The use of synthetic fertilizer in agriculture results in the deterioration of soil conditions and environment. The continuous application of artificial fertilizer leads to death of soil literally. The harmful effect of synthetic fertilizer has led to the alternative fertilizer research. Biofertilizers are one such alternative fertilizer which is nothing but the preparation containing micro organisms that helps agricultural crops to uptake nutrients more efficiently. In nature beneficiary micro organisms may not present in optimal level in the fields to observe the required benefit. Therefore artificial cultures of selected micro organisms holds promising role in developing the microbial fauna in the field. The biofertilizers are used as one of the critical components of the nutrient management and are easily renewable and cost effective as compared to the artificial fertilizers.
Biofertilizers can be effectively used in cultivation of rice and other staple crops; commercial crops such as cotton, sugarcane, etc., and in vegetables and fruit cultivations. Biofertilizers provides phosphorous and nitrogen nutrients to plants via N2 fixation and phosphorous solubilization mechanisms. Biofertilizers are one of the important components of organic farming that enhances the plant growth and yield; also improves health and fertility of soil. The application cost of Biofertilizers when compared to the synthetic fertilizer is very less, hence will lower the cost of agricultural activity and results in improved economic conditions of the farmer. The problems faced with chemical fertilizers such as increased salinity and chemical residues can be solved with application of biofertilizers, which ensures a healthy environment for upcoming future generations. The crops grown with biofertilizers are considered healthier as the plants are allowed to grow and produce fruits in a natural ways. Biofertilizers also gives protection to crops against diseases and insect pest, hence reduces the application of pesticides in the field.
Various strains of micro organisms are studied for their role in crop yield improvement. Soil bacteria Rhizobium sps colonizes in the roots of legume plants and fixes nitrogen from atmosphere to soil. The association of Rhizobium sps is symbiotic, where the host plant gives shelter to the bacteria and in return the bacteria supplies vital nitrites to the host plant. Azotobacter sps is other beneficiary inhabitant of soils fixes nitrogen. These bacteria synthesize slime that helps in aggregation of soil. Azospirillum sps are found in root cortex of graminae and leads symbiotic relationship with host plant. These gram negative bacteria fix nitrogen and proliferates both in aerobic and anaerobic conditions. Azospirillum inoculation, give host plant drought tolerance and disease resistance benefits apart from N2 fixation.
Cyanobacteria sps (blue green algae) both symbiotic as well as free-living are beneficiary for rice crops. Water fern (Azolla sps) also fixes nitrogen with help of symbiotic algae Anabaena. Azolla sps has been used in rice cultivation as biofertilizer due to high nitrogen contribution. The secreted acid by Pseudomonas sps and other phosphate solubilizing microorganisms lower pH content of soils and helps in dissolution of phosphates that are bound in soils. Glomus sps and other intra-cellular fungi mediate transfers nutrients like phosphorus, zinc and sulphur from soil to root cortex of host plants. The other class of bacteria's which colonizes roots and beneficial for crops are known as plant growth promoting rhizobacteria (PGPR). PGPR promote crops growth through either of the following mechanisms. PGPR might help in suppressing plant diseases called Bioprotectants or they might help in nutrient acquisition called Biofertilizers or might help in phytohormone production called Biostimulants. Few PGPR might helps in developing fine roots and thereby increasing the absorptive area of plant roots, which help in uptake of more water and nutrients. PGPR produces plants hormones such as indole acetic acid (IAA), gibberellins and cytokinins.
Despite of tremendous positive results, biofertilizers has yet to get large scale applications in agriculture due to varied response of crop species to inoculation medium containing bacterial strains. Bacteria with good competitive and high saprophytic mode become the critical factors determining the success of biofertilizers. More research is required in the field of biofertilizers to develop strains that can be easily inoculated into host systems and proves effective in field conditions. The current traditional chemical fertilizer applications has resulted in environmental pollution and increased cost of agricultural activity makes tremendous potential for Biofertilizers research in future.
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