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The Number of Colonies on Plaques of Soil Made from Samples Taken from Various Horizons

Cornell University

ABSTRACT

Samples of soil were collected from definite types of soil. They were obtained from thirty-six different locations. From each location, the samples came either from definite horizons of the soil, or from definite distances from the exposed surface downward. Magnesium ammonium phosphate was the only inorganic material added to the soil in making plaques for determining the presence of organisms capable of producing macroscopic colonies. Employing this method, the numbers of colonies appearing on the surface of the plaques were counted. This gave a comparison of the population of a certain group of organisms inhabiting the soils. The identity of these was not determined. It is concluded that organisms capable of producing macroscopic colonies permeate the various horizons of the soil and are found in the unweathered material which may be fifteen feet below the exposed surface of the soil.