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Sustainable crop production depends much on good soil health. Soil health maintenance warrants optimum combination of organic and inorganic components of the soil. Repeated use of chemical fertilizers destroys soil biota. In nature, there are a number of useful soil microorganisms, which can help plants to absorb nutrients. Their utility can be enhanced with human intervention by selecting efficient organisms, culturing them and adding them to soils directly or through seeds. The cultured microorganisms packed in some carrier material for easy application in the field are called bio-fertilisers.

Bio-fertilisers are living microorganisms of bacterial, fungal and algal origin. Their mode of action differs and can be applied alone or in combination. By systematic research, efficient strains are identified to suit to given soil and climatic conditions. Such strains have to be mass multiplied in laboratory and distributed to farmers. They are packed in carrier materials like peat, lignite powder in such a way that they will have sufficient life.

Biofertiliser is perhaps the most potential solution of the agricultural pollution today. The land loosing fertility to excessive use of chemicals may get replenished through the use of biofertilisers. It enhances the nutrient availability to cropping plants (by processes like atmosphere N-fixing or dissolving P present in the soil); and also imparts better health to plants and soil thereby enhancing crop yields in a moderate way. As the mode of action of biofertilisers follow natural course of actions, these generally, do not render any problems of enhanced salinity, acidity or alkalinity, high rate of soil erosion etc.

In the vast areas of low input agriculture and oil seeds production, as also in crops like sugarcane, etc. these products are of much use to give sustainable production. In view of the priority for the promotion of organic farming and reduction of chemical residues in the environment, special focus has to be given for the production of biofertilisers.

Microorganisms that play crucial role in the fertility management are either free living or having symbiotic association with plants. Based on the type of micro-organisms, biofertilizers are classified as follows:

The benefits of biofertiliser use are not as visible as that of chemical fertilizers. Therefore, the results are not dramatic and till date many farmers are not aware of the significance, excepting in States like Maharashtra, Gujarat, parts of Karnataka and Tamil Nadu. In fact in many states, the biofertiliser use being is promoted and supported by the State Governments. In those cases, the biofertilisers are mainly purchased by State Agriculture Departments and distributed to the farmers at concessional rates. About 200 to 500 grams of the carrier material is only needed per acre, costing about Rs.10/- to 25/. But the production system of biofertilisers in India needs more attention for lending an overall support to the farmers. It had been estimated that the presently possible production of about 7500 to 9000 TPA was far below the potential requirement of 7.6 lakh TPA in the year 2000-2001 as estimated by the National Biofertiliser Development Centre (NBDC) Ghaziabad.

[This estimated demand of NBDC was based on the cultivated area of the country and treatment of the total seed sown at the rate of 200g biofertiliser per 10 kg of seed. Although this assumption reflects only the macro level requirement, even if 50% of the cultivated area is to be brought under biofertiliser application, there will be a wide gap between the actual production and the requirements.]

The current trends indicate that there is a steady increase in the demand in the Southern states except Andhra Pradesh, Western States and Madya Pradesh and Rajasthan. In the context of increasing awareness about the use of natural products and organic agriculture, these products will have good scope.

Most of the cultivated tropical and subtropical soils have good population of index of establishment of an efficient nitrogen fixing system. Competitive and efficient strains of Rhizobium used for inoculation will ensure maximum nitrogen fixation. Absence of effective Rhizobium strains is responsible for poor nodulation encountered in many areas. Absence of suitable Rhizobia, deficiency or toxicity of a nutrient, unfavourable soil conditions, excess water logging, unsuitable pH, predators, pests are other factors, which indirectly influence the potentiality of Rhizobium strains.

The Rhizobium strains having significant potential of nitrogen fixation ranging from 50-300 kg/N/ha per season depending on the crops. Further legumes often require specific strains of Rhizobium for maximum nitrogen fixation and nodule formation. On the basis of specificities, the genus Rhizobium consists of different groups named as Rhizobium leguminoserum, which further have three biovarieties (trifolii, phaseli and viceae), Rhizobium meliloti, Rhizobium loti, Rhizobium fredii, Rhizobium ciceri, Rhizobium jampnicum, and Rhizobium spp.

