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Garden with Insight v1.0 Help: Soil patch next day functions: calculate actual soil evaporation

The calculation of actual soil evaporation from potential plant transpiration goes as follows. First the potential amount is reduced for the amount of soil cover using the soil cover index.

Then the estimate is reduced again to account for potential plant transpiration. Since potential soil evaporation was calculated before potential plant transpiration, the simulation may have artificially given more strength to soil evaporation than to plant transpiration. Plant transpiration has a greater pulling power on soil water than does evaporation from the surface of the soil because plant leaves usually have a greater combined surface area than does the surface of the soil. So the simulation reduces soil evaporation if potential plant transpiration is high.

The final estimate of soil evaporation is made by considering all soil layers down to the plow depth (usually 0.2 meters, or about eight inches). It is assumed that soil evaporation only occurs down to the plow depth. Considerations in determining evaporation are the wilting point and field capacity of each soil layer involved and the amount of water in each layer. The depth of a soil layer has an effect on its evaporation because water vapor moving up from lower soil layers has to move through the pore spaces in the layers above and is slowed down. Reduction of soil evaporation by depth works using an S curve whose shape is determined by parameters.

calculation of potential soil evaporation, soil cover index, potential plant transpiration
EPIC Evapotranspiration
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Updated: May 4, 1998. Questions/comments on site to
Copyright © 1998 Paul D. Fernhout & Cynthia F. Kurtz.