Eastern wheatbelt trials measure liming tactics
Bencubbin grain grower Tony Sachse is trialling aggressive tillage methods to fast-track the movement of lime into acidic and aluminium-toxic subsoils that make up parts of his 9700-hectare property.
For most of the 40 years that he has run the family operation with wife Margo – and now son Ben – he has been topdressing lime at a rate of 1 to 1.5 tonnes/ha on these areas every summer.
Surface (0 to 10-centimetres) test results for these acidic and aluminium-toxic soils show that pH is moving towards the Department of Agriculture and Food, Western Australia’s (DAFWA) minimum recommended pH of 5.5. While topsoil in some heavy clay country on the farm has a naturally occurring pH of about 7, subsoil acidity remains a major problem across tracts of the Sachse property’s variable soil types.
Some parts of the paddocks have a pH of 4 or lower, at depth, and even some of the best-producing paddocks have a pH of 4.2 to 4.3 in the 10 to 20cm, and 20 to 30cm subsoil layers.
Tony says his target for these layers is the DAFWA recommendation of a minimum pH of 4.8.
Below this level, the concentration of aluminium in soil water increases rapidly and reduces root growth. This restricts plant uptake of nutrients and water, and leads to lower plant biomass and grain yields.
“We haven’t put enough lime on in the past and, with lower-rainfall patterns in recent years, we haven’t achieved adequate incorporation of lime into the subsoil where it’s needed,” Tony says.
“It is a problem that has been gradually creeping up on us and is now a major constraint – robbing our cereal crops of up to 1t/ha in yield potential on some soil types and in seasons where rainfall cuts off in spring.”
The Sachse family has been mapping paddock zones based on soil pH testing and using a variable-rate spreader to adjust lime rates on-the-go. However, like many growers in the eastern wheatbelt and other low-rainfall areas, they are now looking to more aggressive tillage systems that can cost-effectively and more rapidly incorporate lime to depth to treat subsoil acidity and aluminium toxicity.
Often mouldboard ploughing and spading are not suitable in these areas because of erosion on lighter sands and/or cost.
In spring 2014, in conjunction with Precision SoilTech, the Sachse family used a Grizzly offset disc plough for the first time in a randomised and replicated paddock-scale trial comparing liming rates of 0t/ha, 3t/ha and 6t/ha – with and without incorporation.
Tony says he is hoping that incorporating lime to 30cm with some aggressive tillage, such as the Grizzly plough, could deliver a yield advantage of up to 0.7t/ha, if average or above-average rainfall is received in the 2015 growing season.
“If we can lift yields that much by incorporating lime with tillage, the system would pay for itself in about a year,” he says.
Precision SoilTech research officer Wes Lefroy says, to date, there has been limited research into tillage methods to incorporate lime in parts of WA’s eastern wheatbelt. This is mostly because of the big upfront cost and grower attitudes to the risks associated with issues such as wind erosion.
Mr Lefroy says there is now increasing grower interest in finding more aggressive subsoil acidity amelioration tactics to a depth of 30cm, because of the benefits in being able to fix soil pH deeper in the profile more quickly.
At the start of the Sachse farm trials, Mr Lefroy used Precision SoilTech’s guidance software and soil sampler to take samples to a depth of 50cm (at 10cm increments) at two positions in each plot and create a pH baseline map.
“With this map, we can assess individual plots for pH changes over time – rather than just yield differences across the plots,” he says.
“With a long history of soil sampling, amelioration decisions can be made with confidence because we know exactly what the soil conditions are and the potential yield of each soil type.
“In some cases, it will be more economical to bring better soils up to full potential, rather than applying lime in poorer areas.”
The GRDC’s Regional Cropping Solutions Network (RCSN) Kwinana East group has been studying economic rates and incorporation methods for lime in the eastern wheatbelt and is analysing harvest yield results from 2014 trials. □
More information:Tony Sachse,
08 9685 1257,
08 9277 5529,
0429 107 976,
Footage from the RCSN Kwinana East trials can be viewed at: http://youtu.be/egZnu55tks8 and http://youtu.be/P6D1_V1OhLQ
Watch Bencubbin grower Tony Sachse and Wes Lefroy, from Precision SoilTech, discuss lime trials using incorporation with a Grizzly offset disc plough: www.grdc.com.au/GC114V-BencubbinLiming
GRDC Project Code DAW00236