AgResearch senior scientist Dr Val Snow and Auckland University acoustics physicist Professor Stuart Bradley and have been leading work into better understanding the link between sound, water and run-off. They told Richard Rennie about their work.
A joint research project between AgResearch and Auckland University scientists at the leading edge of technology is using sound waves to determine optimal irrigation levels.
Known as the Surface Water Assessment and Mitigation for Irrigation (SWAMI), the technology is being used to define a relationship between how sound waves bounce off the soil surface and controlling irrigation applications.
AgResearch senior scientist Dr Val Snow says the traditional means of determining optimal irrigation levels for modern precision irrigation systems usually relies on measuring soil moisture levels and using that to adjust application rates.
“But what existing precision systems can’t take account of is the effect of free water that ponds on the soil surface. This is water that can go one of three ways.
“It may run off, taking nutrients, sediment and bacteria with it, it can seep through a macro-pore in the soil and be lost to the plant, possibly ending up in the water table or thirdly it may simply sit there and over time damage the soil’s health, making that soil more vulnerable to the effects of pugging and consolidation.”
The ponding can be caused by systems simply not being able to deliver at a low enough rate to match the soil’s absorption, particularly on heavier clay soils or where the soil is already too wet in places.
With electricity costs constantly creeping up, regional councils seeking greater proof of placement for irrigation and tightening constraints on nutrient losses researchers believe their work will be well received by farmers as it moves to larger-scale trials next summer.
The most basic components of the system are an array of speakers that direct a sound signal at the soil surface with the signal’s return picked up by an array of microphones.
“This is really the low-cost part of the technology with the real smarts sitting behind the arrays,”Auckland University acoustics physicist Professor Stuart Bradley says.
As the signal bounces off the soil surface the presence of ponded water will cause the sound signal’s volume to shift.
The patented technology developed in the joint venture is still in its early stages but researchers are starting to find an algorithmic relationship between the signal change and the amount of ponded water on the soil.
Typically, the more ponded water on the surface the closer the bounced sound signal mirrors the original signal.
“We are finding the shift in the sound signal occurs in the range of about 0-30% of the soil surface being ponded, which is a really realistic, workable range – if it had worked over, say, only 0-5% it really would not have been as useful,” Snow said.
The next step for researchers is to figure out what the trigger is to vary irrigation water application.
“Ultimately, we can see a series of these units on a centre pivot arm, providing immediate feedback to control the flow of applied water.”
In areas where water ponding is detected as being too high by the technology a signal will turn water flow off.
Bradley and Snow are confident the technology can be economically fitted to variable-rate irrigation systems, with even small savings in water use seeing it pay back in a short period.
“This is subject to further study, hopefully from our next funding round, but the more information we get back the most positive this is looking. Early what-if modelling indicates you don’t need to reduce water use by much to easily recoup the cost of the equipment on a variable-rate system,” Snow said.
So far trials have been done on a relatively small irrigation system with a larger-scale, commercial trial scheduled for the coming season.
Snow said funding has come through the Ministry for Business, Innovation and Employment’s Smart Ideas programme.
Bradley said the work has linked his past work on rainfall to his more recent work in acoustics while the joint venture process has proved invaluable in sharing expertise.
“It has been very much a case of the sum being greater than the parts of the project.”
