Deep testing is key to lime rates and incorporation on South Coast
Author: Melissa Williams | Date: 11 Apr 2014
Optimal liming rates and incorporation methods on the South Coast are best determined from soil testing to a depth of at least 30cm.
The extent of subsurface acidity on sandy soils in this region can’t be accurately identified by measuring pHCa in the top 0-10cm.
It is necessary to sample deeper in the 10-20cm and 20-30cm layers to pinpoint where acidity constraints occur.
The Department of Agriculture and Food WA’s (DAFWA) targets are a surface pHCa (0-10cm) of at least 5.5 and subsurface pHCa (10-40cm) of at least 4.5 (ideally 4.8 or higher).
Long term trials in WA indicate these are the levels where wheat yields will not be constrained by acidity.
Analysis of lime trial data in this State from 1991 to 2012 shows that most soils across the grainbelt are continuing to acidify and more lime is needed to reach these pHCa targets – at higher rates, on more paddocks and/or by better targeting or incorporating lime in paddocks.
Lime sources and rates
Rates of lime are best determined with an advisor/agronomist or consultant based on deep soil testing results.
DAFWA senior soil research officer Chris Gazey says growers should request standard product test results for neutralising value and particle size from their lime suppliers in order to make informed decisions and adjust rates for quality and coarseness.
He says the best lime is the cheapest per unit of neutralising value purchased, delivered and applied on-farm.
Regardless of the lime source (limesand, limestone or dolomitic limestone), finer particles will react quicker in the soil.
An audit that compares the lime sources of Lime WA Inc members, including those that supply product along the South Coast, can be found at:
Economic tools for lime comparisons
The Liebe Group amelioration calculator (found at: www.liebegroup.org.au/lime-profit-calculator) can be used to estimate the amount and cost of lime required to reach specific pHCa targets.
It was developed with GRDC funding by Farmanco, with support from the Liebe Group, and is based on DAFWA acidity models.
The calculator assesses cashflow and profits from liming versus non-liming and its underlying premise is that not liming will incur cereal yield penalties of 1 per cent per year and a 0.1 reduction in pH annually.
Another useful tool is the Lime Comparison Calculator available on the Soil Quality website (found at: www.soilquality.org.au/calculators/lime_comparison), which is supported by the GRDC Soil Biology Initiative II and Wheatbelt Natural Resource Management.
This calculator can be used to compare the cost and effectiveness of a range of lime products and the relative differences of quantities needed of various lime sources based on product specifications.
DAFWA has a worked example of using this calculator at: https://www.agric.wa.gov.au/soil-acidity/comparing-limes?page=0%2C0
Lime incorporation with cultivation
Central wheatbelt trials set up by DAFWA research officer Craig Scanlan in 2013 indicated cultivation to incorporate lime in that region 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
Craig found shifting investments away from phosphorus (P) and nitrogen (N) and into cultivation for lime incorporation on acidic soils can pay off - even in the first two years.
But the yield benefit in the first year is mainly driven by the cultivation effect.
His analysis 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 his trial sites in Dalwallinu and Dandaragan there were yield benefits of 0.4-0.6t/ha from cultivation with or without lime, versus no cultivation.
At Dandaragan, use of a rotary spader and lime did not change surface pHCa, but significantly increased pHCa at 10-20cm by 0.9 pHCa and at 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 N to deliver a 0.7t/ha wheat yield gain.
At Dalwallinu, a deep ripper followed by a one-way plough fitted with 65cm discs was used. It 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.
At this site, 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.
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.
Craig says the cultivation response at the Dalwallinu site was driven by the removal of a soil physical constraint (acidity).He says the economic success of incorporating lime with cultivation depends 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.
Craig’s 2014 Agribusiness Crop Updates paper outlining this research can be found at: http://www.giwa.org.au/2014-crop-updates.
Chris Gazey, DAFWA,
0429 107 976,
DAFWA Soil Acidity: A guide for WA farmers and consultants:
DAFWA Soil Acidity hub:
Liebe Group Lime Fact Sheet:
Liebe Group amelioration calculator:
Lime WA Inc Group – for lime product information and test results:
On-line lime comparison calculator:
See West Midlands Group member John Scotney discuss lime incorporation trials at Dandaragan in GRDC’s latest Ground Cover:
GRDC Project Code DAW00222; CSA00033; DAW00236
Region West, National, North, South