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

Conservation tillage is known to change the temperature and water content 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 used 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 constructed to represent processes of energy and water transfer among the atmosphere, plant canopies, surface residues, and soil. Estimation of energy and water transfer from hourly meteorological data and basic plant and soil properties allowed the model to reproduce a delay of about 1 week in soil warming and drying under reduced vs. conventional tillage during March and April in central Alberta. Estimation of these transfers also allowed the model to reproduce soil temperatures that were 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. Covariance analyses indicated that 50-60% of differences in soil temperatures measured under different surface covers were reproduced by the model. These results support the hypothesis that differences in soil temperatures under different surface covers may be largely attributed to the effects of surface cover on energy transfer between the atmosphere and the soil surface.