an appropriate manner, EM can significantly increase the effects of these practices [4]. Originally, EM was developed as an alter-native to pesticides and chemical fertilizers. However, in the lasttwo decades the utilization of EM has expanded to the treatmentof water and wastewaters, odor control, farm and animal health,human health many industrial treatments [5]. This consortium ofmicroorganisms produces accelerated breakdown of proteins, sug-ars, fats and fibers, and thus, promotes rapid organic matter decom-position. EM works in two primary ways: (i) competitive exclusionof harmful microorganisms and (ii) by production of beneficialproducts such as enzymes, organic acids, amino acids, hormonesand antioxidants that promote the health of the environment [6].EM technology is used in a farm located in the southwest ofTucumán province, Argentina. However, during 2011 besides EM,the farmer tried EM composted with the residual yeast (Saccha-romyces spp.) obtained from brewery fermenting tanks in a sugarcane field. The outcome was 1000 kg Ha−1less of sugar cane than inthe field treated with just EM. The aim of this work was to find out,by means of isothermal calorimetry: (i) how the yeast affected soilmicrobial activity and (ii) the effect of EM on soil microbial activity