Evaporative Cooling of Wet Soil Surface under Different Agricultural Land Use Systems

Laboratory evaporation studies were conducted to assess the roles of the various stages of evaporation on heat reduction from wet soil surfaces. Undisturbed soil columns from three different fields viz., cocoa (Theobroma cacao), oil palm (Elaies guineensis) and arable were collected from the 0-10 cm depth at the Plantations section of the Department of Crop and Soil Sciences, KNUST, Kumasi. The samples were initially saturated with water at an initial temperature of 65 o C. The soil columns were subjected to surface evaporation by placing them under a Sanyo (40 cm) dynamic wide desk oscillating fan. Evaporation and temperature readings were taken at 5 minutes interval for 1 hour. Two homogeneous soil columns were used as for reference tests (control). Evaporation analysis showed 1st and 2nd stages of evaporation with cumulative evaporation being proportional to the square root of time at the 2nd stage. Temperature decreased rapidly with increasing evaporation during the 1st stage of evaporation till the falling and slow rate stages, during which change in temperature was minimal and almost constant. A 1 mm increase in evaporation showed a decrease in mean temperature by 7.53 o C, 7.35 o C and 7.10 o C from cocoa, oil palm and arable fields, respectively at 1% significant level. The results of this study indicated that under a constant atmospheric evaporativity, 1 mm increase in evaporation would cause a significant decrease in soil temperature.