How paddock science solved a soils puzzle
GroundCover™ Issue: 119 | Author: Melissa Marino
In this instalment of the Ground Cover matchmaker series highlighting advances made through grower–researcher collaboration, we look at how zero-till systems have been used to combat water repellence in sandy soils
The researcher – Margaret Roper
It was the mid-2000s when some curious information came to Dr Margaret Roper’s attention. Growers with sandy soils on Western Australia’s south-east coast were reporting that water repellence problems had disappeared in their zero and no-till farming systems.
This appeared to contradict scientific evidence that higher organic matter in the soil can cause water repellence because plants produce waxes that inhibit water infiltration. Therefore the more plant material, the more wax particles and the greater the water repellence – particularly in sandy soils, which are prone to wax coating due to their small surface area.
“Generally speaking, if you’ve got a sandy soil with a lot of organic matter in it, it will be quite highly repellent,” says Dr Roper, who by then had been researching microbial degradation of waxes to improve water infiltration for a decade. “The fact that they were seeing water repellency disappear was totally counter-intuitive to the information we had on water repellency at the time.”
However, Dr Roper, a CSIRO microbiologist who has a history of working collaboratively with growers, was compelled to investigate the claims, including those of Munglinup grower Doc Fetherstonhaugh, that their crops were no longer exhibiting the symptoms of water repellence.
For Dr Roper it was shaping up as a classic example of the potential for in-the-field reality to contradict a laboratory-based hypothesis. “Laboratory experiments have their place … but you can’t always project a farming system in a laboratory experiment,” she says. “And the visual evidence in the district was that despite the water-repellent soils, no-till crops were emerging evenly and flourishing.”
Dr Roper says that with this and other research, listening to growers is critical. “They are very good observers and often observe things that are contrary to general thinking. And if you are open-minded enough to listen and explore, sometimes you can come up with very valuable information. And that’s what happened at Doc’s.”
Doc Fetherstonhaugh’s property at Munglinup was an ideal testing ground. Under zero-till for 15 years, a large tract had recently been burnt in a fire caused by lightning. This meant trials could be undertaken with varying burnt and unburnt treatments on land subject to identical environmental conditions and soil type.
Large-scale trials, funded by the GRDC, were established in 2008 with four distinct treatments: zero-till unburnt; zero-till burnt; cultivated unburnt; and cultivated burnt.
Treatments were managed by Doc and his brother Barn, and the research, led by
Dr Roper with colleagues Phil Ward, Ramona Jongepier and Shayne Micin, included measuring water repellence, infiltration, soil carbon and crop performance.
To date, the team has unearthed some startling results. It found that the initial theory still stood. Areas under zero-till were more severely water-repellent due to higher levels of organic matter. The zero-till unburnt soil was the most repellent and the burnt-cultivated system was the least repellent.
However, despite its higher water repellency, the zero-till system actually retained more water. “You would expect that the burnt-cultivated soil would have taken up much more water because it was less repellent, but when we measured water in the field the zero-till unburnt treatment had more water in the soil – and the least water was in the cultivated-burnt,” Dr Roper says. “So it’s completely the opposite of what you would expect.”
The “significant” differences in water retention had also been expressed in the crop, she says. Plants under zero-till had much better emergence – more than double that of other treatments. “And we found this year after year,” she says.
These results were achieved, she says, because despite greater water repellence on the surface, root canals preserved in the zero-till system allowed water to travel beyond the sandy, water-repellent top layer to the root zone, where the soil profile changed and water repellence was not such an issue.
This was proven in pre-sowing trials using blue dye to reveal the movement of water, which, on the burnt and cultivated plots, pooled on the top of the soil unable to penetrate. “It had been cultivated the day before – the soil was really soft and fluffy – but there were no pathways and the dye just sat on the soil and dried and crusted,” Dr Roper says.
In contrast, the dye in the zero-till system followed old root channels from the previous season’s crop into the wettable layer of soil containing less organic and waxy material, where it spread. “The difference in the two trials was striking,” she says.
