Ineffective filtration systems are a bugbear of many spray irrigators because they block easily, preventing the valuable nutrients in effluent from reaching the soil.
Tinamba dairy farmer Tom Gannon trialled a self-cleaning effluent pump on a pontoon in his effluent pond, to increase the effectiveness of dairy effluent application through a pivot irrigator.
Tom hoped the self-cleaning pump would result in less time spent cleaning the filtration system and more effluent flowing through the pivot irrigator onto his pastures.
Because his farm is on a floodplain of the Macalister River, he also wants to reduce the risk of run-off when he applies fertiliser to his paddocks.
In particular, Tom wants to minimise the risk of effluent impacting the surrounding environment during high rainfall events, and regularly fertigating from the two effluent ponds located near the dairy.
Tom and Melanie Gannon milk 500 cows twice a day, off 500 acres, 90 per cent pivot irrigated and 10 per cent flood irrigated.
Investing in pivot irrigators has enabled more efficient use of the effluent water as fertigation — and this has led to improved pasture growth, with up to 10 per cent more production.
“The main challenges with irrigating effluent through the pivot irrigation system is blockages of the filter,” Tom said to a group of farmers at an open day on his farm.
Fine grass particles from manure washed from the dairy yard into the effluent pond tended to block the filtration system on the pump that moved liquid to the pivots.
This caused a pressure drop at the pump of 20 PSI after 10 minutes of irrigating. This lowered the supply pressure for the centre pivots and they operated at lower pressure than they are designed for.
The effluent blockages also had a flow-on effect in the pivot sprinklers, negatively affecting irrigation uniformity in the paddock.
“The sticking point was the filtration — the filter would actually block up a lot,” Tom said.
“I had to pull it apart all the time and it was a frustrating job.
“With flood irrigation, the fine grass particles aren’t a problem. But with switching over to pivot irrigators, it became a problem.
“The filter needs to protect the pivot sprinklers from blocking up with these fine particles.”
Tom invested in an inline filter for the effluent pond pump that automatically filters, brushes and backflushes as grass particles build up.
Initial results filtering grass particles were good, but sediment build up on the filter led to a return to the previous regime, where Tom had to manually clean the system before he could irrigate.
With time at a premium, this meant he wasn’t fertigating as often as he wanted to. The blockages in the pivot sprinklers also affected how much he was able to use clean irrigation water.
This had a flow-on effect to pasture growth and production.
The second plan was to install a rotating self-cleaning pontoon and brush that minimises the amount of dirt and manure that leaves the effluent pond as fertigation.
Very fine mesh stopped grass particles entering the suction line. Because the self-cleaning filter rotated, this action prevented solids from sticking to the mesh – they return to the effluent pond.
A jet of water helps to clean the filter.
Blockages and pressure drops have significantly reduced, and fertigation is now able to be applied regularly to about 80 acres of the farm.
“What I hoped to see through this project, is more effluent going through the pivots, going onto the pasture and growing more grass,” Tom said.
“Effluent is important to get nutrients back into the soil that you’ve already harvested off, from the cows grazing pasture and turning that into milk in the vat.
“But it’s also important with the way we put effluent onto the paddock, so it doesn’t enter the waterway.
“I can rely on the system to put the effluent on the paddocks, and not have to worry about it getting into any waterways, particularly in high rainfall events.
“It also needs to save me time against how often I have to clean the filter.”
An assessment in March 2024 of pivot application and uniformity showed the pivots were running at correct pressure and the area under irrigation had improved by 22 per cent.
“I’m irrigating more, growing more grass and we’ve increased the number of cows we’re milking while maintaining the same stocking rate,” Tom said.
Tom is also using a muck spreader to spread solids on his paddock a couple of times a year, to reduce the build-up in the solids pond. That helped improve flow of liquids and reduce solids moving between the two effluent dams.
The project was part-funded by the Victorian Government’s Sustainable Irrigation Program, and administered through Agriculture Victoria and West Gippsland Catchment Management Authority.
“We’re partnering with irrigators to help tackle some the region’s greatest challenges like maximising water use efficiency and improving nutrient management,” said Anthony Good, land programs coordinator with West Gippsland CMA.
“These farmers are paving the way for sustainable irrigation by trialling technology that we hope will lead to better on-farm productivity, improved water quality in waterways and less greenhouse emissions from irrigated agriculture.”