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The IQQM CropMod2 replicates the water requirements for a cropped area. This is a process-based model which allows you simulate a farmer’s decision on the area to plant in each season and evapotranspiration of the different crop types, and generates a demand based on the maintenance of a target soil moisture level. You can also simulate rice irrigation by specifying ponding behaviour and return flows.

Configuring generic crop settings

Before configuring an IQQM CropMod2 Demand model on a Water User node, you must specify crop factors for the entire scenario using Edit

» Crop Parameters.... Crop factors defined in this way are accessible for each water user node.

The method for defining crop factors is based on FAO 56 which divides the growth period of every crop into four developmental stages based generally on water requirements. These stages are:

• Initial (or establishment) stage - occurs between planting and when there is approximately 10% ground cover. Water requirements are quite low and constant;
• Crop development (or vegetative) stage - sees a rapid increase in the amount of water required by the crop until there is generally about 70% to 80% ground cover and maximum rooting depth is achieved;
• Mid-season (or flowering) stage - requires the maximum amount of water in the life of the crop; and
• Late (or yield and/or ripening) stage - there is an approximate halving of water requirement as the crop ripens, reaches maturity and is harvested.

TheConfigure Crop Parameters window (Figure

1)

 and the parameters required for each crop type are described in Table

1.

Figure 1. Configure Crop Parameters

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Figure 2. Crop factor Editor

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Planted Area tab

This tab (

Figure 3) broadly defines the area to be used and the proportions between the primary and secondary crops. The parameters that must be defined are described in Table

2. The Primary crop planting decision date refers to the day when the water user decides the area of crop(s) to plant in the primary season. This should be before the Start Date of any specified primary crop, otherwise the area initially planted will be based on the primary crop decision from the previous year. The start date of the crop is specified in the

Crop mix tab. Similarly, the

Secondary crop planting decision date is the day when the water user decides the area of crop(s) to plant in the secondary season. As per the primary season, this should be before the Start Date of any specified secondary crops.

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Soil tab

This tab (

Figure 4) defines soil inputs. There are individual stores for each crop type. Areas that are not being cropped are referred to as fallow, and are simulated using two soil layers. Fallow area occurs between cropping seasons or during the irrigation season if the maximum developed area is not planted. At the end of a cropping season, the soil moisture of the crop area and fallow areas are merged. Table

3 provides a description of the parameters. Refer to the Source Scientific Reference Guide for more information.

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Climate tab

This tab defines four parameters (Table

4) for climatic data.

You can specify four parameters for rainfall data in the Rain data tab (

Figure 5 & Table

5).

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Risk tab

At the start of an irrigation season, each water user node decides on how much area is to be planted (and thus irrigated). This is determined by the Decision Date for the primary and secondary season. This calculation uses a relationship referred to as the farmer’s risk function. In the IQQM crop model, farmer’s risk is modelled in two different ways: an area-based approach and a volume-based one. For the former, the function relates available resource to planted area. For the latter, the function relates current the available resource to expected available resource. The expected available resource is then divided by the calculated average crop requirement to determine the planted area. Refer to the Source Scientific Reference Guide for more information.

For both area and volume based risk functions, you must specify the wet, average and dry periods. The model interpolates between these values based on an index of current conditions. For the area based method, the model automatically calculates the index based on soil moisture. For the volume based method, the index is calculated based on the defined inflow data as follows:

• Inflow time series - Load the time series data if the risk function type is volume (

• Figure 6); or
• Median prior 6-Monthly Inflow - Long term average inflows are entered as a monthly pattern. The volume based risk function uses an inflow index based on the supplied time series data. The index compares the total inflow from the time series file in the preceding 183 day period to the long term average for the same period.

Selecting the risk function type, and then clicking on either the Primary Crop or Secondary Crop button opens the Farmers Risk dialog (Figure

7).

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Figure 7. Farmers' risk functions

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Efficiency tab

This describes a number of parameters that can result in the water requirement being scaled up (

Figure 8). Additional extractions are required if there is a practice of applying excess irrigation, with the excess being captured and returned to the water user storage. Additional extractions are also required if losses occur prior to delivery of extractions to the crop. The water user efficiency tab then allows these values to be scaled down. The default crop configuration values are zero, and hence if not defined, changing the water user efficiency parameters will have no effect.

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The parameters are:

• Irrigation return factor - Allows you to scale the on farm return factor defined through crop configuration. These two parameters combined, result in an increase in the volume ordered with the additional volume being available for returning to the water user storage;
• On farm loss factor - Allows you to scale the on farm loss factor defined through crop configuration. On-farm loss represents the percentage of water that is diverted from the river and passes the irrigators meter, but doesn’t make it to the cropped area and doesn’t reappear at any other point. An on farm loss will result in the volume ordered being increased and is applied after the irrigation return factor; and
• On farm escape factor - Allows you to scale the on farm escape factor defined through crop configuration. On-farm escape represents the percentage of diversions that is lost prior to being applied to crops however this flow returns to the river system at a confluence node. An on farm escape will result in the volume ordered being increased and is applied after the irrigation return factor and the on farm loss factor.

Return flow tab

Return drainage water is surplus drainage water from irrigation or from rainfall runoff. This water can be redirected into the on farm storage or otherwise can be returned to the river via a confluence node. This is shown in

Figure 9. The various parameters are shown in Table

6.

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Crop mix tab

This tab (Figure 10) defines the proportions and timings of different crops planted in the defined area.

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