- Soil testing during summer to at least 30cm (in 10cm increments) will identify acidity.
- Liming can be more effective using paddock ‘zones’ and better positioning product in the subsurface.
- Liming in zones should initially focus on maintaining pH in soils that meet recommended levels and then targeting the most productive areas that are below recommended pH.
- It may be economical to cut back on phosphorus and divert investments to lime.
Targeted lime application is a key tool to overcoming soil acidity and boosting rain-limited crop yields across the bulk of Western Australia’s wheatbelt.
There can be positive spin-offs on subsurface acidity and compaction if lime is mechanically incorporated down the soil profile when growers are using spading, deep ripping or mouldboard ploughing.
Subsurface acidity and compaction have been identified as major research priorities by the Grains Research and Development Corporation’s (GRDC) Regional Cropping Solutions Networks (RCSN) across WA.
Geraldton port zone RCSN facilitator Cameron Weeks said his group would like to see the majority of growers in their region applying the required rates of lime to fix subsurface pH (which should be measured calcium chloride solution - pHCa).
Cameron Weeks, left, of Planfarm Geraldton, coordinates the GRDC’s Geraldton port zone RCSN and is with GRDC regional program manager - west Darren Hughes. GRDC has identified subsurface acidity and compaction as major R,D&E priorities. PHOTO: Cox Inall Communications.
He said the traditional practice of top-dressing lime at one to two tonnes per hectare was no longer enough to lift long term yields if lime levels had not been historically maintained.
“To get quicker returns on investment and crop productivity gains, efficiencies are needed in positioning lime down the soil profile and targeting paddock ‘zones’ using variable rate technology,” he said.
“Zoning is important because you will get more bang for your buck by concentrating lime on the areas where it is needed most.
“Maintenance liming should be scheduled for paddocks with good pH and then the most productive areas targeted where pH needs to be recovered to recommended levels.”
Mr Weeks said many cropping paddocks in WA’s northern wheatbelt now had good phosphorus (P) levels, so P investments could also start to be diverted to lime.
He estimated growers could save about $15 per hectare per year by not applying standard P rates on paddocks that had sufficient levels.
This could contribute to the estimated cost of $50-$65/ha (or $5 to $6.50/ha/year over a 10-year period) to apply quality lime at the commonly recommended rate of 2.5 t/ha across the WA wheatbelt.
It is estimated 14.25 million hectares of WA’s wheatbelt soils are already acidic or at risk of becoming acidic.
This erodes potential crop yields by about 9 to 12 per cent, worth almost $500 million annually.
Department of Agriculture and Food, Western Australia (DAFWA) senior soil research officer, Chris Gazey, said for WA’s agricultural soils the minimum pH levels to maintain or achieve yield potential were:
- Surface pHCa of 5.5 in the 0-10cm layer
- Subsurface pHCa of 4.8 in the 10-20cm and 20-30cm layers
- No less than pHCa 4.5 in the 10-30cm layers to avoid aluminium (Al) toxicity.
He said when these targets were met, wheat yields would not be constrained by acidity.
“But the time taken to achieve this will vary according to factors such as: starting pH profile; amount, frequency and quality of lime applied; sensitivity of the rotation; and degree of reliance on subsurface moisture at the end of the season,” he said.
“Typically, amelioration and potential lime responses can take five or more years after application.”
The table below highlights the amount of lime commonly needed in the central wheatbelt to reach DAFWA’s soil pH targets.
| Soil depth
||Lime amount over 5 years
| < 5
| 2 t/ha
|| < 5.5
|| < 4.8
|| < 4.8
||measure pH in 3 years
Rule-of-thumb lime guide developed for the Avon Catchment Council in WA. Source: DAFWA
Progress towards targets
The quality, quantity and application method of lime required is predominantly determined by soil type and pH profile, which should be tested in 10cm increments to at least 30cm every three to four years. Summer is the ideal testing time.
To assist with lime calculations, pure calcium carbonate (100% neutralising value) applied at 1 t/ha will increase topsoil (0-10cm) pH by about 0.7 on sand, 0.5 on loam and 0.3 on clay in one to two years.
Higher quantities of agricultural lime are needed to achieve these results and Mr Gazey said the best product was the cheapest per unit of neutralising value delivered and spread on farm.
“Fine particle size is important when liming to recover acidic soil because it will react quicker to neutralising the acid,” he says.
Crop effects on acidity and the lime schedule
WA wheatbelt soils have steadily become more acidic since they were first developed for agriculture.
Mr Gazey estimated that average alkalinity (lime) removal was about 150 to 200 kg/ha annually – or the equivalent of about 1.5 to 2 t/ha of lime per decade.
He said product removal and leaching of nitrate through inefficient fertiliser use were the main contributors.
