PREDICTING DIURNAL TEMPERATURE REGIME OF A TROPICAL SOIL

Abstract

We developed a numerical solution of the heat flow equation, based on the Crank-Nicolson approximation, and compared the computed soil temperature profiles for an Alfisol with those estimated by the model of Hanks et al. (1971), Fourier series solution, and the experimentally measured data. In a bare soil surface, the maximum temperature at the 5-centimeter depth estimated by the numerical solution and Hanks' model was 2.6°C higher, and by Fourier solution was 2.0°C higher than the observed values. Apart from the differences in the maxima, the predicted temperature profiles by the numerical method were similar to those observed. The Fourier method was a better predictor than the numerical method for subsoil layers. In straw-mulched soil surfaces with less amplitude, the predicted (by all three methods) and experimental temperature profiles were almost identical. The temperature prediction by the present numerical solution under maize (Zea mays) and cowpea (Vigna unguiculata) at the 20-cm depth was within ±0.6 and 0.4°C for a sunny and a cloudy day, respectively. The temperature profiles under maize and cowpea were related to the canopy cover. In a bare ridged soil, temperature was predicted within 3 to 6°C for the 5− and 17-cm depths and within 1 to 1.7°C for a soil mulched with transparent polyethylene sheet.