Biotechnology and Bioinformatics (1+1)

6.3.1.Introduction

The term 'Biofertilizer' itself means 'Live Fertilizer'. 'Biofertilizer' is a substance which contains living microorganisms which, when applied to seed, plant surfaces, or soil, colonizes the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant.

Contain live or latent beneficial microbes which help to

• fix atmospheric nitrogen,
• solubilize and mobilize phosphorus,
• translocate minor elements (Zinc, Copper, etc.,) to the plants,
• produce plant growth promoting hormone s, vitamins, amino acids and
• control plant pathogenic fungi.

Biofertilizers are extremely advantageous in

• Enriching the soil fertility and fulfilling the plant nutrient requirements by supplying the organic nutrients through microorganism and their byproduct.
• Biofertilizers do not contain any chemicals which are harmful to the living soil.
• Biofertilizers are eco-friendly organic agro-input and more cost effective than chemical fertilizers.
• Biofertilizers like Rhizobium, Azotobacter, Azospirillum and blue green algae (BGA) are in use since long time ago.
• Rhizobium inoculant is used for leguminous crops.
• Azotobacter can be used with crops like wheat, maize, mustard, cotton, potato and other vegetable crops.
• Azospirillum inoculants are recommended mainly for sorghum, millets, maize, sugarcane and wheat.
• Blue green algae belonging to gene ra Nostoc, Anabaena, Tolypothrix and Aulosira fix atmospheric nitrogen and are used as inoculants for paddy crop grown both under upland and low land conditions.
• Anabaena in association with water fern Azolla contributes nitrogen up to 60 Kg/ha/season and also enriches soils with organic matter.
• Other types of bacteria, so-called Phosphate solubilising bacteria like Pantoea agglomerans strain P5, and Pseudomonas putida strain P13 are able to solubilize the insoluble phosphate from organic and inorganic phosphate source.
• In fact, due to immobilization of phosphate by mineral ions such as Fe, Al and Ca or organic acids, the rate of available phosphate (Pi) in soil is well below plant needs.
• In addition, chemical Pi fertilizer is also immobilized in the soil immediately so that less than 20 percent of added fertilizer is absorbed by plants. Therefore, reduction in Pi resources, on one hand, and environmental pollutions resulted from both production and applications of chemical Pi fertilizer, on the other hand, have already demanded the use of new generation of phosphate fertilizers globally known as phosphate solubilizing bacteria or phosphate biofertilizers.

The significance of biological nitrogen fixation in aquatic ecosystems has brought out the utility of biofertilization through application of heterocystous blue–green algae and related members. This assumes great importance in view of the increasing costs of chemical fertilizers and associated energy inputs that are becoming scarce as also long– term environmental management.

Azollae, a free-floating aquatic fern fixing atmospheric nitrogen through the cyanobacterium. Anabaena azolla, present in its dorsal leaves, is one of the potential nitrogenous biofertilizers. Its high nitrogen-fixing capacity, rapid multiplication as also decomposition rates resulting in quick nutrient release have made it an ideal nutrient input in farming systems.

Azolla is a heterosporous fern belonging to the family Azollaceae (Salviniaceae) with seven living and twenty extinct species. Proliferation of Azolla is basically through vegetative propagation but sexual reproduction occurs during temporary adverse environmental conditions with the production of both microsporocarp and megasporocarp.

Biofertilizers add nutrients through the natural processes of fixing atmospheric nitrogen, solubilizing phophorus, and stimulating plant growth through the synthesis of growth promoting substances. Biofertilizers can be expected to reduce the use of chemical fertilizers and pesticides.