Probe for Windows: Scheduling

The required irrigation for the next irrigatuion is calculated, and also for the remainder of the season.

The calculations are done in 1-day increments.

Each day the value of the water in root zone 1 (RZ1) is calculated from...

RZ1 = Previous_RZ1 + Application_Rate + Rain - Crop_Water_Use

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.
Crop_Water use = Evapotranspiration (ET) * Crop_factor (Kc) * Soil_Factor (Ks)

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.

Irrigatiions

1. Cyclic
   • Water is applied when the RZ1 falls to stress
   • Stress can be either Refill, or the varying Lower Limit
   • RZ1 back to the upper limit (normally FULL)
2. Continous
   • At the start of each 7 day period the amount required to reach the next 'Target' is calculated.
   • The target is (normally) the average of UPPER and LOWER limits.
   • Application rate is the daily effective delivered rate
   • The Rate is re-calculated every 7 days (DRIPDAYS).
   • TargetAmount = ( UPPERAMT + LOWERAMT ) / 2
   • Required effective amount = CropWaterUse * 7 + RZ1 - TargetAmount.
   • Assumed that the amount will then be delivered on a daily basis.

Crop Water Use, or ET

The crop water use used to calculate the next irrigation can be...

1. Probe
   Calculated rate-of-change of soil moisture. CDWU = PDWU
2. Estimated
   Calculated from the site formula when readings are posted, but may be changed.
   If it has been changed, the value will be used up to the first irrigation. CDWU = PDWU
   If it has not been changed, the ET will be re-calculated each day. CDWU = ET * Kc * Kc
3. Historical
   ET calculated each day using the site formula. CDWU = SiteFormula * Kc * Kc
4. Crop
   ET calculated each day using the Crop formula. CDWU = CropFormula * Kc * Kc
5. Keydata
   ET calculated each day from a keydata row formula. CDWU = ET * Kc * Kc
6. Forecast
   ET from a forecast weather service, or other weather data. CDWU = ET * Kc * Kc

For the remainder of the season (after the next irrigation), ET is calculated from ...

• Probe, Estimated, Historical,Forecast: Site formula
• Crop: Crop formula
• Keydata: Keydata formula

Note: If there is no site formula the global DWU formula will be used.

Prediction calculations also use..

• Predicted rain: use (site-sepecific)
• Chop gains to Full point (site-sepecific)

Prediction Variables available for reports here

Amount of water that should be applied

• Cyclic
• Continuous
  • Amount required to reach target, total mm in 7 days
  • Target-Current + CDWU
  • Limited by max pumping rate

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

ET/DWU formulas

• Allows for variation as a function of date - dwu details
• Can also include both ET and canopy terms e.g. blenheim.et * shiraz.ca
• Can also be a function of soil moisture status relative to full/refill/pwp (but see k-Soil below).

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
	FULL	DWU = 3*DWU (through-drainage)
FULL	REFILL	DWU = DWU (normal)
REFILL	10% below REFILL	DWU = 0.8 * DWU (some stress)
10% below REFILL	20% below REFILL	DWU = 1 mm/day (high stress)

The .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.

• Allow for varying upper and lower limits to be entered as a function of date.
• Values can be specified in either...
  absolute mm relative to FULL or REFILL
  or relative to FULL and REFILL (or PWP).

Rain

Predicted rainfall scenarios can be used.

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

• Rainfalls 'senarios' are in files, with date and amount in mm.
• Actual weather station output files can be used.
• A 'Low' scenario could be generated by analysing rainfall records for the area, over many seasons, and selecting (or generating) a 'low probability' year.
• A 'minimum' amount can be specified.
• Predictions for different rainfall scenarios are saved separately in table 'SCHEDULE'.

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.

Field	Description
SeasonID	Identifier for season (join to YEARS.ID)
SiteID	Identifier for site (join to SITES.SITE)
RainScenarioID	Identifier for rainfall scenario.
SEFFIRRI	Total mm that will be effective.
SDELIVIRRI	Total mm required to be delivered.
SNUMIRRIS	Total number of irrigations.
STOTALVOLUME	Total volume required in Kl (mm * WetArea).
SEFFRAIN	Total effective rain (delivered less wastage from over full point)
SDELIVRAIN	Total rain from scenario (less amounts below lower limit)
SNUMRAINS	Total number of rainfalls used in scenario.
STOTALDWU	Cumulative 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.

Field	Description
SeasonID	Identifier for season.
SiteID	Identifier for site.
RainScenarioID	Identifier for rainfall scenario.
DATE	Date of gain
GAINTYPE	2=Irrigation' 3=Rain; 4= EndOfDripPeriod; 15=EndofSeason
EffectiveAmount	Effective gain (mm)
DeliverAmount	Amount that should be delivered (mm)
UpperAmount	Calculated value of Upper formula
LowerAmount	Calculated value of Lower formula
DWU	Calculated value of crop water use
KS	KSoil correction factor used
LowestRZ1	Value of RZ1 just before the gain
HighestRZ1	Value 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.

Drip: Calculation of Schedule Amount and Date

The schedule amount is the volume of water required to reach a target soil moisture in 7 days time The target soil moisture can be either tab: 'mode options'
• do nothing
• target = middle of Upper and Lower
• below lower: target= lower
  above upper: target= upper
  between lower and upper: do nothing
soil moisture depletion rate, or daily water use sm = crop et * crop.kc * soil.ks Crop et (tab: scheduling options)
• PDWU - use the actual, measured, rate of soil mositure depletion
  but if too low or too high can revert to a formula
  if calculating the rest of the season, use either EstDWU, or Historical DWU
• EstDWU - the value from the site 'historical formula', but the value can be changed by the user
• Historical - the value from the site formula, but the value can not be chaged by the user
• Crop - the value from a formula for the Crop - the value can not be changed by the user
• Keydata - the value from a formula entered in a keydata row
• Forecast - the average forecast et over the next 7 days - see Forecast
amount required = rise/fall to target, less predicted rain AmountRequired = Target - Current - ForecastRain application rate will be soil depletion rate - amountrequired/day rate need to apply water ApplicationRate = DecisionDWU + (AmountRequired) / (7 days) If ApplicationRate < 0 Then too wet ! DWU too low to dry out soil to reach target ! have to fall at dwu only, with zero delivered ApplicationRate = 0 If ApplicationRate > MaxApplicationRate pump cannot deliver ApplicationRate = MaxApplicationRate if 'chop to full' ON, the soil moisture will not be allowed to go above the full point (fiekld capacity) any additional water will be assumed to be lost to through-drainage or surface runoff calculate the rate RZ1 needs to fall/rise to hit target if in manual mode, 'fd_ScheduleAmount' is how much *will* be applied this needs reducing by factor2 to get 'effective gain in soil' AmountRequired = (ScheduleAmount / Factor2) - ForecastRain Final... .EffectiveAmount = RequiredAmount .DeliverAmount = RequiredAmount * Factor2 if DeliverAmount < Reasonable DeliverAmount = 0

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