Knowledge streams from soil moisture probes

Key points

  • Probes help make better farming decisions
  • Data primarily used to make in-crop nitrogen decisions 

Despite the dry finish to the 2014 growing season, data from soil moisture probes installed on South Australian growers Ashley and Tom Robinson’s property (owned, leased and share-farmed land) gave them confidence they would finish with reasonable yields.

Photo of Tom Robinson

Tom Robinson says data from soil moisture probes has helped determine target yields on his family’s property at Halbury, South Australia.

PHOTO: Alistair Lawson

The Robinsons crop 1600 hectares at ‘Anashka Farms’, Halbury, in SA’s mid-north, and grow predominantly LongReach Cobra wheat with some LongReach Trojan and Hyola® 559TT canola.

They installed two soil moisture probes in early 2012 – one on their home block and another at an outlying block five kilometres to the west – after operating under a zero-till system for the previous 14 years.

“We wanted to monitor soil water to start making better farming decisions,” Tom says. “The main reason for the probes was to make in-crop nitrogen decisions based on how much plant-available water we have.

“However, we also wanted to look at our varieties to make sure we were growing crops that rooted deep enough into the soil and to make sure we were getting the best water use efficiency.

“By looking at the graphs generated by the probes, we can see how deep the plants are rooting. In the future, as more research is done into varieties, I can see we will be choosing not only for yield but for water use efficiency as well.”

The probes

The probe on the home block features a weather station, which gives a snapshot of rain, wind speed, temperature, soil temperature, daily sunlight and relative humidity every 30 minutes. Both probes go down to 90 centimetres.

The Robinsons also host a South Australian No-Till Farmers Association trial site (Tom is president of SANTFA), which has its own soil moisture probe.

The probes were installed by AgByte’s Leighton Wilksch, who manages the devices for the Robinsons. Tom and Ashley are able to access the data generated by the probes on a smartphone, tablet or computer.

They access the data generated by the probes twice a week and, throughout the growing season, make all fertiliser decisions on the resulting information.

The Robinsons use the French–Schultz model combined with a theory championed by SA consultant Jeff Braun – 60 kilograms of grain yield per millimetre of plant-available water at flowering time for wheat – to formulate their target yield.

“The data from the probes gives us a yield to aim for,” Tom says. “We look at how much plant-available water there is in the bucket and make final decisions based on that. We know we can grow a certain amount of wheat for every millimetre of plant-available water and we know what we need to fertilise for that amount of yield.”

In-crop decisions

Before sowing this year, the Robinsons knew, thanks to the probes, they had an abundance of soil moisture and had the confidence not to skimp on seeding or fertiliser rates.

Ashley says from GS21 all crop management decisions were based on data provided by the soil moisture probes.

“We don’t really use the data from the probes to influence our time of sowing as we are typically calendar sowers,” he says. “But from the probe data we knew early in the season that we had a fair yield potential.

“If we’ve got a good soil moisture profile – which the probes can tell us – then we are comfortable to go out early with nitrogen and get a good early canopy on the crops, knowing we are able to sustain that.

“An early canopy is important as the head size is determined at GS31 and if the plant has good nutrition then we might be able to trick it into forming a better head structure. A good early canopy and early growth is important, provided we don’t go too hard with it.”

However, a good start ended in a bad spring with minimal rain and a dry finish. At the end of July, soil moisture probe data showed a full profile of soil moisture down to 90cm and 153cm of plant-available water.

Through spring, there was very little rain at the Robinsons’ property. However, they knew they still had enough stored moisture in the profile to get them through to the finish.

And despite some frost damage and a small incidence of beet western yellows virus, yields were still coming off pretty well when harvest started at ‘Anashka Farms’ in early November.

“We knew we had a frost-affected crop this year before we went out and inspected it because one of the probes was reading –2.2°C one metre above the soil surface,” Ashley says. “That, and the fact that we had 14 mornings below zero in the space of 28 days through August.”

The probes gave Tom and Ashley an insight into how much water the crops were using.

“During August the crops were using 6mm a day,” Ashley says.

