Moisture probes offer BIGG scope



The use of soil moisture monitoring technology is becoming more common in cropping operations and almost standard in viticulture but remains an unexplored frontier in grazing systems.

A group of Barossa Valley graziers and mixed farmers believe the technology could bring major benefits to their pasture management systems.

The Barossa Improved Grazing Group has installed three demonstration weather stations – featuring soil moisture probes, rainfall gauges and temperature and humidity sensors – in pasture paddocks at Flaxman Valley, Keyneton and Koonunga.

While the benefits of monitoring soil moisture in grazing systems are largely unknown or untested, farmers at a BIGG soil moisture monitoring workshop at Keyneton said the technology had the potential to become an important tool influencing their decision making.

The workshop helped explain how the technology works, how farmers can access data from the trial and how this might eventually in their farm management.

The weather stations have been installed in traditional grazing pastures at Flaxman Valley and Keyneton while the Koonunga site is cropped after a period of pasture as part of a rotation system.

Graham Keynes’ Keyneton site has been rotationally grazed for 10 to 15 years, and contains a mixture of sub clovers and annual grasses.

“It’s important to give the pastures a rest regularly, so we’ve been splitting paddocks into smaller areas to give us more control,” he said.

“It’s probably time for more perennials to be put back in – we’ll probably look at sowing some coxfoot and phalaris.”

Each of the sites have 80-centimetre long probes, measuring soil moisture at 10cm intervals from a depth of 15cm below the surface. The probe is attached to the weather station via a buried cable.

The solar-powered weather station transmits soil moisture, temperature, humidity and rainfall data every 15 minutes using the mobile phone network. This data is then available live online, with farmers able to see the latest figures and long-term trends on their computers, tablets or smartphones through the BIGG website.

BIGG technical facilitator Brett Nietschke said the data would be of no benefit unless farmers knew what it meant and how to apply it on-farm.

“We’ve got all this data, but it won’t mean anything unless we know how to use it in our every day decision making,” he said.

Rural Directions director Tony Craddock has been working with the technology in dryland cropping for five years and says the key to its usefulness comes in identifying plant-available water levels.

“We’re interested in the water that’s available to the plants, not the total water in the soil,” Mr Craddock said.

He said plant-available water was calculated by first determining the drained upper limit and the wilting point.

“When water reaches its saturation point, some will always drain through the soil and what you’re left with is the DUL,” he said.

“The wilting point is the point where all the remaining water is too tightly held to the soil for the plants to access it. Plants will start to go off at this point, even though your moisture monitor would still be telling you there’s moisture there.

“Plant-available water is the difference between the DUL and WP. Once we know the plant-available water levels – which can take a couple of seasons to work out – we can know how full the soil water bucket is.

“We can then work out how quickly moisture is being used, how many days of soil moisture we’ve got left and even how far into the profile rainfall is penetrating.”

He said applications for the technology would come to light as the trial continued.

“Five years ago, broadacre farmers didn’t know all the applications,” he said.

“I’m sure it will be the same in grazing – you’ll be amazed by how useful it will be.”

More benefits identified by speakers at the workshop included the ability to determine how many weeks of pasture growth remained if no further rain fell, with farmers able to base stocking rates around this data. It could also help to work out if different pasture species could make better use of available water.