Center Pivot and Linear Irrigation
Converting to Overhead Irrigation Systems
By 2012 summer planting, the team from ‘Undebri’ on the Goodar Rd at Goondiwindi will have converted over 2,000 hectares of gravity irrigated country to pressurised overhead irrigation using both centre pivot irrigators and linear move irrigators. The conversion of this country started back in early 2009 when an initial Valley linear move irrigator was purchased through local agents Pivot Irrigation and Pumping along with a towable centre pivot.
The second stage of the conversion project has been completed with the assistance of the Federal Government’s ‘Water for the Future’ initiative and as part of the Queensland Healthy Headwaters Water Use Efficiency Project. The owners of Undebri have committed to returning a certain amount of allocation in return for funding of a proportion of Stage 2 development after completing an assessment of water use efficiency improvement when converting to overhead spray irrigation.
Endfeed - Stage 2
The large overhead irrigation systems were considered due to the ability of the systems to apply regular small applications allowing the managers at Undebri to precisely meet the crop water use requirements without waterlogging events and to also manage irrigation periods around rainfall events to ensure maximum benefit is received from any rain. The system suits a wide array of crop rotations and also allow for opportunity cropping when seasonal circumstances leave a little in the tank to pull off an occasional short cycle crop. This was the case in the wet summer of 2009-10 when a late season sunflower crop was grown.
An excellent relationship has developed between farm manager Jeff Carter and equipment supplier and project overseer Richard Gower from Pivot Irrigation and Pumping.
Sunflowers - Stage 1
Undebri has adopted some of the most advanced features and options available from Valley’s product line. Items like GPS positioning of machines, full Autopilot control panels, radio based telemetry back to the farm office and web based interface for controlling the systems when not in the office.
These options allow the irrigation manager to easily monitor the systems as well as configure the machines to stop water or vary their application rate over the run length.
The fields under the systems have all been planted to cotton for the 2011-12 season with the area planted under the laterals scaled back to allow a daily application rate of 14 mm per day over the irrigated area. Due to the timing of the development, beds and field work were being completed during the assembly and dry/wet commissioning of the machines - but with some extra planning all has run smoothly so far with pre-watering over some fertiliser beginning in late September.
Each system has been configured with running costs in mind with all the linears running Nelson D3000 static sprays on a one metre spacing running in a 'bubbler' mode to drop water directly into the furrows. The one metre spacing reduces the flow through the regulator and nozzle, reducing losses and controlling flow to each sprinkler head compared traditional two metre spacing and a sprinkler between every second row of cotton.
Running costs were also considered during the initial design process for each system with a large amount of 219 mm diameter pipeline used in each system to reduce pipeline friction loss. The 650 metre endfeed linears have a pipeline friction loss of less than 0.69Bar (or seven metres of pump head) and the 745 metre centrefeed systems having a pipeline friction loss of less than 0.44Bar (or 4.5 metres of pump head). This equates to the pumps needing to produce no more than 22 metres of head at the top of each ditch feed linear cart. Numbers are still being added up but fuel usage on these systems should be around the 35 litres per hour on systems capable of pumping 23–24 megs per day.
Span lengths were also closely inspected during the machine evaluation process and 49.1 metre spans have been used to allow a true 48 x 1 metre beds under the spans as well as allowing a full bed for each span drive unit to run on so that wheel tracks can be easily control-led and maintained. The 49.1 metre span also prevents any crop damage due to the tower structure running over the crops.
Originally published in The Australian Cotton Grower, December 2011—January 2012.