Summer options

In September, the Robinsons sowed a 40ha patch of sunflowers, knowing they had 100mm of plant-available water in the profile. Despite only receiving minimal rain during spring, the sunflowers emerged well and were developing at a good rate heading into summer.

Tom says they are looking to diversify their rotation by sowing summer crops such as sunflowers.

“The question has always been ‘Can we grow a summer crop?’,” he says. “The way I’m looking at it now is that we might be able to grow a winter cover crop for more ground cover and, to introduce some diversity into the system, spray that crop out and sow sunflowers into it. That decision will be made based on whether or not there is enough plant-available water.

“Sunflowers are very good at extracting water that wheat and canola can’t. So we are drying out the profile and by having a winter cover crop we’re creating more cover, more plant diversity and getting a legume into our system.

“By doing that we will hopefully be able to grow a summer crop that is beneficial to our end goal – good soil health.”


Leighton Wilksch

Photo of Leighton Wilksch

PHOTO: Deanna Lush

As farms get bigger with fewer people on the ground to do the work and make management decisions, AgByte director and agronomist Leighton Wilksch predicts predicts that the popularity of soil moisture probes will increase.

Mr Wilksch, who specialises in the installation and management of soil moisture probes, says the probes have extremely accurate sensors every 10 centimetres, which tell the grower where the moisture is in the soil profile and from where the plant roots are actively drawing moisture. However, this information only comes from an area of about 10cm radius around the probe.

“As a result, it’s important to ensure the probe is installed in a representative soil type for the paddock or farm,” Mr Wilksch says.

“The real power of the data, particularly in August and September, is that you can see where plant roots are extracting moisture and how much moisture is left to help the crop reach its yield potential.

“The other major benefit is the year-on-year analysis of the data. Once a grower has had a probe in for three years, the software can display a graph to compare years and crop water use.”

Mr Wilksch says the three management areas in which probes help decision-making are when and what to plant, nitrogen and other nutrient decisions, and during spring when it is possible to estimate yield based on the amount of plant-available water in the profile.

“I’ve had clients make decisions such as putting more or less canola in or planting wheat early based on the data they have from the probes,” he says.

In 2014, AgByte installed about 30 probes, a number which Mr Wilksch says has been increasing over the years. He says many growers – both in mixed-farming systems and continuous cropping systems – are opting to install soil moisture probes with weather stations, giving them information such as rainfall, temperature, humidity, wind speed and wind direction.

“Farms are being managed more centrally from a home base of maybe 20 to 30 kilometres or more away,” he says. “The moisture probes allow management decisions to be made from the office or wherever you have your smartphone or iPad.

“This year-on-year logging of information becomes pretty useful. You can look back in 10 years’ time and see what happened last time you had a wet winter and dry finish, what management decisions you made at the time and how that might be applicable to the current day.”



Craig Davis

Photo of agronomist Craig Davis

Tom and Ashley Robinson’s agronomist, Craig Davis, is always picking their brains to find out the latest data from their soil moisture probes.

“I’m always asking about the data as an aid to quantify crop yield potential and to get a more accurate understanding of what kind of moisture is available to finish the crop off,” Mr Davis says.

“We also use the data to fine-tune fertiliser decisions, specifically with nitrogen. The majority of the data is used to clarify yield potential based on finishing conditions and stored moisture.”

Mr Davis says the data from the probes can also be used post-harvest to see if there is any residual carryover moisture.

“If there has been some carryover, that may change our decision as to how much nitrogen we put down the following year or we might adjust our planting decisions based on the moisture available,” he says.

“It also helps to justify other inputs, such as whether or not to spend $5/ha on a fungicide or $15/ha. A lot of that is based on yield potential, so it justifies the decision we make there.”

Mr Davis expects soil moisture probes to become more common, much like yield monitors on headers.

“It’s another way to get useful data to help in the decision-making process,” he says. “Almost everyone has a smartphone these days that could in future be set up to easily receive the information from the probes.”

A video on Using soil moisture probes to make better farming decisions is available at: 

More information:

Tom Robinson,
0400 291 219,;

Leighton Wilksch,;

Craig Davis,
0447 541 654,


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