Article: Burton Keakile
Bio-fertilizers are natural fertilizes which are living microbial inoculants of bacteria, algae, fungi alone or in combination and they augment the availability of nutrients to the plants. The role of bio-fertilizers in agriculture assumes special significance, particularly in the present context of increased cost of chemical fertilizer and their hazardous effects on soil health.
Several microorganisms and their association with crop plants are being exploited in the production of bio-fertilizers. They can be grouped in different ways based on their nature and function. Rhizobium is a soil habitat bacterium, which colonizes legume roots and fixes atmospheric nitrogen symbiotically. The morphology and physiology of Rhizobium vary from free-living condition to the bacteria of nodules. They are the most efficient bio-fertilizer as per the quantity of nitrogen fixed concerned.
Azolla is a free-floating water fern that floats in water and fixes atmospheric nitrogen in association with nitrogen fixing blue green alga Anabaena azollae. Azolla either as an alternate nitrogen sources or as a supplement to commercial nitrogen fertilizers. Azolla is used as bio-fertilizer for wetland rice and it is known to contribute 40-60 kg N/ha per rice crop.
The group of bacteria that colonize roots or rhizo-sphere soil and beneficial to crops are referred to as plant growth promoting rhizobacteria (PGPR). The PGPR inoculants promote growth through suppression of plant disease termed Bio protectants, improved nutrient acquisition termed Bio fertilizers, or phytohormone production termed Bio stimulants. Species of Pseudomonas and Bacillus can produce as yet not well characterized phytohormones or growth regulators that cause crops to have greater amounts of fine roots which have the effect of increasing the absorptive surface of plant roots for uptake of water and nutrients. These PGPR are referred to as Bio stimulants and the phytohormones they produce include indole-acetic acid, cytokinins, gibberellins and inhibitors of ethylene production.
Phosphate solubilizing microorganisms is another form of a bio fertilizer. Several soil bacteria and fungi, notably species of Bacillus or Penicillium secrete organic acids and lower the pH in their vicinity to bring about dissolution of bound phosphates in soil.
Bio fertilizers have several advantages. They are eco- friendly as well as cost effective. Bio fertilizer contains microorganisms which promote the adequate supply of nutrients to the host plants and ensure their proper development of growth and regulation in their physiology. They also harness atmospheric nitrogen and make it directly available to the plants. Bio fertilizers can also protect plants from soil borne diseases to a certain degree and also help in increasing the crop yield.
