Bio fertilizers : Use and importance

Nitin Kumar Pandey *

Indian economy is based on agriculture. Agriculture plays a vital role in Indian GDP Indian agriculture has seen major technological advances since late 1960s and has succeeded in enhancing food production and in achieving self-sufficiency.

The introduction of high yielding varieties of seed and the increased use of fertilizers and irrigation followed by the pest control measure in a later parts lead to green revolution in Indian agriculture.

The total fertilizers requirements in India would be 24 million tones, and against the present consumption level of 14 million tones. Which is beyond any single type of nutrient source to accept the challenge of appropriate nutrient supply. Integrated use of all the sources such as mineral, fertilizers, organic manures, biofertilizers etc. are the only alternate for improving soil fertility.

India is fourth largest user of chemical fertilizers in the world. The strategy for sustaining satisfactory yield levels envisage nutrient balance and efficient nutrient cycling. This can be achieved through integrated use of mineral, fertilizers, compost, organic manures, green manure, and biological inoculants etc.

However, such indiscriminate use of chemical fertilizers also led to environmental pollution, erosion of soil quality and contamination of farm produce and ground water by chemical fertilizers residues and consequent health hazards.

Chemical fertilizers have affected the environment through nitrate poisoning and experimentation of beneficial micro flora and micro fauna by adversely affecting the physical and chemical structure of the soil.

It has been observed that the concentration of chemicals in ground water has reached levels, which are hazardous to human, and live stock population. Post green revolution has experienced continuous decline in food grain production against consumption of NPK. The NPK consumption in India is above the world average consumption, however the average yield per hectare is much below the world average.

The term bio fertilizers or which can be more appropriately called ‘microbial inoculants’ can be generally defined as a preparation containing live or latent cells of efficient strains of nitrogen fixing, Phosphate solubilizing or cellulytic microorganisms used for application of seed, soil or composting areas with the objective of increasing the number of such microorganisms and accelerated certain microbial process to argument the extent of the availability of nutrients in a form which can be easily assimilated by plant.

In large sense, the term may be used to include all organic resource for plant growth, which are rendered in an available form for plant absorption through micro organisms or plant associations. The potentials of biofertilizers for promoting sustainable agriculture have been known for many years. “Microbial inoculants” or culture is the most appropriate name of biofertilizers.

Important microorganisms used as biofertilizers-

Blue Green Algae (BGA)- It is most common species are Anabaena and Nostoc. It can be grow in temperature range of 25 to 450C. Standing water of 2-10 cm in the field is prerequisite for its growth. It fix about 20-45 kg nitrogen per hectare. It grow well in pH 7-8 and soil high in organic matter.

Rhizobium- This is a soil bacterium that fix nitrogen after becoming established inside root nodules of legumes characterized by their unique ability to infect root hairs of legumes and induce effective N2-fixing nodules to form on the roots.

They are rod shaped living plants which exist only in the vegetative growth stage. Unlike many other soil microorganisms’ rhizobia produce no spores and they are aerobic and motile. Symbiotically it fix nitrogen 50-100 kg/ha with legumes like chickpea red gram, pea, lentil, green gram, etc. Oil seed legumes like soya bean and ground nut and forage legumes like berseem and Lucerne.

Azotobacter- Azotobacter is free living aerobic nitrogen-fixing bacteria, which can substitute part of inorganic fertilizers. It saves nitrogenous fertilizers by 10 to 20 per cent. Apart from its ability to produce antifungal antibiotics and fungistatic compounds against pathogens like fusarium, Alternaria and Trichoderma. Vegetable crops in general respond better to azotobacter inoculation than other crops.

Azolla- It is a small aquatic fern with a branched stem and bi-lobed leaves having association with Anabaena that fixes atmospheric nitrogen. When it dies and decays in the soil, nitrogen becomes available to the plant. It contains 45 per cent nitrogen, 2.6 per cent phosphorus and 0.9 percent potash and fixes about 30-40 kg nitrogen per hectare. It survives well in temperature range of 20 to 300C and suitable with 5.5 to 7.5 pH of soil. Azolla can double its body weight in 3.5 days. Azollapinnata is the common species.

Azospirillum- azolla are a group of bacteria found in association with the root system of many vegetable crop plants. It is a type of symbiosis where the bacterial cells are found colonizing the root cortical cell or the intercellular space in the cortex. These bacteria grow better under reduced oxygen levels.

It increases the yield mainly due to release of growth promoting substances and protection from disease than from the contribution of nitrogen fixation. Fix nitrogen from 10-40 kg per hectare. Azospirillum inoculation helps the plants in better vegetative growth and also save nitrogenous fertilizer up to 25-30 percent.

Its effect is well pronounced in summer under irrigated conditions, where the optimum temperature of 32-350C is available for good growth. It is mainly used for oil seeds.

Mycorrhizal Fungi- It is the most common fungal association among angiosperms. It is prepared by fungifunji belonging to the genera, Gigaspora, Glomus etc. The VAM (Vesicular Arbuscular Mycorrhiza) fungi makes more nutrients available to the plants. It is also helpful in the biological control of root pathogens.

Mycorrhiza increases capacity of the root absorbing surface and reaches outside the root depletion zones. It directly translocates nutrients like zinc, phosphorus, copper, potassium Aluminium, Magnesium from the soil to the root.

Phosphate Solubilizing Microorganisms (PSM)- PSM are one of the most important elements required for plant growth and yield. Pseudomonas, Bacillus produce organic acid and enzymes like acid phosphatases and phytases to solubilize insoluble inorganic phosphate compounds such as di-calcium phosphate, tri-calcium phosphate hydroxyapatite and rock phosphate.

Many species of penicillium are capable of production of organic acids like fumaric, gluconic, citric, oxalic acids which may dissolve insoluble phosphate of the soil.

Application method of Biofertilizer

Biofertilizer is used in three ways for example,

1. Soil Application- It is very useful for control to soil prove pathogens. 500 ml phosphorus soluble mycorrhiza is sufficient for one hectare. 1200-1300 kg FYM mix with 500 ml PSM and have to keep under tree shade for 12 hrs and spraying water to maintain moisture. Then use the mixture as soil application after last ploughing. They are very effective bio fertilizers for plant growth.

2. Root Treatment- It is required for transplanting crops for example paddy and vegetable nursery. PSM/Azospirillum is used for treatment of vegetable and paddy crops. The required quantity of PSM or azospirillum mixed with 10-15 litres of water in a cane and roots of seedlings has to be dipped for a minimum half hour before transplanting. It is effective and economic for farmers.

3. Seed Treatment- It is a very important method used for healthy seedling and crops. The seed treatment is benefitted and effective for farmers. Seed treatment with azotobacter, Azospirillum, Rhizobium along with PSM can be done. The seed treatment can be done with any of two or moe bacteria. There is no side and antagonistic effect.

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