The paper presents a method, a theory, and a measurement-control system permitting the control of the thermal and moisture conditions in the soil on the basis of measured basic physical properties of the soil and its thermal characteristics determined according to the method and theory presented herein. The characteristics of thermal diffusivity of soil in the function of moisture and soil density are of fundamental importance in the control of the thermal and moisture relations in the soil. Practical utilization of such characteristics allows soil moisture control at various soil densities so as to maintain optimum, for plant growth, thermal-moisture-air relations in the soil and in the ground layer of the atmosphere. The method and the measurement-control system presented here create the foundations for rational utilization of water and thermal energy in the atmosphereplant-soil system.