The irrigation system describes the type of irrigator, the application method (what triggers an application and depth applied) and where irrigation occurs.
The following diagram depicts what parts of the model the irrigation information entered in OverseerFM impacts. For a full interactive view of the scientific model in its entirety please click here
The irrigator types influence the amount of water lost and the defaults for return period and application depth. The applications and method is used to model the water applied and hence nutrients in the soil, soil moisture, drainage and therefore leaching of nutrients.
- Irrigation must align with the climate used in the analysis, i.e. the irrigation that would be applied based on typical climate (over last 30 years). The model will determine the amount of water applied based on the method used to monitor soil moisture.
- Entering application depth is not recommended as it is unlikely to align with climate information.
- Physical irrigation systems with the same management characteristics can be set up as a single system to make it easier to manage.
- Scheduling methods and timing can be entered on a block by block basis.
- Default nutrients should be used unless it is known to differ as a long-term average.
OverseerFM supports seven irrigation systems (fixed pivot, spray lines, border dyke, controlled flood, micro irrigation, travelling and solid set). The type of irrigator has an impact of atmospheric and drainage losses and the defaults for application depth and trigger points. An irrigation system may define one of more physical irrigators that are all the same type and have the same management approach.
A block may have up to two irrigation systems applied. The percentage of the block must be entered for each system.
The irrigated area may be drawn on a map. Overseer will use the irrigated area and block drawings to select the percentage of blocks being irrigated.
Blocks are broken down by irrigator and soil when the model is run, and the results combined into an overall block result. Soil/irrigation results can be seen under the block details or farm details reports.
Overseer does not know the percentage irrigated of each soil, it simply divides the soils evenly and so if there is a significant difference in soil composition that should be modeled separately this should be created as a separate block.
Applications are described monthly and define the method used to assess soil moisture levels and hence the irrigation required.
From this the model determines the amount of water applied daily, which is then rolled up to monthly values.
The type of irrigator influences GHG from electricity and default values for return period, trigger points, minimum and maximum depth.
In pastoral systems, irrigation increases pasture production and hence animal production. This leads to higher N intake by stock and hence higher amounts of N excreta as urine. It is important that this increased pasture growth is recognised in the model by adjusting relative yield in the animal distribution screen.
Irrigation is significantly impacted by variations in weather. The climate used in Overseer is a 30-year average and so it is important that irrigation is consistent and aligns with the climate used in the model. This may not be the actual water applied in the year being analysed because that would be dependent on weather, but rather what would be applied if the climate was as set and the approach to monitoring soil moisture, triggering events and determining depth was applied. For example, if you are trying to model the farm’s practice during a dry autumn when irrigation events might go on for longer than normal. If the farm would not normally irrigate during, say, April and May, then those irrigation events should be left out of the modeled scenarios.
If you are adjusting the depth and return period of applications to meet a certain amount of water applied, then it will make it more difficult to make year on year comparison of farm management changes.