PREDICTING SOIL TEMPERATURE AND SOIL HEAT FLUX UNDER DIFFERENT TILLAGE-SURFACE RESIDUE CONDITIONS.

Model descriptions for soil temperature utilizing readily available information are needed to project management effects of tillage. In many cases these model descriptions must cover periods of a month or more during the growing season. A procedure was developed to utilize daily maximum and minimum air temperature along with normalized root zone temperatures. A Fourier series analysis of daily normalized soil temperatures averaged over part of a growing season showed that the average value around which average normalized soil-temperature curves (diurnal wave) oscillate varies with depth and season. Amplitudes and phase angles of the first two harmonics of the Fourier series were approximately the same for all treatments over four seasons. A model was developed to estimate soil temperatures for various tillage-residue cover treatments with and without a crop cover for the northern Corn Belt states.