The innovative use of electromagnetic (EM) technology is enabling Moree district cropping manager Byron Birch, Rimanui Farms, to proactively manage his production risk by accurately matching crop selection with soil moisture availability.
Mr Birch uses a mobile EM38 device to take soil moisture readings across dryland black cracking clay paddocks to generate a comprehensive analysis of soil moisture availability.
The EM38 devices have been widely used for recording conductivity variance across paddocks but have recently been modelled by the CSIRO as having a close correlation to plant soil water use.
Mr Birch outlined the role EM38 devices play in farm management decisions at Rimanui Farms during the Grains Research and Development Corporation (GRDC) 2015 Grains Research Update at Goondiwindi – a showcase of important research and development projects aimed at driving improvements in production, sustainability and profitability across the Australian grains industry.
“The EM38 is quite simple; it sends a current into the soil and returns a reading. It has two ways of reading – in vertical mode it can measure down to 150cm which is perfect for wheat and it can also be turned on its side which measures down to 75cm depth which is ideal for our pulses,” Mr Birch said.
“As a management tool we are using it to determine how much fertiliser to apply pre-plant as well as to make decisions on planting opportunities and crop selection.
“This basically prevents us from planting a crop that is going to only break even or fail.”
The accuracy of the EM38s in measuring soil moisture content has been benchmarked against alternative monitoring tools by CSIRO and the Department of Agriculture and Fisheries (DAF) over the years and has been found to have an accuracy of plus or minus 1%.
The EM38 readings have a tight correlation to capacitance and neutron soil moisture curves and like probes, the EM38 requires a known range before the readings have any useful meaning. For example readings for wilting point and field capacity need to be recorded from a repeatable GPS location or certain soil type.
Undoubtedly though, the overarching benefit of using an EM38 for soil moisture monitoring is its mobility and therefore the opportunity to gain a comprehensive summary of soil moisture levels across a broad geographic spread of the paddock.
According to Mr Birch the EM38 has the ability to take accurate readings anywhere in a paddock with the identical EM classification although this requires an EM survey map of the paddock along with known full and empty readings for the relevant classified EM soil.
“In years where the profile is not at full capacity and there is doubt over sufficient stored water to grow a crop, the EM38 has the ability to measure what moisture has been stored, even in uneven cracked soils which have been filled from the bottom up,” he said.
“The EM38 has the ability to give a tangible figure which can be inputted into a spread sheet much like the probes and of course it can be used in conjunction with push probes, neutron probes and capacitance probes to verify readings.”
Probes are highly accurate tools used to measure soil water within close proximity of the probe site (1-10cm) which are ideally suited to smaller more uniform irrigation paddocks to determine how rapidly soil moisture is being utilised and irrigation scheduling.
These probes are usually installed post emergence in an area of uniform plant establishment and are able to settle into the surrounding soil after the first irrigation.
Mr Birch believes the use of capacitance and neutron probes in dryland farming poses a number of limitations, primarily due to their relative permanency.
“Dryland farmers want to know how much soil moisture they have prior to planting in order to make decisions on whether or not to plant and therefore the probe needs to be installed during the fallow,” Mr Birch said.
“Probes work best when they have settled into the surrounding soil. This increases the risk from damage to spray rigs, planting rigs and headers.
“Also operators have a tendency to drive around or lift over probes with planting rigs, which results in probe readings being inconsistent to the rest of the paddock.”
The expense of capacitance probes often prohibits larger broadacre growers from placing a unit in every paddock, yet for low rainfall years knowing the moisture status of each paddock is extremely important for management decision-making.
While neutron probes are significantly cheaper, they still require installing and time specific management during busy operational periods such as sowing and harvest according to Mr Birch.
He said farmers needed to know how much moisture was left at the end of each season to accurately measure water use efficiency.
“Paddock soil moisture is often estimated at the end of a crop cycle due to the properties of dry soil, that is, soil being air dried around probes as localised cracking forms or the inability to penetrate push probes through the dry top soil.
“Probe placement is subject to a multitude of unforeseen variables such as localised runoff areas flowing to probe sites or vice versa, running away.”
That said, Mr Birch believes that push probes, neutron probes and capacitance probes can be effectively used in conjunction with the EM38 to verify readings. He said it was critical for growers to calibrate correctly for soil moisture readings and to follow the operational instruction manual when using an EM38 otherwise accuracy would be compromised.
To hear Mr Birch discussing his experience with using the EM38 to measure available soil moisture, download his interview with Driving Agronomy.
Driving Agronomy is one of several free-to-air audio programs produced on behalf of GRDC and is available as a podcast. For instructions on how to subscribe via iTunes or platforms other than iTunes, or to download previous programs, visit the Driving Agronomy webpage.
Caption: The use of an EM38 device is enabling Moree district cropping manager Byron Birch, Rimanui Farms, to determine how much fertiliser to apply pre-plant as well as to make decisions on planting opportunities and crop selection.
Byron Birch, Cropping Manager, Rimanui Farms Ltd
Sarah Jeffrey, Senior Consultant, Cox Inall Communications
08 9864 2034, 0427 189 827