Cultivation to incorporate lime can be more economic than topdressing where:
• Soil pHCa in the 0-10cm layer is well below the recommended 5.5
• Soil pHCa in the 10-20cm layer is well below the recommended 4.8
• The cultivation implement mixes at the depth of the pH constraint
Researchers are starting to devise economic and productivity parameters around cultivating to incorporate lime on acidic soils, rather than topdressing lime.
This stems from 20 years of soil acidity research in WA, which has found yield benefits from liming are highly variable and depend on the severity and depth of soil acidity and the extent to which liming had ameliorated this constraint.
What is clear from long term research outcomes, which were presented to the recent Agribusiness Crop Updates by Department of Agriculture and Food WA (DAFWA) senior soil research officer Chris Gazey, is that - across most of the grainbelt - lime application rates need to be more than 2 tonnes/ha to recover poor soil pH profiles.
Recent trials coordinated by DAFWA research officer Craig Scanlan show that cultivation for lime incorporation on acidic soils can pay off - although the yield benefit in the first year is mainly driven by the cultivation effect.
Craig set up GRDC-funded trials at Dandaragan and Dalwallinu in 2013 to quantify the effects of cultivation and incorporating 3t/ha of limesand on soil nutrient availability.
These trials showed that net margin (income from grain minus all fertiliser, tillage and lime costs) was about the same for no or very high rates of fertiliser when incorporating lime.
At both sites there were yield benefits of 0.4-0.6t/ha from cultivation, which offset the costs of the cultivation and some lime application.
Rotary spader and lime trials – Dandaragan 2013
Rotary spading with and without lime incorporation to a depth of 35cm was assessed at Craig’s Dandaragan trial site.
Cultivation using the rotary spader (without lime) significantly reduced soil pHCa in the 0-10cm layer, but increased pHCa in the 10-20cm layer, compared to the control plots with no cultivation or lime.
Cultivation with lime incorporation did not change surface pHCa, but significantly increased pHCa at 10-20cm by 0.9 pHCa and 20-30cm by 0.8pHCa - compared to nil cultivation and no lime.
Total soil nitrate in the 0-40cm layer increased by 32kg/ha to 80kg/ha by cultivating with lime using the rotary spader, compared to nil cultivation and no lime.
Craig estimates this is enough soil nitrogen to deliver a 0.7t/ha wheat yield gain.
Average wheat yields (the trial was sown with Magenta wheat) in the trial ranged from:
• 2.5t/ha for the control plots with no cultivation or lime
• 3.1t/ha for cultivation and lime
• 3.1t/ha for cultivation with no lime.
Craig says the cultivation benefit at this site was predominantly driven by an increase in the mineralisation rate of organic matter.
He says incorporation of lime with cultivation did not lift yields beyond the cultivation effect most likely because soil pH was already above target levels.
Deep ripping with lime – Dalwallinu 2013 trials
At Dalwallinu, a deep ripper followed by a one-way plough fitted with 65cm discs was used. This was set up for cultivation depths of 30cm for the deep ripper and 20cm for the one-way plough and trialled with and without lime.
Cultivation (without lime) significantly reduced surface pHCa (0-10cm layer) by bringing acidic subsoil to the surface. But when lime was added, soil pHCa in the 10-20cm layer increased.
Soil nitrate levels did not change with cultivation at this site, most likely due to a small organic pool of N being available for mineralisation.
Average yields (from Mace wheat) at this site were:
* 1.7t/ha in the control with no cultivation and no lime
* 2.1t/ha for cultivation and lime
* 2.1t/ha for cultivation and no lime.
Craig says it is most likely that incorporating lime with cultivation did not lift yields above those achieved with cultivation alone in this first year of the trial because only a small proportion of soil was ameliorated by the one-way plough. But he says the yield benefit achieved by cultivation was enough to offset the cost of cultivation and some lime application.
Craig says there is likely to be future benefit from lime incorporation with cultivation because acidic subsoils will be ameliorated at least two or three years faster than if lime was topdressed.
Incorporating lime increased the availability of soil phosphorus.
Applying no P fertiliser at the Dalwallinu site caused an average yield loss of 0.6t/ha in the control plots with no cultivation or lime.
This was double the yield loss in the cultivated plots where P was omitted at 0.3t/ha and significantly more than the 0.1t/ha lost in the cultivation plots with lime and no P.
Yield losses from omitting N were not significantly different between treatments - at 0.2-0.3t/ha.
Craig says the cultivation response at the Dalwallinu site was driven by the removal of a soil physical constraint.
