An irrigation Water user has one or more irrigated fields. Each irrigated field consists of a sequence of crop shifts (a crop sequence). A crop shift is characterised by a starting date (sowing date), a crop, and a reference to the irrigation method that will be used to irrigate the crop. A crop shift lasts until the end of the last growth stage of the crop in the field.
In the Irrigated field section, the crop sequence for each field has to be specified.
Each row added to the Irrigated field tab represents one of the crops growing on the field in a particular period and on a specific area of the field. An irrigated field for a specific crop is defined by various properties, such as the name of the crop, the area of the field, the properties of the soil in the field and its ability to generate runoff.
The buttons at the bottom of the Irrigated field table can be used to add, or delete the input for the different irrigated fields of the water user node. A field is added to the Irrigated field node by clicking the ‘Append’ button ‘+’, which results in a line being added to the Irrigated fields table. To delete a field, select the field’s line and click Delete ‘-’: . The properties of the field can be edited directly in the table.
Some attributes of the field are visible on the row of the specific field in the field’s tab and they must be specified. These are:
· ID. The field identification code, ID, is automatically given every time a new field is added to the model.
· Name. This corresponds to the name of the selected crop grown in the field is entered.
· Priority. If ‘by priority’ has been selected as deficit distribution method in the Irrigation scheme section, priority is an integer defining the priority with which the different fields will receive water in condition of scarcity. The fields with the highest priority (lowest priority number) will receive the full demand first.
· Area. Size of field growing with specified crop.
· Min. cycle time. The so-called minimum cycle time, expressed in days, is an important parameter, if the farmer cannot irrigate the whole field within a single time step, but in multiple time steps. In this case, sections of the field will be created accordingly. Hence, soil moisture, and consequently yield, may be different on the different field sections and internally these are treated as different fields. In each output time step, the average field conditions are written to the result file. To disable the minimum cycle time, set it to a value less than the simulation time step. Example: If, for instance, it takes a farmer two days to irrigate the entire field and the time step of the simulation is one day, then the field is divided into two field sections and on the first day he irrigates one half and the next day the other half.
· Recycle crop sequence. If the same sequence of crops is cultivated in the field, this box should be ticked. The frequency with which the crop sequence is recycled depends on the total length of the crop sequence. If the sowing years of the different crops differ, the sequence is repeated as soon as the last crop is harvested and a new year starts.
· Soil and Runoff model. Here, the appropriate Soil and Runoff model for the crop of interest can be selected. By clicking on the box, the list of the available models appears. The available models are those entered in the section Irrigation data ® Soil and runoff.
When clicking on the arrow next to the field’s ID, the tab expands and more attributes of the field appear, which also have to be specified. These are:
· Crop model. The Crop model can be chosen from those entered in the section Irrigation data ® Crops (to jump to this section, right click on the specific crop’s line in the tab and select ‘Go to Crops’). To select the model, click on the Crop model field and the available option will appear.
· Sowing year. The first sowing year for the crop has to be specified.
· Irrigation method model. The Irrigation method can be selected from those entered in the section Irrigation data ® Irrigation method (to jump to this section, right click on the specific crop’s line in the tab and select ‘Go to Irrigation method’). The list of the available models appears when clicking on the Irrigation method model box.
· First sowing date. This field displays the date when the crop is sowed for the first time, given in dd-mm-yyyy format. This field cannot be edited.
· First harvest date. This field displays the date when the crop is harvested for the first time, given in dd-mm-yyyy format. If a crop is harvested before the next crop is planted, the model assumes that there are no crops at this field in the time between crops, and hence that the irrigation demand is zero. When the next crop is sowed the water content in the root zone will be reset to the initial water content, as specified in the soil water model. This field cannot be edited.