SOIL-TEMPERATURE UNDER DIFFERENT SURFACE MANAGEMENTS - TESTING A SIMULATION-MODEL

Conservation tillage is known to change the temperature and water cont ent of the soils on which it is practised, largely through its effect upon crop residue cover and consequently upon energy exchange between the atmosphere and the soil surface. If simulation models are to be us ed to estimate these changes, then the processes by which temperature and water content are controlled must be explicitly represented using basic theories of energy and water transfer. A simulation model was co nstructed to represent processes of energy and water transfer among th e atmosphere, plant canopies, surface residues, and soil. Estimation o f energy and water transfer from hourly meteorological data and basic plant and soil properties allowed the model to reproduce a delay of ab out 1 week in soil warming and drying under reduced vs. conventional t illage during March and April in central Alberta. Estimation of these transfers also allowed the model to reproduce soil temperatures that w ere as much as 10 degrees C cooler under grass vs. fallow during June and July. The hourly behavior of the model was found to be consistent with diurnal trends in water and energy transfer observed elsewhere. C ovariance analyses indicated that 50-60% of differences in soil temper atures measured under different surface covers were reproduced by the model. These results support the hypothesis that differences in soil t emperatures under different surface covers may be largely attributed t o the effects of surface cover on energy transfer between the atmosphe re and the soil surface.