Knowledge streams from soil moisture probes
GroundCover™ Issue: 114 | Author: Alistair Lawson
- 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.
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 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.”
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.
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.”
More information:Tom Robinson,
0400 291 219,
0447 541 654,