Variation of temperature in the ground with time and depth from the surface is a natural phenomenon which affects most physical and chemical properties of soil. Records of soil temperature were obtained at five depths (2, 50, 100, 150, and 200 cm) below the surface of the earth at Akole, Abeokuta, between 1 January 2014 and 31 December 2014. The soil temperature varied from 27.75 degrees C at depth 200 cm to 29.9 degrees C at 2 cm. The diurnal temperature range for depths between 2 and 200 cm during the dry season was higher (about 18 degrees C) than that during the rainy season (about 12 degrees C). The temporal variation of ground temperature from the surface at different depths was analyzed by Fourier technique, and thermal diffusivity was computed using amplitude and phase angles of the first three harmonics of the annual thermal wave. The coefficients of soil temperature obtained by Fourier analysis depict the impartial description of the variation with depth of the soil temperature waves. Among the three harmonics calculated, the first harmonic described soil temperature variation to 95.07% while the first two harmonics described the variation to 98.72%. Further harmonics contribute insignificantly to the improvement of the variation. The annual damping depths of the study area calculated from the phase angle and amplitude angle and directly from daily average soil temperatures were 217.39, 227.27, and 217.90 cm, respectively. In the same vein, thermal diffusivity of the study area was found to be 5.1463 x 10(-7), 4.708 x 10(-7), and 4.7305 x 10(-7) m(2)/s, respectively. The annual amplitude, the mean wavelength, and the phase displacement at the surface were 2.68 cm, 14.0 m, and 31.38 days, respectively.
