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Measurement of Microbial Thermogenesis in Soil¹

ABSTRACT

Microbially induced temperature changes were measured in laboratory soil lots without vacuum insulation or adiabatic control. The instrumentation consisted of thermistors, a 52-point stepping switch, and a bridge-type strip-chart recorder. The thermistors were variously positioned in soil quantities of 25 g., 3.3 kg., and 39.6 kg. The temperature changes were measured on an alluvial sandy loam, unamended or amended with either alfalfa meal or sucrose, at rates ranging from 0.1 to 1.0%. Temperature elevations of the order of 1.5°C. were observed in the 39.6 kg. uninsulated soil lots containing 1.0% alfalfa meal and 5.3°C. in 3.3-kg. soil lots similarly amended and incubated in insulated containers. Addition of 1.0% alfalfa meal to 25 g. soil in uninsulated glass containers led to a maximum rise of 0.22°C.

In other work, soil temperature values were determined in various soil lots given lesser rates of organic amendments. The data obtained show that organic residues in soil can cause local areas within which microbially induced thermogenesis is measurable for intervals of several days, or even weeks, despite the relatively high specific heat capacity and conductivity of moist soil.

¹ Contribution from the Soil and Water Conservation Research Division, ARS, USDA, Colorado Agr. Exp. Sta., Ft. Collins, cooperating. Presented before Div. III, Soil Science Society of America, Dec. 7, 1960, at Chicago, Ill.

² Microbiologist and Soil Scientists, ARS, USDA, Ft. Collins, Colo., Tempe, Ariz., and Ft. Collins, Colo., respectively.

Received for publication May 16, 1961. Accepted for publication July 11, 1961.