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

Abstract

AbstractExperiments 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.