The Study of Soil Temperature Variations and Thermal Diffusivity in Wet and Dry Seasons at Ibadan, Oyo State, Nigeria

Soil temperature is the temperature of the soil at different depths beneath the soil surface and does not only indicate climate change. Agricultural practices are strongly impacted by soil temperature making it a very important variable for soil conditions. Thermal diffusivity is the ratio of thermal conductivity to volumetric heat capacity. It tells how materials conduct thermal energy relative to how they store thermal energy. Soil temperature is strongly affected by thermal diffusivity. Therefore the purpose of this study is to investigate soil temperature variations and thermal diffusivity during the wet and dry seasons in Ibadan, Oyo State, Nigeria. Soil temperature data at depths of 5 cm, 10 cm, and 30 cm were obtained from the Nigeria Mesoscale Experiment (NIMEX) site for the period July to December 2006, covering both wet (July–September) and dry (October–December) seasons. Thermal diffusivity was estimated using the Horton numerical method. Results show clear seasonal and depth-dependent variations in soil temperature, with lower temperatures recorded during the wet season due to increased soil moisture and cloud cover, and higher temperatures during the dry season associated with reduced moisture and increased solar radiation. Temperature amplitude decreased with depth, indicating attenuation of surface thermal signals. Thermal diffusivity exhibited significant variability, with maximum values recorded in September and minimum (including negative) values also occurring within the wet season. The negative diffusivity values are attributed to rapid temporal temperature fluctuations linked to soil moisture dynamics and the sensitivity of the numerical method used. Overall, the study highlights the strong influence of seasonal climatic conditions and soil moisture on soil thermal regimes in tropical environments.