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Navigation: Main Menu and Buttons > Model > MODFLOW Dialog Boxes > Farm Land Use Properties Dialog Box > MODFLOW-OWHM Version 2

Crop Leaching Requirement Pane

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This pane is on the Farm Land Use Properties dialog box.

CROP_MAX_LEACHING_REQUIREMENT

The crop leaching requirement is the fraction of total irrigation (applied) water that must pass through the soil to prevent the soil salinity from reaching the tolerance of the crop.

RHOADES Equation ==> ECw/(5*ECe - ECw)

CROP_LEACHING_REQUIREMENT and CROP_SALINITY_APPLIED_WATER read a NCROP LIST that may be one of the following input:

1.FLOAT ==> Specify its exact value or a formula.

2.RHOADES ==> Indicates that Rhoades equation is used

3.None ==> Indicates that evaluation is skipped (set to zero)

4.Custom Expression

If Custom Expression is selected, the user specifies any equation that has a set of Predefined Variables (See bottom of this file). Any scale factors that are loaded are applied to the result of the equation

Custom Expression supports keywords and in-line IF,structured as "IF[ Condition, TrueResult, FalseResult ]" where

Condition   is a conditional expression supported by OWHM

TrueResult  is the result that is returned in Cond is TRUE (may be an expression)

FalseResult is the result that is returned in Cond is FALSE (may be an expression)

Example Custom Expressions:

ECw/(5*ECe - ECw)         # <= Custom expression equivalent to RHOADS equation for calculating the Leaching Requirement (LR)

(ETi/DU)/(1-LR) - ETi     # <= Custom expression equivalent to RHOADS equation for calculating the Applied Water (AW)

IF[ ETc > ETr, (ECe/ECw)*LOG(CIR) + CIR, 0.1*CIR ]  #  <= Example of an in-line IF

A modified Formula Editor can be used to help set up the custom expressions.

Predefined Variables

LR      Leach requirement (-) ==> Set by CROP_LEACHING_REQUIREMENT

ECw     Electrical conductivity of irrigation water (dS/m)

ECe     Crop Electrical conductivity tolerance (dS/m)

CU      Potential consumptive use of crop (total potential consumption of water) (L3/T)

ETr     Reference EvapoTranspiration

ETc     Crop evapotranspiration from precipitation and irrigation (L3/T) --if irrigation is fully met

ETp     Crop evapotranspiration from precipitation (L3/T)

ETi     Crop evapotranspiration from irrigation (L3/T)

CIR     Crop irrigation requirement = ETi (water required to meet consumptive use - under perfect efficiency  --EFF=1)(L3/T)

DMD     Crop irrigation demand            (water required to meet consumptive use - includes efficiency of irrigation)(L3/T)

P       Precipitation that falls on crop (L3/T)

AREA    Crop area

Tgw     Transpiration from groundwater-root uptake

Tp      Transpiration from precipitation

Ti      Transpiration from irrigation

EFF     Irrigation efficiency

ROOT    Crop root depth

CapF    Capillary Fringe Depth/Length

DP_p    Deep percolation from precipitation

DP_i    Deep percolation from irrigation if irrigated demand is fully met (includes added demands, but not deep percolation from salinity irrigation).

DP      Total potential deep percolation from precipitation and irrigation

ADRS    Crop Added Demand Runoff Split (ADDED_DEMAND_RUNOFF_SPLIT)

ADMD    Sum of other Added Demands for the crop