Soil type, texture and plant-available moisture are everything to Moree Plains mixed farmer Broughton Boydell.

A noted pioneer of precision agriculture research, the fifth-generation grower has spent decades exploring soil’s relationship to crop yield outcomes using numerous tools, including electromagnetic (EM) mapping, to understand soil conductivity at a range of depths.

“My interest in yield monitors was really helping me to understand soil type and how to take that understanding to better manage and optimise for higher yields; not uniform yields, but optimised yields,” he says.

Broughton farms 2700 hectares with his wife Natalie at ‘Marinya’ and ‘Romaka’, near Pallamallawa, east of Moree. They grow wheat, barley, chickpeas and canola as dryland winter crops and cotton as a dryland summer crop. They also run about 150 Angus cows producing Angus calves.

Broughton’s father, Craig, embraced conservation tillage in the 1980s, followed by a shift to no-till as part of what Broughton calls “the glyphosate revolution”. By 1998 they had converted to controlled-traffic farming (CTF) on tramlines.

“That process was all around keeping as much stubble on the surface as possible,” he says.

The aim is to protect or secure the soil and to manage heavy rain to prevent erosion and promote infiltration through a better soil structure. Most farm equipment operates on 12-metre and 36m widths. Grain crops are planted on 333-millimetre row spacings and cotton on 2.4m rows.

By reducing compaction, CTF gives the soil more space between particles, which translates into higher water-holding capacity and less damaging run-off from intense storms.

Broughton says average annual rainfall may be 625mm, but it is highly variable from year to year and even within years. Rainfall records have been shattered over the past five years, with a record annual low of 189mm in 2019, followed two years later in 2021 by a record high of 1086mm.

Wheat is the pillar crop and has traditionally been followed by inter-row sown barley to maximise ground cover, then – seasons permitting – cotton and a double crop of chickpeas. The alternative is cotton, then wheat, chickpeas and barley.

But that is about to change, as Broughton aims for a lower risk, less intensive rotation that allows the soil profile to store more moisture during a long fallow period.

“I think going forward, we’ll probably be more likely to be wheat then chickpeas, then wheat and cotton, then fallow around to wheat,” he says.

Preferred varieties include Sunmax and LRPB Raider wheat, RGT Planet barley, CBA Captain chickpeas and, occasionally, Pioneer® 45Y93 CL canola.

Other changes in the works include planting cotton a month later, in November, to reduce plant stress during peak summer heat after Broughton noticed the varieties Sicot 606B3F and Sicot 619B3XF were pulling up shorter than older varieties.

EM maps harnessed for smarter inputs

Broughton pursued his interest in soils and soil health off-farm, studying soil science at the University of Sydney (USYD) before completing a master’s in precision agriculture at the University of Georgia (UGA) in the US.

Broughton

Boydell and his wife Natalie grow dryland winter grain crops and cotton

in summer near Pallamallawa, east of Moree. Photo: Melanie Jenson

UGA

considers Broughton’s dissertation on yield mapping of peanuts as one

of two studies that pioneered its precision agriculture research in the

mid-1990s.

Back on home turf, he began managing the family farm and undertook a PhD in precision agriculture at USYD, studying in-field variability and developing a yield monitor for cotton.

Broughton used sensors to explore the relationship between stored soil moisture and crop yield outcomes. To get a good understanding, he used Veris sensors and other EM devices, including a DUALEM capable of measuring both electrical conductivity and magnetic susceptibility to at least two defined depths.

As an example, a paddock at one of the farms, ‘Romaka’, contains areas of black soil. This soil is capable of holding 200mm or more of plant-available water (PAW) at full profile. This compares with red sandier soil, which has half the PAW capacity.

“Eight years in 10, we might expect two tonnes or 3t to the hectare on the red soil and 3t to 4t or better on the black soil,” Broughton says.

The family farms were not prone to salinity so, instead of mapping zones based on electrical conductivity, Broughton created zones according to the soil’s full-profile water-holding capacity.

“Water-holding capacity is what we use to make input decisions, and the main one is nitrogen fertiliser,” he says.

“We have varied seeding rates; we’ve done all sorts of things, but the main one that we’re managing or trying to optimise is nitrogen.”

Broughton says he and his father Craig settled on a Hood-Robin approach, where they would “rob nitrogen from the poor (low water-holding capacity) soil and give to the rich”.

They do not apply the same volumes of fertiliser on both black and red soils to try to produce similar yields, even at variable rates used since 1998. Instead, they essentially allocate more nitrogen to the black soils and less to the red.

Broughton had calculated that applying 100 units of nitrogen on black soil would likely result in a 5t/ha, 12.5 per cent protein wheat crop 12 years in 20, compared with one year in 20 on the red soil.

“Optimising fertiliser appropriately for the yield potential, I’m going to fertilise for a 3t crop on the red soil and a 4.5t crop on the black soil,” he says.

a) A satellite image of the bare paddock, West Creek, shows differences in soil type at ‘Romaka’. b) A yield map in GreenStar™ Apex™ 3.4 highlights the difference in sorghum yields harvested from different soil types across a paddock. c) Soil conductivity measurements taken in the top 90cm using a Veris sensor across a paddock. Source: Broughton Boydell

Innovation beyond the paddock

Since 1997, Broughton has combined his practical experience in farming with technical roles at John Deere, where he is now a senior staff engineer in the Advanced Engineering Group.

In 2001 – along with Andrew Smart, Guy Boland and Colin Lye – he co-founded Precision Cropping Technologies (PCT), a startup using EM surveys and soil testing to better interpret the drivers behind yield map variability.

Broughton uses software from T3RRA – a company PCT started in 2012 – to update contour banks that eliminate localised waterlogging and optimise water flow, slowing it down so it does not carry sediment, but still safely directs water off paddocks.

He has not lost the research mindset that sparked his initial studies, putting in strip trials across the farms every season to compare crop responses to fertiliser types, rates and depths.

“We’re just trying to learn how to optimise these different approaches on our farm. The faster you can learn that you’ve done the wrong thing, the quicker you can respond,” he says.

“We’re constantly learning from little observations ... if you think about actual soil type and soil texture and water-holding capacity, that really helps you understand, a lot of the time, why things that you’re observing are happening.”

Targeted weed management

Working for John Deere has its perks, including early access to prototypes for testing such as the John Deere R4045 self-propelled sprayer equipped with See & Spray™ Select technology.

Broughton says using the rig for the past six years has also highlighted the link between soil type and weeds, with coarser textured red soil the most expensive for weed management, as well as being the lowest-yielding areas.

“Now that we know the weeds are heavily influenced by soil type and microtopography, we’re particularly interested in solutions,” he says.

“We might look at applying a residual herbicide on red soil that we might not put on the black soil.”

The spectrum of weeds has changed in the past 20 years, from milk thistle and fleabane until five years ago, to feathertop Rhodes grass, fleabane, barnyard grass and herbicide-tolerant wild oats.

Broughton is cautiously employing strategic tillage to help manage weed blowouts.

“Predominantly, weeds that blow are our main ones, and we do not have them under control,” he says.

“We thought we did, and then we didn’t. It was quick. With my background in soil science, I’m really nervous about cultivating wet soil, dry soil or cultivating at all.”

This article appeared in GroundCover