Effective microorganisms or EM is a consortium of beneficial microorganisms (primarily photosynthetic and lactic acid bacteria, yeast, actinomycetes, and fermenting fungi) that can be applied as inoculants to increase the microbial diversity of soil. Two fields of sugar cane in the province of Tucuman, Argentina were treated with either EM containing brewery fermentation tank residual yeast (YS) or just EM (NYS). The outcome was 1000 kg Ha(-1) less of sugar cane harvested from YS field. The aim of this work was to analyze both soils to find out if calorimetry could assess the negative effect of yeast. Mass specific thermal power-time curves were obtained during 100 or more h of measurement. Once a day, a vial containing NaOH solution was introduced into the calorimetric ampoule to determine CO2 evolution. A plot of log SMB (soil microbial biomass) as a function of log p gave a similar relation as previously reported for those samples that showed an energy expenditure of 16-22J cm(-3) CO2 respired. Thus, soil microbial biomass could be determined during microbial growth. Results showed that yeast suppressed the activity of part of the soil microorganisms. Also, soil microbial activity increased with time in NYS due to successive applications of EM. (C) 2013 Elsevier B.V. All rights reserved,