After sowing, further tests showed root pathways from the previous year’s zero-till crop continued to conduct water into the soil. Longer term, continuous measurements of soil water on the four sites showed that cultivation was the biggest hindrance to water infiltration in the inter-row, Dr Roper says. “Essentially, the take-home message is the crop inter-row under cultivation will not conduct water.”
Dr Roper says the research undertaken at the Fetherstonhaugh property demonstrates that a zero-till disc system will combat the negative effect of water-repellent soil. “The conclusion we would draw is don’t cultivate and don’t burn – don’t move stubble at all,” she says. “The key is keeping those root pathways intact. If you can do that you can get water into the system.”
This is a useful insight for growers dealing with water-repellent soils, which are relatively commonplace with up to 10 million hectares of cropping land at risk in Western Australia, South Australia and western Victoria.
Dr Roper’s research with Doc Fetherstonhaugh shows it is possible to achieve good results without having to clay the soil or dramatically change its profile, which, while shown to be successful, can also be expensive.
Encouragingly, she says, for those wanting to move to a zero-till system, long-term trials at Doc’s show water infiltration improves quite rapidly – within about 12 months – once cultivation stops and root pathways re-establish. Recovery from burning, though, appears slower.
Dr Roper says such insights for working with water-repellent soils would not have been gained were it not for Doc providing the researchers with a real environment in which to test. This is why working hand-in-hand with growers is so important, she says. “Unless you can get out there and demonstrate things on-farm you can’t say they work or are valuable at all.”
Despite pencilling-in a retirement date in 2016, Dr Roper is still very much involved in co-research with growers. She is still analysing trials on the Fetherstonhaugh property and has a new project underway with Pingrup grower Paul Hicks looking at water infiltration and crop performance when sown on-row versus sowing on the inter-row.
Utilising iTILL® technology developed by Paul that allows for seeding on the old row with minimal soil disturbance, the GRDC-funded project, although in its infancy, is showing greater numbers of wax-degrading bacteria in the on-row soil where there is more moisture.
Although there is not yet a proven direct link, Dr Roper says more wax-degrading bacteria could be reducing water repellence and improving crop performance. And because more wax-degrading bacteria proliferate where the soil is wetter for longer, this is further evidence that a system that promotes water infiltration is ideal to combat non-wetting soils – such as the zero-till disc system.
“It relates back to what Doc is doing because maintaining root pathways maintains water in soils, which allows these microorganisms to grow,” she says. “If your soil is dry, nothing will happen.”
While only planning to stay in Western Australia for two years when she arrived in 1992, Dr Roper is still there, with the topic of water repellence running through much of her work aimed at improving productivity. “It’s always been fascinating because it’s so multi-faceted,” she says. “There’s an agronomy component, a microbial component and a mechanical component and it has allowed me to go out into the field and kick over the soil.”
The grower – Doc Fetherstonhaugh
It may not have seemed very fortuitous at the time, but the lightning strike that hit the Fetherstonhaugh farm in December 2004 turned out to be quite a stroke of luck.
The subsequent hot-burning fire, while melting wire and wiping out retained crop residues, also created the ideal conditions for a field trial that would help set the parameters for growers trying to combat water-repellent soils.
With just 40 of 1000ha spared, the scene was set to compare burnt paddocks with those that had remained untouched; and unburnt and not cultivated for 15 years under a zero-till system. But without the fire, Doc Fetherstonhaugh doubts there would have been any trials of that nature at his property at all.
“We wouldn’t have deliberately burnt, and certainly not such a large area,” he says. “Because of the size of the fire it took us some time to get back into top productivity but at least we could see, from the results of the trials, exactly how to do that.”
Essentially, the fire created a living laboratory where tests could be carried out side-by-side on paddocks with four distinct parameters. With zero-till and cultivated systems able to be trialled on both burnt and unburnt stubbles, researchers could gain insights into how the Fetherstonhaugh soils were retaining water despite being water repellent.
