Occurrence and distribution of azotobacter species in some soils of Assam and the response of rice and wheat crops to their inoculation

Abstract

It has been now recognised that productivity of agriculture cannot be maintained solely by input of energy and fertilizer. Biological components that maintain productivity cannot be ignored any longer. Natural productivity of soil depends upon many known and unknown interaction of these components. Biological nitrogen-fixation is one of the most important contributing factor the nature has provided for continuous input of nitrogen to maintain plant productivity. Chemical fertilizer, although increases crop productivity considerably, the unjudicious use of it in large quantity has created associated problems which in the long run may destroy the entire biological productivity system and consequently the soil may turn into a dead mass of substance. The symbiotic nitrogen - fixation although is very important from agricultural point of view, it has many limitations. On the other hand, the non-symbiotic nitrogen - fixation is advantageous on many counts. The non-legume biofertilizer are now recognised as most important source of nutrient suppliers in agriculture as well as in natural habitats. Not only these organisms are abundant in nature but these can also be used suitably as biofertilizer when agricultural soil is required to be enriched with specific types of it. Several types of free-living nitrogen-fixing microorganisms are now in use in India and other countries as biofertilizers. Biofertilizers of different brand names are now available in our country also. The role of Azotobacter as free-living nitrogen-fixing bacteria has been recognised in the early part of the present century. Soviet Union has started using them as biofertilizer as early as in 1930 A.D. It was found that the role of Azotobacter is not restricted to nitrogen - fixation alone. They also stimulate plant growth, break dormancy of seeds and resist soil-borne diseases. They can establish well in the rhizosphere zone and therefore are most effective in improving plant growth particularly of cereals. In India, bacterization with Azotobacter was...