GroundCover™ Issue: 135 July - August
Goomalling grower Rob Dempster is confident the production potential from yellow sandplain soils on his family’s property can be “unlocked” to become an asset – especially in dry seasons.
He says the main challenge is finding the most cost-effective amelioration option to overcome the multiple constraints of water repellence, compaction and subsoil acidity.
Rob, his brother Dan and father Vern participated in research into the impacts of a range of soil-inversion and deep-tillage tactics on crop performance conducted by consultancy group agVivo Pty Ltd, with GRDC investment and support from the Department of Primary Industries and Regional Development (DPIRD).
Trials on their farm in 2017 included deep-ripping, very deep-ripping (with a Gregoire Besson Heliripper), modified one-way ploughing, mouldboard ploughing, spading, delving, rotary hoeing and combinations of these techniques.
An exceptionally dry start to that season highlighted the particular issue of water repellence on the yellow sandplain soil, which the Dempsters targeted with clay incorporation in the late 1990s.
In the past six years, Rob says, the family has also tried using a rotary hoe, mouldboard plough and deep-ripper, and found all have had benefits and drawbacks.
“The deep-ripping we attempted on 300 hectares before seeding in 2015 solved the hardpan compaction problem, but exacerbated the water-repellence constraint,” he says.
“Perhaps this was because we deep-ripped when the soil was dry.
“After that, we undertook extensive soil testing to depth and realised we have a fairly bad subsoil acidity problem on the farm that we needed to address alongside the water-repellence constraint.”
Rob says the dry start in 2017 also led to poor canola germination in paddocks treated with a mouldboard plough, mostly as a result of higher clay content causing crusting at the soil surface.
He says the agVivo Pty Ltd trial results and the family’s experience to date indicate the most efficient and cost-effective way to address this is likely to be a one-way modified disc plough used with deep-ripping.
“This leaves some organic matter close to the soil surface and reduces the risk of clay sealing,” he says. “It may not be the single silver bullet that solves every constraint, but it could be the most suitable strategy for optimising our farm business profitability.”
Rob has used a modified plough concept designed by the Plozza brothers of South Eneabba on an old Chamberlain plough bought by his father in the 1970s. He says it can work faster than a mouldboard plough or spader to address water repellence and compaction and allows incorporation of lime to depth to address acidity.
agVivo Pty Ltd consultant Tim Boyes, who managed the trials on the Dempsters’ farm, says the research was not just about finding the ultimate solution to the three main soil constraints, but also making the economics work.
“We wanted to ensure a profitable outcome for Rob, Vern and Dan’s business in the long term,” he says. “To do this, we analysed a range of treatments, effectiveness in attacking the main soil constraints and the gross margins of each option.”
In 2017, Mr Boyes says, there were positive crop yield responses on most of the trial plots, particularly the very deep-ripping and delving treatments (either standalone or in conjunction with spading), mouldboard ploughing and one-way ploughing.
He says preliminary findings indicate there is much value in using a one-way modified plough system, but only when accompanied by deep-ripping at this site.
“It’s easy to modify some of the older one-way ploughs, cheap and practical to use these and they require less experience to set up and operate than a mouldboard plough,” he says.
“Also, there can be negative outcomes from mouldboard ploughing when you are inverting the entire soil profile.
“This was apparent in last year’s dry start to the season, where large amounts of clay were brought to the soil surface – affecting soil crusting post-seeding and seedbed establishment.”
Tim says other local growers will benefit from this GRDC project, as the soil type used for the Dempsters’ trial is highly representative of that found across large tracts of the central grainbelt.
GRDC Research Codes DAW00244, AVP00003-A
0447 915 643
Tim Boyes, agVivo Pty Ltd
0458 181 478