A calorimetric analysis of soil treated with effective microorganisms

•Effective microorganisms (EM) are a consortium of beneficial microorganisms that increases the microbial diversity of soil.•Calorimetry demonstrates the enhanced microbial activity of soil after successive applications of EM.•EM composted with a brewery fermentation tank residue suppressed part of the soil microbiota.•Soil microbial biomass carbon was determined by calorespirometry through the entire growth process.

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 Tucumán, 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 16–22 J 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.