BIOFERTILIZERS

BIOFERTILIZER:

The term Bio fertilizers refers to the use of living organism to increase the fertility of soil. It is well known that many microbes specially bacteria are able to fix atmospheric nitrogen.For example Rhizobium which lives in the roots of leguminous plants, helps in the fixation of atmospheric nitrogen into the compounds of nitrogen like nitrate and nitrite. PGPR ( Plant growth promoting rhizobia) and PSM (Phosphate solubilizing microbes)can be considered as fertilizers. Bio fertilizers are also considered as microbial fertilizers .For the preparation of biofertilizer , Rhizobium inoculant is most important to be used.

Specific inoculants:

It can be classified into three categories:

• Nitrogen fixers which are free living ,associative or symbiotic in nature

• Phosphate solubilizers or phosphate mobilizers

• Plant growth promoters or plant health promoter or plant disease suppressor.

In addition to Rhizobium other bio fertilizers are blue green algae as

1Azotobacter inoculant

2 Azospirillum inoculant

3 Phosphate solubilizing microbes

4 Azola as inoculum

5 Plant growth promoting, Rhizobium

1 BLUE GREEN ALGAE AS INOCULANT:

The Cynobacteria are either single celled or consist of branched or unbranched filament . Some of them possess a peculiar structure known as heterocyst and all heterocyst formed ,can fix nitrogen from air. Recently some cyanobacteria without heterocyst have also been found to fix nitrogen.Members of which are used as bio fertilizers for field application are species of Tolypothrix, Nostoc , Anabaena. As early as 1939 P.K De suggested that fertility of the tropical rice field was largely due to the activity of nitrogen fixing blue green algae. Besides nitrogen,these algae are also known to provide the top plants with many other useful organic substances like growth factors and vitamins.

• Production of algae for field application

Based on the natural ecology of these algae, a simple rural oriented open air method of production has been developed at the IARI ,New Delhi . The basic principle is to grow them in natural sunlight under conditions stimulating these in the rice field The starter culture is a soil based mixture of Tolypothrix, Nostoc, Anabaena and Plectonema is supplied by the Indian Agriculture Research Institute

Methods of field application

Algae are applied at the weight of 10 kilogram per hectare over the standing water in the field .One week after transplantation, the field is kept waterlogged at least for a couple of days, immediately after algal application done.

Algae are living systems and once they established ,their biological activity continues. Normally continue inoculation for 3 to 4 cropping seasons, results in an appreciable population built up without any further inoculation.

2 AZOTOBACTER AS INOCULANT:

Azotobacter is a free living nitrogen fixing bacterium. Genus Azotobacter are rod shaped large organism , measuring the size of 2 to 7 Micron – 1 to 2.5 microns. The cell size and shape vary considerably with species, strains, age of culture and growth conditions . A unique differentiating character is the ability to form pigment . Aged culture of Azotobacter chrococcum form an insoluble black round pigment.

Preparation and use of inoculant:

1 Agar slope based culture: Azotobacter inoculant is prepared in half litre bottles by growing Azotobacter chrococcum on Agar slants. In every half litre bottle there will be about 40 to 50 million Azotobacter chrococcum cells ,the colony are also grown on agar spread ,on the inner surface of the bottle . The young cells are not pigmented while the older cells are pigmented.

2 In India, mostly carrier based (charcoal plus soil or lignite) is used. AZOTOBACTER inoculant have almost replaced liquid cultures and Agar slope cultures. Media used for Azotobacter cultivation are:

• Mannitol salt Agar medium

• Burk’s medium

• Jensen’s medium

Methods of application

• Direct method of seed inoculation

Azotobacter grown on Agar plants in 500 ml bottles is scrapped by adding water and shaked it and then sprinkled on the seeds. The seeds are then mixed so that material is evenly distributed on them and then allowed to dry in shade before sowing.

Transplanted crops

The method of seed inoculation with carrier based Azotobacter culture is similar to that of Rhizobium inoculation .However for transplanted crops, the seeds are dipped in the slurry of the carrier based inoculant ,for 10 to 30 minutes ,depending upon the crop species and then these are planted immediately.

