Effect of Near-Earth Surface Temperature on Soil Temperature at 5 cm Depth

The research investigates the effects of ground surface temperature (air temperature) on soil temperature at a depth of 5 cm. The study covers a period of fourteen (14) months from May 2010 to June 2011 in Akure, Southwestern Nigeria. With the aid of an automatic weather station, temperature readings were taken at a depth of 5 cm below the soil surface at five (5) minute intervals daily. It was also observed that many analyses of soil temperature are based on the theories of heat flow and energy balance. The study reveals that surface temperature has a weak effect on soil temperature. The best correlation coefficient obtained for the study period is about 0.56 with a quadratic equation of order 2 at 5% significance level. This implies that air temperature cannot be solely used to predict soil temperature at a depth of 5 cm. A study of diurnal variation reveals that air temperature is usually higher than soil temperature during the day, and vice versa. The study also revealed that surface and soil temperatures are generally lower during the wet months when compared with the dry months. The wet season average daily temperatures are 23.42oC and 27.69oC for air and soil while the corresponding dry season values are 33.92oC and 30.91oC respectively. The results are recommended for agricultural purposes such as determination of soil and environmental conditions for crop production.