He says the economic success of incorporating lime with cultivation depended on the implement being able to mix to the depth where the soil constraint occurred. If this is not achievable, the benefits of incorporating lime should be weighed up against the costs of cultivation, risks to crop emergence and potential soil erosion risks.
Other lime incorporation methods
The West Midlands Group (WMG) assessed a range of tillage methods for incorporating lime into acidic subsoils in 2013. Growers in this region are finding it can take three to five years for topdressed lime to significantly increase pHCa in the 10-20cm and 20-30cm layers.
With GRDC funding, the WMG trialled lime incorporation with a scarifier, offset discs, a one-way plough, a deep ripper, a rotary spader and a mouldboard plough (and a combination of deep ripping followed by spading) on Baudin barley.
They found deep ripping removed compaction at the site to a depth of 40cm and rotary spading and mouldboard ploughing removed compaction to a depth of 30cm, potentially allowing lime incorporation to those depths.
One-way ploughing, scarifying and offset discs could loosen the soil and incorporate lime to the 10-20cm layer. There was no significant impact of lime or tillage on crop establishment or final grain yield.
This could have been due to a good season finish, more powdery mildew on bulkier deep cultivated plots and/or highly variable soil pHCa at the site.
The WMG says the trial highlights the importance of measuring subsoil pHCa levels and applying sufficient rates of lime to prevent and correct subsoil acidification.
Where tillage is used to incorporate lime, it is important to know the depth that this will achieve and which subsoil layers need correction.
This trial will be monitored for the next two years and the WMG will also start a Council of Grain Grower Organisations (COGGO)-funded project in 2014 to further assess deep ripping modifications and flexible systems that allow amelioration and liming with stubble retention.
This involves modifying the deep ripping process to increase the flow of loose limed topsoil immediately behind the tyne into the acidic subsurface.
Larger slots behind the deep ripping tynes will hold the slot open for longer and deliberately direct the flow of loose limed topsoil into the slot. The aim is to reduce the risks of wind erosion by enabling some stubble cover to be retained after the lime incorporation.
Long term trial – Mingenew – enough lime is never enough
Analysis of data from 69 WA lime trials set up between 1991 and 2012 by Chris Gazey and CSIRO’s Yvette Oliver found there is an average potential long-term yield gain of 0.18t/ha – or 10 per cent – from liming.
This increased to 12 per cent if the first two years of data were removed (on the understanding lime takes time to react in the soil). Yields were higher where ripping/tillage was used.
A stand out case study in this data set was a long-term response to liming trial established in 1994 near Mingenew. This highlighted that rates of lime previously considered adequate do not ameliorate soil pH to depth.
Initial treatments were 0, 0.5, 1, 2 and 4t/ha of lime, followed by 1t/ha of lime applied in the years 1998, 1999, 2003 and 2012 as part of normal paddock operations.
This liming regime increased or maintained surface pHCa (0-10cm) above 5.5-6 for all initial treatments. But only the plots that initially received 4t/ha – with another 4t/ha applied by the grower in subsequent years – had subsurface pHCa levels that were close to the recommended level of 4.8.
These plots yielded 10 per cent higher in 2013 than the plots with no lime initially.
Plots that received less than 2t/ha initially continued to acidify below 20cm depth and by 2013, were yielding up to 6 per cent less.
Photo caption: At the West Midlands Group 2013 trials, soil profiles were scraped clean and sprayed with a pH indicator dye to show the subsurface effects of a range of lime incorporation methods. Low pH is shown as orange and higher pH as green/purple. (Credit: Joel Andrew, Precision SoilTech.)
Craig Scanlan, DAFWA,
08 9690 2174,
Chris Gazey, DAFWA,
0429 107 976,
Anne Wilkins, WMG,
08 9651 4008;
2014 Agribusiness Crop Updates Papers: http://www.giwa.org.au/2014-crop-updates
DAFWA Soil Acidity: A guide for WA farmers and consultants: www.agric.wa.gov.au/#publications-4
DAFWA soil acidity information hub: https://www.agric.wa.gov.au/climate-land-water/soils/soil-constraints/soil-acidity
Liebe Group Lime Fact Sheet: http://www.liebegroup.org.au/wp-content/uploads/2012/01/factsheet-subsoil-acidity-final-12022013.pdf
Liebe Group amelioration calculator: www.liebegroup.org.au/lime-profit-calculator
Lime WA Inc Group – for lime product information and test results: www.limewa.com.au
On-line lime comparison calculator: soilquality.org.au
See John Scotney discuss West Midlands Group lime incorporation trials in the latest Ground Cover: Ground Cover 109: www.grdc.com.au/GC109
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