This work deals with the heat transfer phenomena in agricultural soils exposed to microwave (MW) fields to disinfect them eliminating dangerous organisms without using pesticides. The soil, approximated to a transmission line model, is supposed to be subject to an incident plane wave coming from a horn antenna working at 2.45GHz. Assessing the dielectric constant as a function of the soil water content, with the present model, it was possible to evaluate the power absorption for the irradiated ground and, especially, the increase in temperature and its profile as a function of the exposure time. In this way, it is demonstrated the feasibility of the methodology here proposed to achieve difficult conditions for microbial and pathogens life, resulting in an effective disinfection of farmlands.