“They designed experiments to test what we were saying all along – that non-wetting was no longer a major issue for us,” he says. “And that didn’t seem to make sense to the scientists.”
Doc already had an idea that the zero-till practice he introduced after moving to the area was playing a role, but the question was how. “Our soil looked better, was behaving better and we could sow our crop when we wanted and it would all come up without an issue,” he says. “People were trying to work out what was going on. They were saying ‘it can’t work like that’ and it seemed to defy everyone’s expectations.”
By collaborating with the researchers, Doc and other growers in the sandy-soiled region got their answers. And that was that despite organic matter technically, and in isolation, increasing water repellence in soils, in a zero-till system those effects were being offset by other factors.
“Just a tiny bit under the topsoil it was damp and because the mulch protects the soil from the sun and wind and because you retain the roots and root channels, we were letting moisture in a lot easier and the moisture wasn’t running off,” he says. “So even though the soil was technically in the lab behaving as non-wetting, in the field it was behaving exactly the opposite.”
The findings, he says, gave him great confidence in the zero-till system that had already brought so much improvement to his family’s land. “We knew then that what we had been seeing was real,” he says. “And we were on the right track.”
Today, the property looks very different than it did in the summer of 1986 when Doc and his wife Bernadette, along with his brother and sister-in-law Barn and Cate, moved to Munglinup from South Australia.
The family bought a farming system that revolved around 10,000 head of sheep. The soils were sandy, gravelly and light and the land almost completely cleared of trees, Doc says.
“The combination of sheep and the coastal winds meant that every year there would be huge areas of the district blowing away in sand and dust storms,” he says. “It was pretty bloody average to be honest. It wasn’t good.”
To counteract the effect of the devastating coastal fronts, the family began planting trees on the highly erodible, highly water-repellent land that had been under cultivation for years. Then, prompted by plummeting wool prices, in 1992 the family destocked.
“We could see that with a lot of rain – it’s a 520-millimetre rainfall area – there was potential to grow good crops if we could get our act together.” The Fetherstonhaughs went to a no-till system first, with a pressed wheel/knife point system – one of the first of its kind in the state – and pre-dating the deep blade seeder (DBS) system commonly used today.
With total retention from the outset, stubbles quickly built up, but it was too much for the knife-point system so they switched to a disc seeder. Since then, the system has not changed too much, Doc says, with the dual-rotation wheat/canola system improving each year and returning annually between 1.6 and 1.8 tonnes/ha of canola on average and 3t/ha of wheat.
Doc says water repellence was still an issue in the first few seasons of no or zero till, but over time the problem seemed to disappear with crops emerging uniformly year after year. So while it was no real surprise when the researchers confirmed his observations, it was a revelation that his soils were still as repellent as ever and it was his system that was mitigating the effect.
This insight, confirmed in the trials comparing cultivated, burnt and zero-till sites, has helped his management of the farm into the future, he says. For example, it has ensured he will not be tempted to either cultivate or burn as a quick-fix to a problem such as weeds.
Weeds are controlled through removing weed seed at harvest, a herbicide regime and natural attrition, he says. A switch to GM canola about five years ago has also helped, particularly in removing ryegrass.
Doc, who was a longstanding member of the GRDC Regional Cropping Solution Network for the Esperance Zone and has National Variety Trials at his property, says he enjoys hosting scientists conducting “real research” into agriculture. This is because robust science can help improve systems across the board and strengthen grower insights, he says.
“You really need good, solid, quantifiable evidence to say ‘you are going in the right direction’, or that ‘the direction is wrong’,” he says. “Whatever it is, we need to know and there’s still so much research that could be done.”
Dr Margaret Roper,
08 9333 6668,
0427 751 006,
GRDC Project Code Doc Fetherstonhaugh projects: CSP00098 (2008-09); CSP00117 (2009-10); CSP00139 (2010–15); DAW00244 (2014–19) led overall by DAFWA’s Stephen Davies with Phil Ward leading the CSIRO component Paul Hicks projects: CSP00139 (2010–15) and continuing in DAW00244
Region South, West