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Influence of Simulated Fall and Spring Conditions on the Soil System: III. Effect of Method of Simulating Spring Temperatures on Ammonification, Nitrification, and Microbial Populations¹

ABSTRACT

Experiments were carried out to determine (i) how different methods of simulating spring temperatures affect soil microbial activity, and (ii) the interactions between different types and amounts of added-N and these temperature effects.

In soil amended with mineral-N, ammonification (change in NO₃-N + NH₄-N) was inversely proportional to the amount of added-N when incubated at 8.5C, but ammonification was not affected by amount of N when incubated at fluctuating temperatures. When peptone-N was added to soil, ammonification was unaffected by the method of simulating spring temperature conditions.

In unamended soil and soil amended with 10 ppm NH₄-N, nitrification was greater at 8.5C than at square-wave 14 to 3C. When peptone-, NH₄-, or NO₃-N was added to soil, nitrification at 8.5C was generally equivalent to that at square-wave 14 to 3C, but less than that at sine-wave 14 to 3C. Where peptone-N was added nitrification was > NH₄-N added > NO₃-N added.

In unamended soil, fluctuating temperature cycles were deleterious to the three major groups of microorganisms but were particularly detrimental to the nonsporeforming, gramnegative bacteria. Square-wave fluctuating temperature was more deleterious than sine-wave; the constant temperature regime was not deleterious. The deleterious effect of fluctuating temperatures was partially alleviated by addition of 25 ppm NH₄-N.

It was suggested that the protoplasmic materials released from the cells killed as a result of the fluctuating temperatures served as a ready source of N and energy substrate (much like the peptone amendment) for use by the surviving microbial populations.

¹ Contribution from the Research Station, Research Branch, Canada Agr., Swift Current, Sask. Presented in part before Div. S-3, Soil Science Society of America, Miami, Fla., Oct. 31, 1972.

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

Received for publication October 27, 1972. Accepted for publication January 18, 1973.