The last and most important is inoculations are done by pouring the slurry near the root zone. The inoculant is also mixed with farmyard manure near the root zone.

Advantages of Azotobacter inoculant:

• Culture of Azotobacter form considerable quantity of biological active substances. For most among these are the source of vitamins, pantothenic acid,biotene and gibberellins.

• Azotobacter has ability to produce antifungal, antibiotics and fungistatic compounds against pathogens like Fusarium, Alternaria and Trichoderma.

• It has ability to fix high amount of nitrogen

• it has faster growth rate

• production of plant growth promoting substances

• Ability to have antagonistic effect

3 AZOSPIRILLUM AS INOCULANT:

The bacterium Azospirillum is gram negative, motile generally spiral in shape and contains Poly beta hydroxy butyrate granules. Four species of azospirullum was described up to 1984 ,which are used as bio fertilizers.

Preparation of inoculant

For mass multiplication of a spirallum. Organism is allowed to grow in flask containing media having macro and micro nutrients with Malate as carbon source and yeast extract as a source of vitamin. This medium is incubated at 35 to 37 degrees Celsius for three days then there is a good growth .This growth is taken in distilled water to produce broth and this broth is mixed with carrier and this carrier based culture is packed in polythene pouches.

Careers soil and farmyard manure in the ratio of 1:1 sterilised for three hours or for three days, has been found to be best suited as a carrier for Azospirillum bacteria . This bacteria is able to survive in this carrier up to six months

Advantages of Azospirillum inoculant:

• it has been found that this bacteria increases the yield of many crops .example- rice, wheat, barley and sorghum

• this bacteria produces plant growth hormones in pure cultures

4 PSM AS INOCULANT:

Next to nitrogen,phosphorus is most important nutrient which is required for plants. In most of the soil, phosphorus is in unavailable form and hardly about 1- 2% of it is incorporated into the above ground parts of plants. PSM Include various bacteria, fungi and actinomycetes forms which have to convert insoluble inorganic phosphorus into simple and soluble form .These include members of genus Pseudomonas, Bacillus,Penicillium, Micrococcus ,Fusarium and Aspergillus. These are some PSM and these efficient microbes have capacity to solubilize chemically soil phosphorus and rock phosphorus from different sources by developing improved techniques for isolation of microbes .New efficient bacteria such as Pseudomonas seritia, Bacillus polymixa and fungi like Aspergillus awamori has been selected for preparation of carrier based inoculant.

Advantages of PSM:

• They can solubilize tricalcium phosphate ,rock phosphate and Iron aluminium phosphate by production of organic acid

• They can produce mono di and Tri carboxylic acid in soil which help in solubilization of phosphate

• They can increase the grain yield of crops.

5 AZOLLA AS INOCULANT:

The recognition of Azolla as an organic manure in rice cultivation was first shown in north Vietnam in 1957.Azola is a tiny floating, freshwater fern and is omni present in nature . It has dorsal and ventral lobe .The dorsal lobe is green and has a blue green algal symbiont i.e Anabaena azolae ,within a central cavity. The heterocyst of the symbiont Anabaena is site nitrogen fixation.

Methods of using Azolla as biofertilizer:

Two methods of asola applications have been adopted

• Dual cropping with rice when the Fern is grown side by side with principal crop for sometime

• Azolla has to be grown initially in small earthen pots, near the cultivated field then the biomass is applied to the rice fields at the rate of about 10 tonnes per hectare by incorporating it into soil before transplantation of the rice seedling. Chinese and Vietnamese farmers usually follow the dual cropping of rice and Azolla side by side.

Azolla is the only green manure which can be cultivated as an intercrop with the rice in flooded condition and has no bad detrimental effect on rice Although its biomass is less in planted field than in unplanted fields.

Limitations of using Azolla as biofertilizer

• Storage value of fresh Azolla is low and hence difficult to transport for long distances

• Phosphate is the most important for its growth

• High temperature inhibits its growth. Thus there is an urgent need to develop dried Azolla technology and to evolve varieties of Azolla which can sexually produce spores that can with- stand high temperature and low phosphate application.