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Influence of Simulated Fall and Spring Conditions on the Soil System: II. Effect on Soil Nitrogen¹

ABSTRACT

Stored and fresh Wood Mountain loam samples were wetted to 20% moisture using either water, Ca(NO₃)₂, or (NH₄)₂SO₄ solutions. Half of the samples were sterilized with ethylene oxide. Fall conditions were imposed by incubating samples at diurual temperatures of 14 to 3C and early spring conditions by slow freezing to –23C followed by incubation at 14 to 3C or 8.5C. Exchangeable NH₄-N, NO₃-N, and microbial counts were determined at appropriate intervals.

In the unamended and NO₃-amended soils, freezing followed by 16 days incubation at 14 to 3C had a bactericidal effect and resulted in a much lower rate of nitrification than freezing followed by incubation at 8.5C. Where NH₄ had been added the bactericidal effect was not as great and there was no difference in nitrification between the two incubation temperatures.

Incubation at low temperatures impeded nitrification more than ammonification which resulted in an initial buildup of exchangeable NH₄.

Ethylene oxide was an effective soil sterilant but caused a small increase in the exchangeable NH₄.

Freezing followed by incubation at low temperatures increased the exchangeable NH₄ in sterile soils but did not affect the NO₃ content. There was evidence of an interaction between the length of soil storage and the various treatments (viz, freezing, sterilization, etc.).

¹ Contribution from the Research Station, Research Branch, Canada Dept. of Agriculture, Swift Current, Saskatchewan.

² Soil Chemist, Soil Microbiologist, and Soil Chemist, respectively.

Received for publication August 31, 1970. Accepted for publication February 1, 1971.