Researchers dig deeper to overcome compaction
Author: Natalie Lee | Date: 30 Nov 2015
Preliminary trial results show significant wheat yield improvements from deeper, deep ripping treatments and ameliorants applied to compacted loamy sands at Binnu in Western Australia’s northern grainbelt.
This research is part of the Grains Research and Development Corporation’s (GRDC) investment in addressing soil compaction in WA through the project ‘Minimising the effect of soil compaction on crop yield’, conducted by the Department of Agriculture and Food, Western Australia (DAFWA).
The research is being carried out by DAFWA project leader Paul Blackwell and DAFWA development officer Bindi Isbister, with valuable assistance from growers.
Soil compaction is estimated to cost WA agriculture at least $333 million annually.
As part of the compaction project, six controlled traffic farming (CTF) and deep ripping trials sites from Esperance to Binnu have been established.
CTF systems are built on permanent wheel tracks and protect grower investments in deep ripping treatments. In WA, growers generally grow crops on the wheel tracks rather than leaving them bare.
DAFWA development officer Bindi Isbister said wheat grown on loamy sands deep ripped to 55cm on the Binnu property of the Diepeveen family yielded about 2.6 tonnes per hectare, compared with about 1.9t/ha in the untreated plots.
“This response corresponds with results achieved by local growers who have tried deep ripping to 50-70cm, and recorded yield improvements of about one tonne per hectare”
Mrs Isbister said even higher yields were achieved in the Binnu trial where deep, deep ripping treatments were combined with topdressings.
“Plots ripped to 55cm and treated with topsoil down the ripping slot, or 10 tonnes per hectare of lime sand, yielded about 3.3 and 3.5 tonnes per hectare respectively, while plots treated with 10 tonnes per hectare of chicken manure produced the highest yields of about 4.2t/ha,” she said.
Mrs Isbister said that despite the significant results from the deep, deep ripped plots, areas ripped to 30cm actually produced lower yields than the unripped plots, except where chicken manure was applied.
“This might be because ripping to 30cm did not fully remove the compacted layer, meaning root access to water deep in the soil profile was limited late in the season.”
Mrs Isbister said further results from the WA trial sites would become available in coming months.
Dr Blackwell said the trials were using a ‘topsoil slotting’ technique – involving the use of a modified deep ripper with plates behind the tynes, to get ameliorants into the subsoil.
It is thought that these treatments could improve the stability of the soil.
“We think the benefits of deep ripping will be prolonged when soils are stabilised, making it more economical, sustainable and attractive to growers in the long term,” he said.
“Nitrogen-rich organic materials (chicken manure pellets), gypsum and lime are being used in the trials to evaluate whether topsoil slotting can incorporate these ameliorants to get a faster payback on deep ripping treatments, and address multiple soil constraints in one pass.
“The use of manure in the trials is to test whether we can achieve results similar to those achieved by some Victorian growers, who have recorded large, long-lasting yield improvements after incorporating chicken manure or Lucerne pellets when deep ripping.
“We will continue the trials over coming years and expect to see soil performance and the economics of investment improve over that period where topdressings have been applied.”
The soil compaction research is part of the collaborative research effort ‘Soil Constraints – West’, which was driven by the GRDC western regional panel after consultation with WA grain growers and its Regional Cropping Solutions Networks (RCSNs).
The GRDC, DAFWA, CSIRO and Murdoch University are funding the work, which is focused on non-wetting, compaction, acidity and other subsoil constraints.
More information is available in a DAFWA Deep ripping for soil compaction article available by searching ‘deep ripping’. The article includes information on how to measure compaction layers.
A GRDC Controlled Traffic Farming Fact Sheet also is available.
Information about soil management is also available on the ‘DAFWA – Soils WA’ Facebook page.
Paul Blackwell, DAFWA
08 9956 8555
Bindi Isbister, DAFWA
08 9956 8555
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code DAW00243