Production and Application of Phosphate Solubilizing Bacteria as Biofertilizer: Field Trial at Maize Field, Uchalan, Burdwan District, West Bengal.

Development of a nation is directly proportional to the amount of food or nutrient available to the population. Growth of the human population creates demand for more food grains. To supply food grains according to the demand, fertilizers are used. A fertilizer is any substance that is used for increasing the productivity of the soil. It promotes soil fertility by adding nutrients in the soil, which helps in plant growth. Fertilizers which are composed of raw chemicals in solid or liquid form manufactured in factories targeting the nutritional requirement of the plants are by definition called a “chemical fertilizer”. Nitrogen, Phosphorous, Potassium together called NPK are normally present in these chemical fertilizers along with other nutrients (Youssef et al.,2014). The substances are normally present in a form that is easily absorbed by the plant. But the use of chemical fertilizers has some harmful side effect on the environment (Usman et al.,2015). Important issues include groundwater contamination especially nitrogen compounds, they break down into nitrate and accumulates in the groundwater. Biofertilizers can be used as supplements of chemical fertilizers; they are relatively inexpensive and renewable sources of plant nutrient. Biofertlizers are selected strains of microorganisms which are beneficial to the growth of the plants. These microorganisms are cultured in laboratory, mixed with suitable carrier materials and then applied to the fields. They maintain soil health, minimizes pollution of the environment by lowering the use of chemicals (Tripti et al., 2012). Biofertilizers are used to treating seeds, plantlets, grown plants. The popularity of the biofertilizers are due to its eco-friendly, non hazardous and non- toxic nature. The living microorganisms colonizes the rhizosphere or colonizes the interior of the plant, they promotes growth by increasing the availability of the nutrients and helps in the breakdown of inorganic substances into organic form, increasing the supply of growth stimulus to the seeds of crops, plant surfaces and even in the soil can help in greater productivity. Examples of bio fertilizers are numerous and varied like, Rhizobium, Azospirillium and Azotobacter – Nitrogen fixing biofertilizers. Pseudomonas, Bacillus, Aspergillus, are examples of PSB or Phosphate solubilising biofertilizer. Mycorrhiza is an example of Phosphate mobilizing biofertlizer. Pseudomonas species are also commercialized as Plant growth promoting biofertilizers. Soil microorganisms play an important role in maintaining the ecological balance, they participate actively in carbon, nitrogen, phosphorus, potassium, sulphur recycling in nature and thus facilitate uptake in the plants (Ansari et al., 2015).

The role of microorganisms in converting insoluble form of nutrient into soluble form is well known. After nitrogen, phosphorus is second in terms of importance for growth in plants. Phosphorous is 0.2% of the dry weight in plants. Phosphorus is obtained by the plant as phosphate anions. Phosphate solubilizing bacteria possess capability to convert phosphorus from insoluble to soluble form (Keneni et al., 2010). Phosphatic fertilizer when applied to the soil it has been seen that only a small amount is actually utilized by the plants. In India, it has been estimated that about 98% of the soil have some amount of deficit in phosphorus. Chemical fertilizer having phosphorus have a disadvantage, inorganic phosphates when applied to the soil are immobilized and thus not totally available to the plant (Karpagam and Nagalakshmi, 2014). PSBs or Phosphate solubilizing bacteria helps in converting phosphorus into soluble forms by acidification by organic acids, chelating oxo acids from sugars. They also produce enzymes like phosphatase enzymes that help in further degradation. Inoculation of PSBs in soil or near the rhizosphere of the plants has shown to promote growth of plants as a stimulatory effect. Plant roots can take up different forms of phosphorus like H PO , HPO 2-, this take up normally depends upon the soil 2 4 4 pH, temperature, moisture content and other nutrients or minerals present in the soil (Rajsekaran et al,2012).