Precision liming tackles severe acidity
Western Australian grain growers Brady and Erin Green have been reaping the benefits of a range of technologies adopted to address subsurface compaction and acidity on their ‘Carrawingee Farms’ property near Yuna.
An overhaul of their farming system has led to efficiency gains in key target areas – improving soils, optimising crop water use efficiency and maximising soil nutrient extraction.
After droughts in 2006 and 2007, the Greens implemented disc seeding and controlled-traffic farming (CTF) as they sought to retain crop residue and reduce soil subsurface compaction and acidity.
They adopted the no-till system pioneered by specialist systems agronomist and farmer Robert Ruwoldt in Victoria’s Wimmera and are making it work on the acid sand plains of the northern wheat belt.
A $20,000 Federal Government ‘Caring for our Country’ trial coordinated by the local Yuna Farm Improvement Group (YFIG) was set up on their property in 2010 to compare the effects of CTF, mouldboard ploughing and deep ripping on grain yields, and subsurface compaction and acidity.
Brady says good yield results from the deeper soil amelioration techniques in this trial triggered a rapid evolution of their cropping system.
“We started to use biomass imagery to diagnose consistently poor yielding areas of the farm and identify areas that were highly acidic and/or had aluminium (Al) toxicity,” he says.
“Soil moisture probes were also installed for better crop monitoring.”
In 2012, the Greens undertook an ambitious project to map soil pH across their whole property by sampling (to a depth of 50 centimetres) at 160 sites using the YFIG deep soil sampler.
Samples were processed in a do-it-yourself lab installed in their workshop.
Brady says this soil pH data was combined with biomass images and Google Earth and yield maps to create production ‘zones’ with the initial aim of applying variable rate technology (VRT) to inputs, including lime.
He says this led to a whole-farm approach to precision agriculture, purchase of a deep ripper and a switch back to tyne seeding.
“We recognise our next big efficiency gains will come from correcting subsurface acidity and getting lime to depth,” he says.
“We have been top-dressing lime at a rate of 1 to 1.5 tonnes per hectare for the past 15 years, but this has not kept pace with requirements.
“Our soil testing showed the worst areas of the farm had a pHCa of 4.4 at depth, highlighting that pH was a big issue for the bulk of the property.
“Our aim is to lift average surface pHCa to 5.5 and subsurface pHCa to 4.8.
With the help of GRDC-funded Department of Agriculture and Food, Western Australia (DAFWA) pH research, the Greens developed a soil pH index. They used colour-coded index results to create zones according to the severity of acidity.
“These zones surprisingly do not correlate to soil types or crop yields, but indicate where the farm’s most severe problem areas are,” Brady says.
He says the initial aim was to use VRT for liming across the farm, but index results highlighted that more lime was needed right across general areas.
“Variation within paddocks was not enough for VRT just yet,” he says.
“But in the longer term, when we have recovered pH levels, we will use VRT to finetune lime applications for areas where pH is still low.”
Brady says he is gearing up to buy and handle a lot more lime in the future. The closest lime source is 70 kilometres away and costs about $65/ha to deliver and spread.
The Greens’ average liming rate is 2t/ha on sandplain areas and application is now more targeted, with incorporation to a depth of 20cm using deep-ripping tynes that create a ‘V’ channel.
After six years, results from this farming systems approach have been positive.
“We are noticing more consistency in our crops,” Brady says.
“The CTF system, combined with inter-row sowing at 381 millimetres has given us the ability to establish crops evenly and lift yields.
“The greatest benefits are not the yields of today, but the improvements coming tomorrow as we witness a continuing improvement in our soil quality – which is our biggest asset.”
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