GROWERS applying clay to overcome subsoil constraints on Western Australia’s south coastal sandplain soils will achieve maximum yield benefits if the clay comprises 5-7 per cent of soil.
This is one finding from a five-year project in the region investigating sandplain soil management and claying, funded by the Grains Research and Development Corporation (GRDC) and conducted by the Department of Agriculture and Food (DAFWA).
DAFWA senior researcher David Hall said experiments near Esperance had revealed that the correct amount of clay incorporated in to the soil could improve canola, lupin and barley yields by 30 to 100 per cent, depending on soil types.
“But clay applied too heavily and poorly incorporated produced either no effect, or reduced yields – clay applied at high rates can turn the soil in to a ‘clay brick’ in which crop root systems fail,” he said.
“In these situations, spading machines have been used to improve clay incorporation and turn around a paddock from being a disaster to an asset.”
Mr Hall said growers should analyse the clay content of their soils, as well as the actual clay content of material being applied, and not apply clay at blanket rates across all paddocks.
“Many growers in the region have been applying clay at a particular tonnage across their farms, regardless of the type of clay being applied,” he said.
“It would be better for growers to take a softly, softly approach, and apply clay on a paddock by paddock basis, and assess the results.”
Mr Hall said non-wetting soils were the most significant soil constraint facing South Coast growers, and claying offered an immediate, long-term solution to the problem in this region.
Deep-ripping to address soil compaction in the GRDC funded trials had provided additional yield increases of up to 20 per cent, with improved yields continuing for three years after the treatment.
Mr Hall said the project revealed that claying treatments were most profitable when non-wetting soils were the only significant subsoil constraint.
“If there are many subsoil constraints, the payback period may be extended,” he said.
“Also, some non-wetting soils may already be achieving 80 per cent of potential crop yields – in these cases growers need to consider whether the cost of applying clay is justified.”
Mr Hall said growers could also consider cheaper soil amelioration options such as furrow sowing and surfactants.
Growers can obtain more information about sandplain soil management and claying through the DAFWA bulletin Managing South Coast Sandplain Soils to Yield Potential, available by contacting Mr Hall at david.hall@agric.wa.gov.au
The project investigating sandplain soil management and claying was conducted as part of a national GRDC subsoil constraints initiative.