Farm Soil Properties Dialog Box

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The Farm Soil Properties dialog box is used to specify properties of the soil that affect evapotranspiration. It is displayed by selecting Model|Farm Process|Farm Soils...

The first column in the table is the Soil ID which is set automatically. The Soil Name will be used to define a global variable that can be used in assigning the spatial distribution of the soils.

The modeler must also specify the thickness of the Capillary Fringe and the Soil-Type. If the Soil-Type is set to Silt, Sandy Loam, or Silty Clay, the remaining data for the soil will be set automatically by the Farm Process. If the Soil-Type is set to Other, the modeler must supply values for A-Coeff through E-Coeff. These are coefficients used to calculate the pressure head, |ψ|, using an iterative solution of the following equation.

equation defining pressure head.

In the equation DRZ and n are calcuated from the A-Coeff through E-Coeff using the following equations.

Formula for DRZ
Formula for n

Where Tpot = potential transpiration from precipitation per cell [L/T]·[L2] and TRZ = depth of total root zone [L]. More detail on the calculation of the pressure head can be found in Schmid and others (2006) starting on page 42.