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.