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
