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The microbiology of four steamed soils
Published online by Cambridge University Press: 27 March 2009
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Four soils, sterilized by steam at 100° C, with unsteamed controls for three soils, were examined at intervals up to 62 days to study the microbiology in relation to the abundance of ammonia, nitrites and nitrates of all the soils, the C/N ratios of two, and the pH and moisture content of three. After steaming, the soils were flooded with sterilized tap water equivalent in amount to 3 in. of rainfall at intervals varying with the particular soil. The soil of the first trial remained under water until very near the end of the experiment. In all the soils, the production of ammonia up to 14 days after steaming was associated with increased biological activity, generally a multiplication of bacteria associated with multiplication of Protozoa. The production of nitrites and nitrates was associated with a similar biological activity. Those bacteria that survived steaming had simple growth requirements as compared with those of the subsequent microflora. The Protozoa showed a series of ‘pulses’ of maximum and minimum abundance and there was also a succession of species in all the soils. A predilection of Protozoa for certain bacteria was shown by the association of certain species with particular groups of bacteria identified by Gram's staining. In two of the soils, there were ‘pulses’ of maximum and minimum abundance of diatoms, and in one soil diatoms possibly affected soil texture. The investigation showed that despite the contrasting characters of the soils, the major chemical changes were almost wholly attributable to biological activity, and that after steaming the same general reactions occurred in all. The investigation proved the importance of considering the microbiology of steamed soils as a problem in ecology.
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- Copyright © Cambridge University Press 1952
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