Target lime to quicken pay-off
GroundCover™ Issue: 108 | Author: Melissa Williams
There can also be positive spin-offs if lime is mechanically incorporated into the subsurface while growers are spading, deep-ripping or mouldboard ploughing, to alleviate soil compaction or address other soil constraints.
Subsurface acidity and compaction have been identified as research priorities by the GRDC’s Geraldton Port Zone Regional Cropping Solutions Network (RCSN).
RCSN facilitator Cameron Weeks says the traditional practice of top-dressing lime at one to two tonnes per hectare is no longer enough to lift long-term crop yields if lime levels have 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 by targeting paddock ‘zones’ through variable rate technology,” he says.
“You will get more ‘bang for your buck’ by concentrating lime on the areas where it is needed most.”
Mr Weeks suggests growers schedule in ‘maintenance liming’ for paddocks with good pH, and then target the most productive areas where pH needs to be recovered to recommended levels.
“Many cropping paddocks in the northern wheatbelt now have good phosphorus (P) levels, so P investments can also start to be diverted into lime.”
It is estimated growers can save about $15/ha by not applying standard P rates on paddocks with sufficient levels.
This could contribute to the estimated cost of $50 to $65/ha (or $5 to $6.50/ha/year over a 10-year period) to apply quality lime at the commonly recommended rate of 2.5t/ha across the wheatbelt.
About 14.25 million hectares of WA wheatbelt soils are already acidic or at risk of becoming acidic. This erodes potential crop yields by about 9 to 12 per cent – a cost of almost $500 million a year to the WA industry.
Department of Agriculture and Food, Western Australia (DAFWA) senior soil research officer, Chris Gazey, says for WA’s agricultural soils, the minimum pH – measured in calcium chloride (pHCa) – to maintain or achieve yield potential is:
- surface pHCa of 5.5 in the 0 to 10 centimetre layer;
- subsurface pHCa of 4.8 in the 10 to 20cm and 20 to 30cm layers; and
- no less than pHCa 4.5 in the 10 to 30cm layers to avoid aluminium (Al) toxicity.
He says when these levels are met, wheat yields will not be constrained by acidity.
“But the time taken and amount of lime needed 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 says.
Long-term WA trial data shows top-dressed lime can take more than five years to significantly increase subsoil pH below 10cm.
An alternative is to incorporate lime down the profile. This will dissolve it 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 0.8t/ha when lime was placed deep in the soil profile (at a rate of 3t/ha) compared to control plots where there was no cultivation.
Liebe Group project officer Nadine Hollamby says these improvements were driven by higher plant biomass, improved tillering and higher wheat-head densities where amelioration and lime were used – indicating better plant uptake of nutrients and higher water use efficiency.
The West Midlands Group undertook side-by-side trials in 2013 at Peter Negus’s Dandaragan farm to compare the effectiveness and profitability of six mechanical lime-incorporation methods.
Barley yield results from the trial are currently being analysed, but early soil testing indicated only deep tillage methods – deep ripping, rotary spading and mouldboard ploughing – were able to incorporate lime into the acidic 20 to 30cm layer.
These techniques also removed some soil compaction and mild water repellence issues at the site.
Economics of liming
A lime calculator can help determine the appropriate quantity and costs of lime (including incorporation methods) needed to address specific soil pH conditions.
The Liebe Group released a soil amelioration calculator last year, developed with GRDC funding, that can assess cashflow and profits from liming versus non-liming.
It is based on the assumption that not liming will incur cereal yield penalties of one per cent per year and a 0.1 reduction in pH annually.
More information: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;
Useful resources:DAFWA – Soil Acidity: A guide for WA farmers and consultants: www.agric.wa.gov.au/#publications-4
Liebe Group Lime Fact Sheet: www.liebegroup.org.au/factsheets (click on ‘Deep incorporation of lime’)
Lime WA Incorporated Group – for lime product information and test results: www.limewa.com.au
Online lime comparison calculator: soilquality.org.au
Liebe Group lime profit calculator: www.liebegroup.org.au/lime-profit-calculator
GRDC Project Code LIE00006, DAW00204, CSA00016, CSP139, UW00081, UWA00259, DAW00014, UWA00131, DAW00146, DAW00236