nitrogen fixers are the diazotrophic microorganisms, they serve as the biofertilizers. The Bradyrhizobium sp. and Rhizobium sp. are the known examples, which are still under research to get them genetically modified in such a way that they can be prove more useful for nitrogen fixation.
One of the common practice observed in countries like India is the green manuring since long time. In this type of farming practice the leguminous plants are benefitted by the symbiotic nitrogen fixing bacteria that are been ploughed into the soil along with the non-leguminous plants also.
Therefore, the fixed nitrogen are more advantageous for the non-leguminous plants and this method is considered to be the natural and most beneficial one for the plants to use the available nitrogen and it also reduce the use of chemicals fertilizers. The Rhizobium sp. can fix the 50-150 kg nitrogen/hectare/annum.
Asymbiotic Nitrogen Fixers
The asymbiotic nitrogen-fixing bacteria are known for fixing the nitrgoen directly to nitrogen-rich compound from the available gaseous nitrogen. One such example is the Azospirillum sp. and Azobacter sp., where even after the death of these microogansisms, they serve the soil by enriching with the nitrogenous compounds and act as the biofertilizers.
Blue-green algae (Cyanobacteria)
Blue-green algae are known for fixing the nitrogen in the from of organic compounds such as amino acids, proteins. The cyanobacteria can multiply in the water logging conditions, and here for the getting the nitrogen we use the term ‘algalization‘ where the cultivation of blue-green algae is done in the field that can serve as the source for biofertilizers.
Additionally, apart from fixing nitrogen, the other reasons for cultivating the blue-green algae is the accumulation of biomass that enhances the physical properties of the soil. This is helpful in restoring the alkaline soils along with the partial tolerance to the pesticides. Cyanobacteria are useful in paddy fields and the common examples includes the Azospirillum sp. and the Azobater sp.
Azolla is the type of aquatic fern, containing endophytic cyanobacterium ‘Anabena azollae‘ in the leaf cavities. Here, it has been observed that Azolla along with Anabaena are helpful in fixing nitrogen and serve as biofertilizers, but has few limitations and is not much in use. These limitations includes; firstly, the Azolla plant requires plenty of water to grow.
Secondly, the cultivation of Azolla is labor intensive. Lastly, the plant get easily damaged by the pest disease or any such infections.
Phosphate Solubilizing Bacteria
There are certain bacteria’s that have the potential to convert the non-available inorganic phosphorus found in soil into the utilizable form of phosphate (organic or inorganic), for example bacillus, thiobacillus. These bacteria are also capable of producing siderophores, that can chelates with the iron and make it unavailable to harmful bacteria.
So, apart from producing phosphate, these bacteria also protect the plants from the disease causing agents (bacteria).
Mycorrhizas have the fungal roots, for example ‘Glomus sp.’ have different morphological structure. This development is due to the mutual symbiosis between plant roots and the root-inhabiting fungi. The growth of Mycorrhizas are seen in such plants (herbs, shrubs or trees), where the individual plants have the limitations with nutrient supply.
The development of mycorrhizas depends on the growth of the fungus, if it on the surface of the roots of a plants it is known as ectomycorrhizas, while if it is inside the roots it is known as endomycorrhizas.
In the recent years, the artificially produced inoculum of the mycorrhizal fungi is used to improve the crop yield. This has resulted in the plants growth, along with improvement in the crop yield and resistance against the pathogens (biotic) and climatic conditions (abiotic) and stress.
The useful fertilizers can be the several organic wastes, that includes urine, animals garbage, crop residues, oil cakes, animal dung, sewage crops, etc., still it is seen that the maximum amount of the organic wastes remains unused as the organic fertilizers. These organic wastes can turn into the useful organic manures if used properly.
Benefits of Biofertilizers
- Fertility of the soil gets increased with time, after using the biofertilizers.
- Biofertilizers are free from the environmental pollution.
- Cost effective, can be easily produced. Poor and small farmers are benefitted.
- With the biofertilizers the quality of the soil, like texture, water-holding capacity gets increased.
- Apart from supplying the nutrients to the soil, biofertilizers also enhance the plant growth by producing plant growth hormones, disease resistance properties and antibiotics.
- The tolerance against the heavy and toxic metals gets increased, with the use of biofertilizers.
- Redemption of alkaline or saline soil can be done by using biofertilizers.
- The crop yield can be improved and they (plants) become more tolerable against the biotic and and abiotic stresses.
Limitations of Biofertilizers
- Hard to get the spectacular results like in the case of synthetic fertilizers.
- Biofertilizers are unable to meet the demand of the increasing nutrient supply of plants to grow.
Biofertilizers can bring the revolutionary changes in the field of agriculture as these are easily available, eco-friendly and are of low cost. Even they can be of use in meeting the increasing demand of crops and other agricultural products and the future generations can also protected with the conserving and sustainable natural resources used in the farming. Thus, there is a need of proper awareness among the farmers and to guide them for the proper use of biofertilizers.