Irrigation

The APSIM irrigate module allows the user to:-¶

• specify irrigation schedules spanning multiple years
• configure an automatic irrigation schedule calculated on soil moisture
• specify both schedules to be turned on or off at any time in a simulation
• apply solutes in irrigation water for redistribution via the water balance module.
  
  

  Resetting Schedules¶

  Manual and automatic schedules can be enabled and disabled within a simulation via the message system. The syntax of a standard manager message to turn off the manual irrigation schedule would be as follows: irrigation set manual_irrigation = off Other related data is unaffected by this switch resetting and so, for example, the automatic irrigation scheduling can be set on and off for set windows in time using a pair of if statements in the manager file. Parameters for the automatic irrigation calculations can be reset similarly: irrigation set crit_fr_asw = 0.9 (0-1) irrigation set asw_depth = 150 (mm)

  Working with Irrigation Allocation Budgets¶

  The following example shows how the allocation mechanisms are utilized in the APSIM Irrigate module. Note that only automatic irrigation scheduling and remote scheduling (eg via the manager or operatns modules) is taken into account. The mechanism cannot be used in conjunction with a manual irrigation schedule. The example shows an annual allocation set on the first of July each year, which is applied using automatic irrigation scheduling. user_data_group.irrigate .parameters automatic_irrigation = on (on/off) ! switch schedule on or off crit_fr_asw = 0.66 (0-1) ! critical fraction of ! available soil water ! to trigger irrigation asw_depth = 600 (mm) ! depth for available ! soil water calculations user_data_group.manager .start_of_day if today = date('1_jul') then irrigation set allocation = 1000 (mm) endif

  Working with Irrigation Efficiency¶

  The following example shows how the irrigation efficiency is utilized in the APSIM Irrigate module. The example shows an irrigation_efficiency setting of 75%. This means that only 75% of the irrigation is actually being applied due to approximated losses due to evaporation, wind loss or runoff. user_data_group.manager .start_of_day irrigation.irrigation_efficiency = 0.75 if today = date('1_jul') then irrigation apply amount = 50 endif

  Using Default Solute Concentrations¶

  Default solute concentrations can be specified by a new "getable" parameter(s) called 'default_XXX_conc' , where XXX is the solute name. The units are ppm, and the parameter(s) is read from the parameter file. Note that solutes are not registered in the system simply by defining default concentrations. If you want to track these solutes through the soil, for example, they must be registered elsewhere to trigger a New_Solute Event, for example in the "solute_names = " line in SOLUTE, or by a number of other modules. When an irrigation is triggered (from MANAGER or from the parameter file) and no specific information on solutes in the irrigation is supplied, then the default solute concentrations will be used if they are supplied. Any specific information however will over-ride the defaults. If specific information is provided, then details of all the solutes must be given, because no defaults will be used. A parameter file example is given below: sample.irrigate.parameters default_cl_conc = 100.0 default_br_conc = 50.0 sample.solute.parameters solute_names = cl br cl = 0 0 0 0 0 0 0 (kg/ha) br = 0 0 0 0 0 0 0 (kg/ha) The reportable variable is "irrigation_XXX" where XXX is the solute name. The units are kg/ha.

  Using APSIM Irrigate with APSIM WaterStorage¶

  There is an option to use APSIM Irrigate in conjunction with the APSIM WaterStorage module. Please also read the documentation for APSIM WaterStorage. APSIM Irrigate works on a ‘mm' basis, whereas APSIM WaterStorage works on real volumes (Ml). Hence, when an irrigation application is specified in mm, an ‘area of application' must be provided in order to calculate the required volume of water from the specified source instance of WaterStorage. As mentioned previously, whenever WaterStorage is used in a simulation for supply of irrigation water, a variable called ‘crop_area' (ha) must be specified in the manager logic. Irrigations using water from WaterStorage can only be initiated by using the ‘irrigation apply' action in manager. A new optional argument called ‘source' is added to the ‘apply' command line to trigger the use of water from WaterStorage. The required syntax is as follows: sample.manager.start_of_day if day = 10 then irrigation apply amount=10 (mm), source = dam bore dam2 () endif The argument ‘source' specifies the sources from which to obtain the irrigation water, in preferential order. In other words, in the above example, if the dam cannot fully supply the required water, the balance will be taken from the bore. If there is still a shortage of water, then dam2 will be asked next to supply water. There is no limit to the number of sources which can be specified. When the irrigation water is applied to the soil, it will carry the solutes makeup of the water source being used. Irrigation Module Outputs The Irrigation module outputs the following variables.
  
  

  Variable Name	Description
  irrigation	Total amount of irrigation added to profile during any timestep (mm)
  manual_irrigation	Current state of the fixed irrigation schedule (on/off)
  automatic_irrigation	Current state of the automatic irrigation schedule (on/off)
  crit_fr_asw	Critical fraction of available soil water (ie. above a 15 bar lower limit) below which irrigation is automatically applied. (0-1)
  asw_depth	Depth to which available soil water fraction is calculated. (mm)
  allocation	Current amount of irrigation allocation available for use (mm)
  allocation_ml	Current amount of irrigation allocation available for use (ML)
  carry_over	Amount of irrigation allocation unused as at reset of allocation (mm) (Value will be zero for days on which allocation is not reset)
  carry_over_ml	Amount of irrigation allocation unused as at reset of allocation (ML)
  irr_fasw	Fraction of available soil water within the critical irrigation soil depth
  irr_deficit	Deficit of soil water within the critical irrigation soil depth (mm)
  irrig_loss	Losses resulting from and application of irrigation in conjunction with the irrigation_efficiency mechanism.
  irrig_tot	Total irrigation specified, not including losses due to irrigation efficiency (mm)
  irrigation_XXX	Applied quantity of solute XXX, (kg/ha)