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This is used to define parameters specifically related to the crop to be planted. To add a new crop, right click Irrigator and choose Add Crop Type. Figure 4 5 shows an example of a crop, named Wheat, that has been added to the model. Consult the Source Scientific Reference Guide for greater detail regarding parameters for the following sections.
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5. Irrigator demand model (General and Soil Configurations)
Soil Configuration
Crop specific soil factors can be defined on the same page as General Configuration - see Figure 45. Soil moisture capacity is specified at the district level and this is assumed constant for all crops in the district. The Depth of the Root Zone, Depletion Factor and Initial Depletion are specified for each crop.
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| Note: Irrigator allows more flexible representations of crop based planting decisions than earlier crop demand models, which better align with economic modelling. If the planted area is defined using the Function Editor, then other factors such as economics can be considered. In addition, planting decisions can be reviewed periodically during the season. This allows decisions to be made to cut back the irrigated area, reduce irrigation intensity or potentially trade water if there is insufficient water to finish the crop. |
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6. Irrigator demand model (Planting Decision, Fixed Area)
If Lookup Table is choosen as the Decision Type, you must define a configuration table (as shown in Figure 7), which can be entered manually or imported using the Import button. This table is used to determine the Area and Underirrigation Factor for a given value of Available Water. Additionally, for values of Available Water that are not present in the table, linear interpolation is used to determine the other two parameters. For the example shown in Figure 7, if available resources in a RAS are 15000ML, the planting area will be 3000ML based on linear interpolation between (10000, 2000) and (20000, 4000). The available resources from water user (order debit type) is determined from the current account balances plus released water in the river plus on farm storage available water.
Figure 7. Irrigation demand model (Planting Decision
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, Lookup Table)
Target soil depletion
The amount of water in the rootzone is defined in terms of rootzone depletion, which describes the soil water deficit of the rootzone relative to field capacity. The target depletion can be specified as a time series, a pattern or as an expression.
Two target depletions can be specified (as shown in Figure 46):
- A Regulated Target - the target at which Irrigators water and attempts to maintain soil depletion; or
- An Opportunistic Target - used to generate opportunistic requests.
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You can configure some simple economic considerations in Irrigator, as shown in Figure 8. To enable economic values to be configured for a crop, right click on the crop and choose Enable Economics. A simple, linear crop water production function is used to predict the reduction in crop yield resulting from water stress. Irrigator records the relative yield as a daily time series. The following parameters must be specified as an expression:
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For more information consult the Irrigator Demand Model page of the Source Scientific Reference Guide.
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8 - Irrigation demand model (Crop Economics)
Runoff
The supply escape efficiency defines the amount of applied irrigation water that becomes runoff. A value of 0 results in no irrigation runoff; 10% indicates that 10% of the applied irrigation water becomes runoff. You must also specify a return efficiency, which means that the proportion of runoff that is returned to the water user can be stored in the farm storage or returned to the river. By default, both are set to 0 and do not need to be configured.
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This specifies the percentage of applied irrigation and rainfall that becomes deep percolation and drains below the rootzone. A 10% supply escape efficiency would indicate that 10% of the applied water becomes runoff. The return efficiency is not configurable for deep percolation.
Results of Irrigation demand
After configuring and running the scenario, you can view the results of the demand model. Figure shows the results how the water stress coefficient (Ks) varies over time. For soil water limiting conditions, Ks < 1. Where there is no soil water stress, Ks = 1.
The higher the value of Ks, the healthier the plant.
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| Note: A crop dies when Ks is less than 0.5%. |