On-farm trials probe hostile subsoils

On-farm trials probe hostile subsoils in Victoria


Southern
Rokewood, Victoria, grower Andrew Whitlock in Southern Farming Systems lupin soil acidity trials on his property. PHOTO: Brad Collis

Rokewood, Victoria, grower Andrew Whitlock in Southern Farming Systems lupin soil acidity trials on his property. PHOTO: Brad Collis

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On-farm trials investigate effects of incorporating lime with discs and deep-ripping.

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Victorian grower Andrew Whitlock aims to tame the dark, subterranean depths of the soil profile where hostile acidic subsoils are thought to be limiting yields on his cropping country at Rokewood, about 130 kilometres west of Melbourne.

Consequently, Andrew is closely observing new subsoil amelioration trials, established in April on the 2000-hectare property he runs with his wife, Sophie, and her parents, Tim and Julie Bingley.

These on-farm trials, run by Southern Farming Systems in partnership with the New South Wales Department of Primary Industries, are looking at the effects of incorporating lime with discs and deep-ripping, as well as deep-ripping with applied lime or lucerne pellets.

Prompting his interest in the trial findings is Andrews expertise as founder and technical director of the consultancy Precision Agriculture, specialising in precision soil pH mapping to guide variable-rate lime applications, which are mostly spread on the soil surface.

Having already spread lime on the surface of his own paddocks to treat acidic topsoils, Andrew is now looking deeper in the soil profile below 20 centimetres to the problem of acidic subsoils.

Hinting at the scope of this problem and the yield limitation posed, he says his own experimental trial in 2017 oats showed deep placement of prilled or pelletised lime with the seed increased the crops yield by 15 per cent.

As such, he hopes the GRDC-invested study from 2015 to 2020 will help identify the most cost-effective amelioration options for treating acidic subsoils on his familys property, as well as those of his Precision Agriculture clients across south-eastern Australia.

Strategic soil sampling showed our deeper, lighter soils prone to subsoil acidity were linked to low EM conductivity zones. - Andrew Whitlock

Showing his drive to implement new management approaches identified through the research, Andrew has been using complementary precision agriculture technologies to provide a clearer picture of the acidic soils that require treatment deep in the duplex soil profile.

For example, he uses normalised difference vegetation index (NDVI) mapping for acid-sensitive crops to determine where acidic soils or other constraints might be limiting crop growth, as well as electromagnetic induction (EM) mapping to gauge clay distribution in the subsoil.

Andrew explains that low pH tends to occur in his light-textured subsoils, so acidity is less likely in heavy-textured subsoils containing clay and, in turn, this information can be used to guide deep lime applications.

Strategic soil sampling showed our deeper, lighter soils prone to subsoil acidity were linked to low EM conductivity zones, he says.

Using this novel approach to subsoil pH mapping, Andrew now plans to ameliorate the soil at depth on about 20 per cent of his 400ha cropping area, targeting soil pH of 5 (calcium chloride).

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