“About 9kg of lime is removed per tonne of wheat and up to 60 kg/t is removed if you harvest lupins and bale the stubble,” he said.
“At a conservative estimate of 50% nitrogen efficiency, lime requirements are about 5.8kg per 1kg of N.”
More targeted lime application
Long term WA trial data shows top-dressed lime can take five or more years to significantly increase subsurface pH below 10cm. Few trials have shown an immediate response to top-dressed lime.
“This is because it takes several years for surface-spread lime to work its way down to where it really matters in the root zone,” Mr Gazey said.
“If surface pHCa is maintained at or above 5.5, there is downward movement of alkalinity and if subsurface pHCa is above 4.8, this will prevent Al toxicity.”
An alternative is to mechanically incorporate lime down the profile. This will dissolve the lime more rapidly when it contacts the acid soil and fast-track this process.
A GRDC-funded and DAFWA-assisted Liebe Group trial at Michael O’Callaghan’s Marchagee farm in 2012 found average wheat yields increased by 0.1 to 0.8 t/ha when lime was placed deep in the soil profile (at a rate of 3 t/ha), compared to control plots with lime but no deep incorporation. Minimum tillage was used and cultivation could have contributed to these responses.
On poor sand areas at this trial site, yields were doubled from the control plots (average 0.3 t/ha yield) using lime and deep ripping (0.6 t/ha); were 133% higher for lime and spaded plots (0.7 t/ha); and 267% higher for lime and mouldboard ploughed plots (1.1 t/ha).
On better sand areas in this trial, yields were 77% higher than the control (average 1.3 t/ha yield) in lime and deep ripped plots (2.3 t/ha); 85% higher for lime and spaded plots (2.4 t/ha); and 108% more for lime and mouldboard ploughed plots (2.7 t/ha).
At the West Midlands Group 2013 trials in WA’s central wheatbelt, soil profiles were scraped clean and sprayed with a pH indicator dye to show the subsurface effects of lime incorporation methods. Low pH is shown as orange and higher pH as green/purple. PHOTO: Joel Andrew, Precision SoilTech.
Liebe Group project officer Nadine Hollamby said these improvements were driven by higher plant biomass, improved tillering and higher wheat head densities where a combination of amelioration and lime was used.
She said this indicated better plant uptake of nutrients and higher water use efficiency.
The West Midlands Group undertook a series of side-by-side trials in 2013 at Peter Negus’ Dandaragan farm in the central wheatbelt comparing six mechanical lime incorporation methods at lime rates of 3 to 5 t/ha.
The aim was to assess the effectiveness of lime amelioration techniques and whether any methods could be profitable in the first year.
Barley yields and economic returns from these trials are currently being analysed. But early soil testing results indicated only deep tillage methods – deep ripping, rotary spading and mouldboard ploughing – were able to incorporate lime into the acidic 20-30cm subsurface layer.
WMG trial coordinator Dave Gartner said these techniques also removed some soil compaction and mild water repellence issues at the site.
“Some of the shallower lime incorporation methods used in the trial – offset discs, scarifying and one-way ploughing - appear to have incorporated some lime into the 10-20cm layer, but not in the 20-30cm layer,” he said.
DAFWA deep ripping and rotary spading trials at the same Dandaragan site in 2013 found cultivation and lime increased soil pH in the 10-20cm layer in year one by 0.3-0.9 units, compared to liming with nil cultivation.
Economics of liming
Where enough lime has been applied to remove the acidity constraint, all long-term DAFWA trials in WA have shown the practice has been economical and profitable.
The key is to apply sufficient lime to achieve soil pH profile targets.
The cost of transporting and spreading lime is a significant proportion of the total cost of liming, so it is important that growers calculate the total on-farm cost based on neutralising value and particle size.
Lime WA Incorporated provides lime product information and test results to enable comparison of lime types and quality.
A lime calculator can help to determine the appropriate quantity and costs of lime application (including freight and incorporation methods) to address specific soil pH conditions.
The Liebe Group released a soil amelioration calculator last year, developed with GRDC funding, that can determine cashflow and profits from liming versus non-liming.
It is based on the assumption that not liming in the wheatbelt will incur cereal crop yield penalties of 1% per year and an annual reduction of 0.1 in soil pH.
Chris Gazey, DAFWA,
0429 107 976,
Cameron Weeks, RCSN Geraldton port zone,
0427 006 944,
Nadine Hollamby, Liebe Group,
08 9661 0570,
Anne Wilkins, WMG,
08 9651 4008;
DAFWA Soil Acidity: A guide for WA farmers and consultants:
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:
GRDC Project Code
SP11-01226: LIE00006; DAW00014; DAW00146; DAW00204; DAW00222; CSP139; UWA 00081; UWA00259
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