The soil is influenced by the roots of plants because the exudate radicals affect its physical, chemical, and biological processes. The aim of this research was to evaluate the microbial activity of soils cultivated with yacón (Smallanthus sonchifolius Poep. & Endl) H. Robinson and inoculated with microorganisms which promote plant growth. The experimental design used was randomized blocks with three repetitions per treatment. Each repetition corresponded to a 3m x 3m plot with 25 plants, in 5 cultivation lines with a distance of 70 cm apart. Four treatments were applied at the time of plantation. These consisted of yacón propagules inoculated with Azospirillum brasilense (T1) and native mycorrhizal fungi (T2) inoculated with the microbial consortium (T3). In the control treatments, the propagules were not inoculated with these microorganisms (T0). Soil samples were collected in lots cultivated with yacón located in the Province of Catamarca, in the northwest of Argentina. The samples were collected at the time of implantation and harvest during three agricultural cycles. The total Biological Activity (TBA) of the collected samples was determined by Fluorescein Diacetate Hydrolysis. The TBA of the soil was affected by the different crop treatments, which rose in the analyzed soils and was statistically different from the control treatments. Significant differences were also observed between the TBA of the soils at the beginning of the crops in comparison with the recorded values of the crop at the time of harvest. The inoculation of yacón propagules with A. brasilense and native mycorrhizal fungi affects the TBA of the cultivated soils marking a significant increase.