Pastoralists seeking to maximise yields and quality from irrigated pastures have discovered that the use of technology to assist with decision making is essential to optimise profitability.
The WA Department of Primary Industries and Regional Development has been working with several stations in the Pilbara and Kimberley that have recently installed drip or centre pivot irrigation systems to understand plant water use under irrigation in the rangelands.
The department presented some of the learnings and observations at recent field days at Pardoo Station and Broome.
Development officer Chris Ham said one of the key findings was that monitoring helped to determine different watering requirements for irrigated crops, which varied depending on the soil type, plant species and seasonal conditions.
Mr Ham said irrigation was a specialised business and required a 24-7, 365 day-a-year commitment to time and attention.
“Site selection is very important and understanding the soil type, as there is significant variation in most soils and their subsequent water holding capacity,” he said.
“The aim of irrigators is to ensure there is consistent moisture levels in the ‘readily available zone’, so plants can freely access it.
“The amount of water plants can access is also dependent upon the depth of their root systems, which varies according to the age of the plant and the species.”
Mr Ham said while irrigation systems are typically engineered to supply between 12 to 15 millimetres per 24 hours, an efficient watering strategy often extended for more than 24 hours.
“For example, if you had a 40-hectare centre pivot and were growing Rhodes grass pasture, the optimal application for deep rooted pasture is 18 to 20 millimetres per irrigation, which might take up to 40 hours,” he said.
“One larger irrigation is more efficient than two lighter irrigations of 10mm each because you only wet the surface once, minimising evaporative losses from the canopy and soil surface.
“However, sometimes smaller irrigations are preferred to manage fertiliser applications or for young emerging plants and when conducting field operations like making hay or silage.”
Mr Ham said the department was also working on management strategies to match irrigation to plant growth cycles and seasonal conditions to avoid over or under watering.
“Sometimes a ‘green drought’ occurs when crop is green but is not growing to its potential due to a lack of appropriate moisture,” he said.
“Judging when to start watering after the wet season is also really important and when the weather changes quickly, particularly during the build-up before the wet season.”
Mr Ham said successful irrigation in the rangelands required consistent management decisions, backed by record keeping and data from soil moisture probes.
“It is preferable to use soil moisture probes on-site coupled with data derived from satellites, such as the Irrisat website, or engage a consultant who can offer tailored services to manage irrigation enterprises,” he said.
Mr Ham said irrigation management could be tricky and confusing and encouraged pastoralists to prepare, plan and ask for help.
“Irrigation is a big investment and management decision making and timing is critical to achieve high production so the department tries to support irrigators to ensure they get a suitable return on investment and use a valuable natural resource efficiently,” he said.
Source: WA DPIRD