Undercover agent delivers hidden water savings
The use of an anti-evaporative agent on dams over summer can save water while water reticulation increases grazing flexibility.
Benalla farmers David and Anna Stewart are convinced that using a silicon-based anti-evaporative agent on their dam prevented them from running out of water in 2010. This in conjunction with the development of a whole farm plan and the reticulation of water to where it is needed has provided them with much improved water security.
The couple who run a small prime lamb enterprise on 100ha, applied the product in January after they realised the water in the main dam was "disappearing at an alarming rate". They continued to apply it every 10 days until the end of autumn.
At first David doubted that the product, which is advertised as being able to reduce evaporation by up to 50 per cent, would work. "When I saw how little product was required (200ml per 1000m² of surface area), I was sceptical," he says.
Happily, David's scepticism was unfounded. Although he did not take any proper measurements other than to mark the water level from week to week, it soon became clear that the product was working. "The rate of evaporation had reduced markedly to the point that we made it through the dry summer and autumn comfortably with water remaining in the dam."
According to David, the product was very easy to apply. "You simply pour it into the dam and it quickly spreads to form a very thin, oil-like film across the water's surface that is hardly visible," he says. It was also extremely cost effective – David estimates he spent no more than $50 on the product over the 16-week period.
David saw no indication that the silicon-based product was harmful or distasteful to stock or wildlife. "The manufacturers claim it presents no risk to grazing animals or wildlife, and certainly I didn't observe any adverse affects," he says.
With drier conditions predicted to continue, the product is giving David and Anna confidence in managing their water supplies. That hasn't always been the case, however. "We'd previously farmed in South Australia where we were used to having a bore with a windmill, or a tank and trough in every paddock," recalls David. "Having to rely entirely on surface dam water was an experience we had little knowledge of, and didn't feel very comfortable about."
The undulating property has granite-based sandy loam soils rising to rocky granite outcrops. The rocky outcrops had been fenced off, leaving two main cropping paddocks and three smaller paddocks – but just two dams to water the stock. "The stock were allowed to walk through gateways to access paddocks with water," says David. "This essentially made grazing management impossible."
With the couple intending to grow lucerne, which requires a rotational grazing system, it was clear that significant changes needed to be made to the farm layout and the watering system. They decided to build a larger dam in the best catchment, and install a reticulated watering system comprising a header tank, poly troughs and piping across the entire farm.
They also developed a whole farm plan which divided the property according to soil type – specifically, its suitability to grow lucerne. This resulted in the two larger cropping paddocks being subdivided into nine smaller paddocks, each requiring its own trough. The other paddocks also required troughs, both as a back-up for when the dams run dry, but also because the stock noticeably prefer to drink the clean water from the troughs.
Working to the farm plan, they installed a 30,000-litre header tank at the highest point of the property. An electric pressure pump was installed at the dam to deliver water to the tank (a head of around 25m). The water is then gravitated to the troughs via 40mm piping. All the lines have been set up with gate valves to isolate paddocks that are not being grazed.
In summer, the tank's capacity represents approximately 10 days' supply, but, as with any other watering system, it requires monitoring every couple of days. Occasionally the pump has required repairs or maintenance, but there has normally been adequate water in the tank to continue watering the stock during that time.
The system works well, enabling David to rotationally graze the entire farm (generally a maximum of five to seven days, followed by a rest period of between 28 to 37 days, depending on the season and paddock size). But it is only effective while there is an adequate water supply, which is why the anti-evaporative agent is now an integral part of the couple's water management strategy.
This was one landholder's experience. CSIRO has produced a paper outlining the effectiveness of various tools to reduce evaporation on dams. This publication "New tools for measuring Evaporation from Farm Dams" can be found at www.npsi.dov.au.
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