Secrets of soil movement unearthed
GroundCover™ Issue: 111 | Author: Rebecca Jennings
University of South Australia researchers are investigating ways to improve seeding success and efficiency in no-till farming systemsAdelaide’s suburban sprawl may encroach, and the hum of a major north–south arterial route is in the air, but the University of South Australia’s (UniSA) Mawson Lakes campus is a farming heaven.
Here, the Agricultural Machinery Research Group’s workshops house seeding, tillage and harvesting machinery, cutting-edge agricultural technologies and even a self-propelled autosteer lightweight vehicle, which could be used for automated soil sampling.
A walk around the precinct also reveals its 250-metre-long tillage test track, where a continuous sandy loam ‘soil bin’ between the rails allows tillage tools to be tested under repeatable conditions.
It signals the group’s long-term work to advance no-till seeding technologies for improved seed placement accuracy and maximised crop establishment, vigour and yield.
In recent years, researchers have taken a closer look at the fundamentals of soil/tool interactions to shed light on the soil force system acting on disc seeder blades and how soil movement is induced by no-till furrow openers.
Although some lateral soil throw is often desirable for adequate pre-emergence herbicide incorporation, too much stimulates weed seed germination, dilutes furrow moisture and buries surface residue, leading to increased risk of soil erosion.
Over the past four years, as part of his PhD studies, Dr Aliakbar Solhjou from the Fars Research Center for Agriculture and Natural Resources in Iran has helped fill some research gaps, thanks to co-funding by the GRDC and UniSA.
Dr Solhjou homed in on narrow-point openers, which are used to open soil and place seed and fertiliser into the furrow. These openers can create excessive soil throw, even when used at typical sowing speeds, and result in crop damage.
As well as exploring how the geometry of a narrow-point opener can influence soil movement, he tested an innovative concept based on a bent-leg opener and studied how the conformation of a bent-leg opener may affect soil movement.
Using UniSA’s indoor seed-placement test rig, Dr Solhjou attached tillage tools to a frame that moves over bins of soil at desired depth and speed. He was able to trace how far and in which direction each soil layer moved by inserting a grid pattern of small PVC cubes acting as tracers.
When the furrow opener moved through the bin, these tracers were thrown with the soil and later located using a 3-D digitising frame to quantify soil movement, layer by layer.
The project highlighted how much a furrow opener’s geometry affects soil movement. The shape, angle, width and face of openers contribute to the distances and directions that soil from each layer moves.
For example, vertical narrow openers with a two-sided face (chamfer) can increase furrow width, reduce forward and lateral soil movement and reduce the depth of soil layers being thrown out of the furrow, compared with a blunt-face vertical opener.
When it comes to the effect of rake angle, a furrow opener with a low rake angle (for example, 35 degrees) is much more effective at clearing dry topsoil away from the seed zone and bringing moist deep soil into the seed zone – important when sowing into a drying soil proﬁle.
Conversely, a larger rake angle better maintains furrow backﬁll and may minimise soil moisture loss out of the furrow. Under experimental conditions, a rake angle in the range of 50 to 55 degrees achieved the widest band of cleared surface soil, which may contribute to higher crop safety if pre-emergence herbicides are incorporated by sowing.
Under the experimental soil bin conditions (eight-kilometre-per-hour speed and 120-millimetre depth) at no-till row spacings upto 250mm, all opener rake angles moved significant topsoil onto the adjacent furrows, with potential crop-safety implications when using pre-emergence herbicide.
The research also focused on the benefits of bent-leg openers, which have never been studied in the context of no-till seeding. Combining specific bent leg features with a leading face chamfer allowed soil throw to be cancelled or controlled to appropriate levels, while loosening large size furrows suitable for seed and fertiliser placement.
Associate Professor John Fielke, associate head of teaching and learning at UniSA’s School of Engineering, says the sowing system technology research has identified opportunities for more effective seeder implement design and usage.
“The findings have implications for optimising no-till seeding practices, for example, when seeding into marginal moisture, as well as improving crop safety and in-furrow weed control when pre-emergence herbicides are incorporated by sowing.”
It does not just shed light on seeding solutions for Australian growers. UniSA agricultural research engineer Dr Jack Desbiolles is involved in no-till projects in North Africa and the Middle East.
“Although zero-till disc-seeding technology has been adopted to a small extent on bigger farms in north Africa, tyned seeders are a simpler and lower-cost option for the majority of growers with smaller farms, who are not adopting no-till practices due to affordability issues,” Dr Desbiolles says. “We are focusing on direct-seeding strategies associated with low tractor power and simplified low-soil-disturbance tyne seeding systems, for which the option of low-soil-throw openers are just as important.”
He says understanding how furrow openers work in the soil also contributes to the development of improved management solutions for root diseases such as Rhizoctonia solani; for example, moving the top soil layer (where the highest concentration of disease inoculum lies) out of the seed zone to reduce the disease pressure on developing seedlings.
Looking ahead, Associate Professor Fielke says the sowing-system technology research paves the way for other PhD students, who will extend the bent-leg research into field context by assessing expected benefits of reduced weed germination and technology development for seed and fertiliser banding.
More information:Associate Professor
John Fielke, 08 8302 3119,
GRDC Project Code USA00005
Region Overseas, South