Probe for Windows: Scheduling whole season

Predictions about soil moisture requirements for the remainder of the season area are calculated

The predictions are only done if 'season scheduling' is chosen on ProbeMenu/Update or ReadingsMenu/Scheduling.

ProbeMenu/Update allows the data to be saved to the database for reports or export to MS.Access.

Example

The calculations are done in 1-day increments.

The value of RZ1 is calculated from...

RZ1 = Previous_RZ1 + ApplicationRate + Rain - CropWaterUse (DWU)

RZ1 is the total amount of water (mm) in the active root zone.

Application Rate is the effective amount of irrigation applied (mm) per day.

Rain is the effective amount of rain (mm) in the day.

Crop Water Use is the amount of water used by the crop, per day.

Losses from through-drainage, surface run-off and evaporation are the differences between delivered and effective amounts.


If RZ1 after a rainfall is above the full point it is cut back to the full point; the excess is excluded in the calculation of total effective rain.

Non-drip sites
Drip sites

Crop water use

Crop water use (DWU) = Evaluate(SiteDWUFormua) * K-Soil Correction

Site DWU Formula

K Soil Correction

Adjusts DWU depending on the current value of RZ1 relative to FULL and REFILL.

1 = FULL; 0 = REFILL; -0.1 = 10% of (FULL - REFILL) below refill.

Adjustment factor and constant assumed to be dependant on soil type, so the correction factors are saved in a 'KS' file.

e.g. the file SAND.KS (below)

    ------------------------
  Relative, Factor, Constant
       1.0,    3.0,        0
       0.0,    1.0,        0
      -0.1,    0.8,        0
      -0.2,    0.0,        1
    ------------------------

Will adjust the value of dwu depending on the value of soil moisture relative to FULL and REFILL...

RZ1 below..and above..Corrected DWU
FULLDWU = 3*DWU (through-drainage)
FULLREFILLDWU = DWU (normal)
REFILL10% below REFILLDWU = 0.8 * DWU (some stress)
10% below REFILL20% below REFILLDWU = 1 mm/day (high stress)

A KS file can also be used to allow for through-drainage when RZ1 is above FULL.

Lower and Upper limits

The Upper and Lower limits are the required maximum and minimum values of RZ1.

Rain

Predicted rainfall scenarios can be used.

GD Note: 'Scenarios' saved in PRWIN2.INI; rainfall data in 'RA' or weather file.

Total amounts required for whole season

The effective amount required at each irrigation is calculated as above

Totals for the season are calculated and saved in table SCHEDULE

The required delivered amount = EffectiveAmount * FACTOR4 (to allow for losses in system)

Total volume required (kl) is calculated from TotalDelivered * Wet Area

Wet Area = Area * ( RowSpace / WetWidth )

The calculated crop water use, corrected for K-Soil, is totalled and saved.

Fields in table SCHEDULE - available for GPT, SPT or RPT formulas.

FieldDescription
SeasonIDIdentifier for season (join to YEARS.ID)
SiteIDIdentifier for site (join to SITES.SITE)
RainScenarioIDIdentifier for rainfall scenario.
SEFFIRRITotal mm that will be effective.
SDELIVIRRITotal mm required to be delivered.
SNUMIRRISTotal number of irrigations.
STOTALVOLUMETotal volume required in Kl (mm * WetArea).
SEFFRAINTotal effective rain (delivered less wastage from over full point)
SDELIVRAINTotal rain from scenario (less amounts below lower limit)
SNUMRAINSTotal number of rainfalls used in scenario.
STOTALDWUCumulative total crop daily water use.

MS Access can be used to generate summary reports across all farms in a region

Details about each individual gain (irrigation) is saved in table SCHDETAIL. These fields are not available in Prwin, but can be used in Access to re-create the season simulation.

FieldDescription
SeasonIDIdentifier for season.
SiteIDIdentifier for site.
RainScenarioIDIdentifier for rainfall scenario.
DATEDate of gain
GAINTYPE2=Irrigation' 3=Rain; 4= EndOfDripPeriod; 15=EndofSeason
EffectiveAmountEffective gain (mm)
DeliverAmountAmount that should be delivered (mm)
UpperAmountCalculated value of Upper formula
LowerAmountCalculated value of Lower formula
DWUCalculated value of crop water use
KSKSoil correction factor used
LowestRZ1Value of RZ1 just before the gain
HighestRZ1Value of RZ1 just after the gain

Predicting next irrigation

The next irrigation is calculated with various options

RDI Factor

Only used to correct the DWU used to predict the next irrigation, but not subsequent irrigations.

e.g. Amount required = DWU * Evaluate(RDIFactor) * 7.