Biomedical subjects
Publications and source records attributed to A C Gaur.
Fly ash and its different combinations with soil (w/w) were tested to explore its possible use as a potential carrier for diazotrophs and phosphobacteria. Azotobacter chroococcum, Azospirillum brasilense and Bacillus circulans showed their maximum viability in fly ash alone whereas Pseudomonas striata proliferated most in soil:fly ash (1:1) combination.
Fly ash was co-composted with wheat straw and 2% rock phosphate (w/w) for 90 days and different chemical and microbiological parameters monitored to evaluate its effect on the composting process. Fly ash addition at 20% level resulted in the lowest C/N of 16.4:1 and highest available and total phosphorus. Increasing the addition of fly ash from 40 to 60% (w/w) did not exert any detrimental effect on either C:N or the microbial population.
Fly ash was characterized for the leaching potential of some major and minor constituents and then added to soil at 20, 40, 60 and 80 t/ha with N and P fertilizer to evaluate its effect on nutrient uptake and soybean yield singly as well as in combination with an efficient phosphate solubilizer Pseudomonas striata. The application of fly ash at 40 t/ha in conjunction with P. striata inoculation improved the bean yield and P uptake by grain. The available phosphorus of soil also showed an upward trend. The fly ash did not exert any detrimental effect on the population of inoculated bacteria. However, the uptake of trace elements did not improve significantly.
Humate-decomposing microorganisms were isolated from alluvial soil, farmyard manure and peat by direct plating and enrichment techniques. Peat was found to harbour more of these organisms than soil and manure. Out of 21 actinomycetes and 6 fungi 9 and 3 isolates, respectively, were found to utilize manure-humate as a sole source of carbon and to a less extent as a source of both carbon and nitrogen in liquid medium. These efficient cultures were identified as Streptomyces spec. (A 11 and A 12). Str. candidus, Str. violaceoruber (A 41 and A 42), Str. rubescens, Str. garyphalus, Str. viridochromogenes, Fusarium solani, Aspergillus fumigatus, and Penicillium roseopurpureum. Additional sources of carbon and nitrogen stimulated microbial degradation of humate. Only five isolates formed a zone of decolourization on humate-containing solid medium. Soil humic acid was utilized by Str. candidus as a sole source of carbon and nitrogen, however, F. solani utilized it only in the presence of additional carbon and nitrogen sources. Extent of soil-humate degradation was less than manure-humate.
Bacteria Pseudomonas striata, Bacillus polymyxa, B. megaterium and B. pulvifaciens, and fungi Aspergillus awamori, A. niger and Penicillium digitatum dissolve tricalcium phosphate and, much less, Mussorie and Udaipur rock phosphate. The solubilizing power of fungi was higher than that of bacteria, the highest being with A. awamori and A. niger, and with P. striata. Electron microscopy of the various cultures showed an electron-dense layer on the bacterial surface after negative staining. The size of phosphate particles decreased by the microbial action, with tricalcium phosphate from 140--250 to 30--90 nm after three weeks of incubation.
Simazine, even at normal rates of application, showed toxicity to bacteria fungi. It was less toxic to actinomycetes, since toxicity up to 20 ppm of the herbicide was not observed. On the contrary, the normal rate of simazine stimulated both Azotobacter and actinomycetes population. The interaction of simazine with soil ecological factors, such as temperature, moisture, pH, and organic matter, affected soil microbial population differently. Simazine was relatively less toxic to bacteria under acidic and alkaline conditions of soil; they were not affected at 15 degrees C. Actinomycetes were comparatively not adversely affected even with 200 ppm of simazine under high soil moisture regime. The stimulatory effect of simazine on Azotobacter was also confirmed under different ecological conditions. The incorporation of 2 per cent of organic matter in soil mitigated the toxicity of simazine in respect to soil fungi. Simazine also appeared to be less toxic to soil fungi at lower temperatures, under acidic and alkaline conditions of soil, as well as under high moisture regime.
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