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

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

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.

- Daily application rate is zero.
- If RZ1 falls to the lower limit an irrigation is assumed to take place.
- Required effective amount = UPPERAMT - LOWERAMT.

- Application rate is the daily effective delivered rate
- Rate is re-calculated every 7 days (DRIPDAYS).
- At the end of each 7 day period the amount required to reach the next 'Target' is calculated.
- 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 (DWU) = Evaluate(SiteDWUFormua) * K-Soil Correction

- 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).

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) |

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

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).

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'.

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 |

The next irrigation is calculated with various options

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

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