Poor soil fertility is a major limiting factor to crop yield; which is worse in the case of resource – poor farmers in developing countries. Along with the existing poor fertility, the continuous degradation of soil quality due to, the haphazard use of chemicals has made the situation worst. During the initial stages of chemical fertilizers use, they were highly accepted by the farmers as they were promised as, capable of giving increased crop production; but, with time, the evil sides of chemical fertilizers were being exposed to the world. Chemical fertilizers pollute the air, water, and soil; which results in an unhealthy environment and in a damaged biosphere. These chemicals not only affect animals, but also they reach in to the food chains with their toxicity and create many complicated and fatal diseases to the human body.
A Potential Solution
These days people are more conscious about the danger of chemical fertilizers than any time before. But with the limitation of feeding billions of mouths, it is not an easy task to simply kick away chemical fertilizers until the required crop production is secured with other suitable alternatives. A number of leading scientists across the world started searching for that desired alternative and found ‘Biofertilizers’ as a great one which can give a good crop production on one hand and possess no potential danger to the environment and human health on the other.
Biofertilizers have come to the center of interest to many scientists and agronomists because of some vital issues to deal with such as maintaining soil health, checking environmental pollution, cutting down the use chemicals for crop production etc. Biofertilizers are the cheap, eco-friendly and renewable substances those contain selected strains of beneficial soil microorganisms which supply adequate quantity of nutrients to the host plants to ensure their proper growth and physiological regulation.
“Biofertilizers are products containing living cells of different types of microorganisms which when, applied to seed, plant surface or soil, colonize the rhizosphere or the interior of the plant and promotes growth by converting nutritionally important elements (nitrogen, phosphorus) from unavailable to available form through biological process such as nitrogen fixation and solubilization of rock phosphate.” (Rokhzadi et al., 2008).
How do Biofertilizers Work
Biofertilizers are effective in supplying many nutrients to the soils in ways that are eco-friendly and highly balanced. Biofertilizers trap atmospheric nitrogen to the soil and convert them into plant usable forms. They also convert the insoluble phosphate forms into plant available forms. They stimulate root growth by producing some hormones and antimetabolites. These fertilizers also rebalance the fertility status of a soil and thus stimulate soil life. Application of biofertilizers boosts nutrient cycling in the soil and starts ‘biological buffering’ to ameliorate the existing stresses in the soil. The microbes added to the soil as biofertilizers can stimulate the host immunity and protect the crops from pests and diseases; thus, they can help reducing the use of pesticides to a great extent.
Some Special Advantages of Biofertilizers
Biofertilizers have some special benefits-
• Biofertilizers have longer shelf life.
• Farmers can use biofertilizers quite easily.
• Biofertilizers are completely free of contamination.
• They have a greater capacity to fight with the native population.
• They are not expensive but serve better.
• They bring high commercial revenues.
Types of Biofertilizers
Nitrogen Fixing Biofertilizers
Nitrogen fixing biofertilizers contain many microbial inoculants or group of microorganisms which are capable of converting atmospheric N2 into organic compounds and eventually into plant usable forms. Thus, these biofertilizers fix N2 from the atmosphere and supply that to plants in usable forms which ultimately increase soil N2 level and overall soil fertility level. A number of microorganisms are used as Nitrogen fixing biofertilizers. For instance Azotobacter, Anabaena, Nostoc, Clostridium etc. are used as free-living N2 fixing biofertilizers; while Frankia, Rhizobium, and Anabaena azollae are used as symbiotic N2 fixing biofertilizers and Azospirillum is used as associative symbiotic N2 fixing biofertilizer.
Phosphorus Solubilizing Biofertilizers
These biofertilizers solubilize the insoluble phosphates from various phosphate sources and make them plant usable. They lower soil pH by secreting organic acids and thus dissolve the bound phosphates. Some bacteria used as P-solubilizing biofertilizer are-Bacillus megatherium, Pseudomonas striata, Bacillus circulans, Bacillus subtilis; and some fungus used for this purpose are — Aspergillusawamori and Penicilliumspp.
Phosphorus Mobilizing Biofertilizers
Different fungi and mycorrhiza, which stimulate the transfer of P ions and thus metabolic processes, belong to this group. Microorganisms those are used as P mobilizing biofertilizers are-Glomus spp., Gigaspora spp., Boletus sp., Laccaria spp., Pisolithus sp., Rhizoctoniasolani, Pezizellaericae etc.
Biofertilizers for Micro Nutrients
The microbes used here are silicate and zinc solubilizer bacterial species. These microbes also degrade silicates and aluminum silicates. Bacillus spp. is an example of this group.
Plant Growth Promoting Rhizobacteria
These microbes act as biofertilizers as they stimulate plant growth by improving nutrient availability. They are also effective as biopesticides and bioprotectants. Pseudomonas sp., and Bacillus sp. belong to this group.
How to Make Biofertilizers
Producing biofertilizers is a job requires great care. Generally making biofertilizer consists of 6 major steps. They are-
• Choosing active organisms is the first step of making biofertilizers. You must decide which type you prefer from nitrogen-fixing bacteria, organic acid bacteria, and a combination of some other organisms.
• Isolation and selection of target microbes are the second step where the target microbes are separated from their habitation. Generally, the microbes are isolated from plants root or by luring them with a decoy.
• Selection of method and carrier material is the next step of biofertilizer preparation where the isolated organisms are grown on a petri plate, shake flask, and then glasshouse to choose the right one. Along with the selection of right method, selection of right carrier material is also equally important.
• Selection of propagation method is the fourth step of biofertilizer making process. It refers to finding out the optimum condition for the organisms.
• The next step is making and testing prototype.
• The final step is large scale testing, where the fertilizer is widely tested under different environmental conditions to analyze its performance under various conditions.
How to Apply Biofertilizers
• For main field application, 1 kg of inoculants is sufficient for a field of 1 acre. That amount of inoculants is mixed with 20 kg of powdered farm yard manure and then broadcasted on the land. Biofertilizers are applied to the main field just before transplanting a crop.
• For transplanted crops, the roots of the seedlings are dipped in a mixture containing inoculants. Around 400g of inoculants is added to 40 liters of water to prepare the mixture in an amount sufficient for the seedlings to be planted on a 1-acre land. Seedlings required for a 1-acre land are taken and their roots are dipped into the mixture for 5-10 minutes before transplanting them.
• Biofertilizers are also used for seed treatment after making a slurry with them. 200g of inoculants and 200 ml of rice kanji are mixed together to make the slurry in sufficient amount for a 1-acre land. A uniform coating of inoculants are created over the seeds by treating them with the slurry and then shade drying them for 30 minutes. After shade drying, the seeds need to be sown within 24 hours.
How to Store
• The packets containing biofertilizers must be kept in a cool place which is protected from heat and direct sunlight.
• Room temperature or cold storage condition, any of these two can be used in storing inoculants packed in poly bags or gunny bags.
• The inoculant population in the inoculant containing packets should be checked after each 15 days, as a minimum number of cells must be present per gram of inoculants to keep the fertilizer effective.
Rokhzadi A., Asgharzadeh A., Darvish F., Nourmohammadi G. and Majidi E. 2008. Influence of plant growth-promoting rhizobacteria on dry matter accumulation and yield of chickpea (Cicer arietinum L.) under field condition. Am-Euras. J. Agric. Environ. Sci. 3(2): 253-257.