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The Ureolytic Microflora in a Black Spruce (Picea mariana Mill.) Humus¹

ABSTRACT

The total and the ureolytic microflora in black spruce humus from an untreated plot and from a plot fertilized with 450 kg urea-N per ha (400 lb N per acre) 2 years before sampling was studied using incubation tests. Following the addition of 3,500 ppm of urea-N in the laboratory the total numbers of bacteria and fungi increased on the average by 332 and 9.6%, respectively, and the numbers of ureolytic bacteria and fungi increased by 359 and 18.5%, respectively. The percentages of ureolytic bacteria and fungi both increased by only 5, indicating that the increase in population was not made up of specifically ureolytic organisms. No significant population changes occurred after 3 days of incubation, when urea hydrolysis was complete.

The application of urea in the laboratory to humus from a plot treated with urea two years before sampling brought about population changes which roughly paralleled those found in humus from the untreated plot.

In any particular humus layer, the population increase occurring in the field during the two years after urea application was observed to be in general greater than that occurring during the 42 days after the application of urea to the same humus layer in the laboratory.

¹ Joint contribution from Macdonald College and Pulp and Paper Research Institute of Canada. Part of a thesis submitted by the senior author in partial fulfilment of the requirements of the Ph.D. degree at McGill University. Issued as Macdonald College Journal Series no. 552.

² Research Officer, Dept. Forestry of Canada, Quebec, and Associate Professor of Microbiology, Macdonald College of McGill University, Quebec, Canada, and Scientific Consultant, Pulp and Pap. Res. Inst. of Can., respectively.

Received for publication July 5, 1966. Accepted for publication September 28, 1966.