Azotobacter is a heterotroph bacterium of aerobic character having the capability of fixation of dinitrogen (N2) as nonsymbiont. Azotobacter not only provides the nitrogen but also produce a variety of growth promoting substances. Some of them are indole acetic acid (IAA), gibberellins (GA), Vitamin-B, and antifungal substances. Another important characteristic of Azotobacter associated with crop improvement is excretion of ammonia in the rhizosphere (root zone) in presence of root exudates.

The benefits of Azotobacter inoculation on crop production are well known. Barley, maize, paddy, jowar, oat, sugarcane, tobacco, cotton, potato, brinjal, onion, cauliflower, cabbage, other vegetables, sunflower mustard, seasemum, linseed, tea, coffee and all type of forest fruit and flower plants are known to fix 20-30 kg. N/ha. Azotobacter also causes mineralization of fixed phosphate of soil and thus increase uptake of phosphate in plants.

Azospirillum – an associative micro-aerophilic nitrogen fixer, is commonly found in association with the roots of cereals and forage grasses. High nitrogen fixation capacity, low energy requirement and abundant establishment in the roots of cereals and tolerance to high soil temperature (30-40º C) have made it suitable under tropical conditions. Azospirillum is also found on root surface, root hairs, epidermal cells and vesicular tissues.

Azospirillum inoculants consistently help in increasing grain yield of paddy, barley, bajra, ragi, sugarcane and sorghum. It is also beneficial for vegetables, fodder crops, fruits and flower plants. Azospirillum inoculation is found to fix 20-30 kg.N/ha per crop season and maintain soil fertility in semi-tropic and tropic regions.

Indian soils are characterized as poor to medium status with respect to available phosphorus, as the native soil phosphorus is mostly unavailable to crops because of low solubility. The condition becomes harder due to the low efficiency for utilization of phosphatic fertilizers for chemical fixation in soil. Further, there is building of insoluble phosphates in soil where phosphatic fertilizers have been applied over long periods. The introduction of efficient phosphate solubilisers in the rhizosphere of crops and soils increases the availability of phosphorus from insoluble sources of phosphates and utilization of efficiency of phosphatic fertilizers such as superphosphates. Important phosphate solubilising organisms are Pseudomonas straiata Bacillus polymyxa, Aspergillus awamori, Penicillium digitatum.

Use of Azolla in rice fields has been found to increase the yield by even more than 200% in a few cases. Azolla layer may be used as biofertiliser in paddy fields or it can be cropped as a dual crop with the paddy.

Besides enriching the soil with nitrogenous compounds, Azolla can also shade out the weeds, but being a aquatic fern, the species can only be grown in wetlands or water logged fields. A few most commonly used species of Azolla are Azolla filiculoides (the species most commonly found in Hawaii), Azolla caroliniana, Azolla mexicana, Azolla microphylla, Azolla nilotica, and Azolla pinnata.

Blue-green algae are considered the simplest microscopic, living autotrophic plants, i.e. organisms capable of building up food materials from inorganic matter. Blue-green algae are widely distributed in the aquatic environment. They adapt to extreme weather conditions and are found in snow and in hot springs with water temperature as high as 85°C.

Certain blue-green algae live intimately with other organisms in a symbiotic relationship. Some are associated with the fungi in form of lichens. The ability of blue-green algae to photosynthesize food and fix atmospheric nitrogen accounts for their symbiotic associations and also for their presence in paddy fields. Blue-green algae are of immense economic value as they add organic matter to the soil and increase soil fertility. Barren alkaline lands in India have been reclaimed and made productive by inducing the proper growth of certain blue-green algae.

Type of Biofertiliser	Demand (Tonnes)
Rhizobium Azotobacter Azospirillum Blue green Algae Phosphate solublising microorgaanism	34,999 145,953 74,342 251,738 255,340
Total	762,372