Yeasts in soils spray-irrigated with dairy factory wastes

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Abstract
An examination was made of the yeast flora of eight soils under pasture which were spray-irrigated with dairy factory wastes, also of the yeast flora of some of the irrigants and of leaves of pasture plants from an irrigated site. Provided that the irrigant contained lactose, numbers of yeasts in irrigated soils increased by 50 to 1,000 times; where lactose had been extracted from the irrigant there was no increase in numbers. After irrigation with wastes containing lactose, the composition of the yeast flora changed from one dominated by Candida curvata or Cryptococcus terreus to one in which Candida humicola or Trichosporon cutaneum was most often the dominant species. There was no qualitative change in the yeast flora of a soil irrigated with wastes from which lactose had been extracted. Yeasts present in the irrigant, principally Saccharomyces fragilis, Candida pseudotropicalis, Candida mycoderma, and Candida krusei, were recovered only from very recently or very heavily irrigated soils; the species which increased in numbers were those already in the soils. Similarly, yeast species from the irrigant could be recovered from the leaves of pasture plants only within 24 hours of spraying. After lactose, or lactose plus phosphate or urea, had been applied to turfs of Taita soil in pots, numbers of soil yeasts increased. C. curvata was the dominant yeast species in untreated soil. With all treatments C. humicola was at first the dominant soil yeast, but it remained dominant only in soil treated with lactose plus phosphate. C. curvata returned to dominance in soil treated with lactose plus urea. In soil treated with lactose only, a succession of species became dominant, first C. humicola, then C. curvata again, and, at the end of the experiment, when C. krusei had assumed proportions equal to those of C. curvata, numbers of Lipomyces spp. were greater than those of any other yeast group.

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