OVERCOMING subsoil constraints in SA’s sandy soils has been shown to boost crop yields by up to 180 per cent, according to PIRSA’s New Horizons project.
Now the focus of an expanded five-year, GRDC-funded project is to find the most cost-effective treatments for farmers to apply to their paddocks.
PIRSA Rural Solutions SA consultant Melissa Fraser says results from Eyre Peninsula, Mallee and South East sites show overcoming high bulk density, low water-holding capacity and poor fertility in sandy soils can substantially lift production.
“Previously all our soil work has been in the top 10 centimetres but we know improving the root zone to 30cm is key to getting the next productivity increase for agriculture,” she said.
“We know that in a zone like the SE, even in a dry year there is water in the profile at harvest and we just have to encourage the roots to get there.”
At each of the three New Horizon sites at Brimpton Lake, Karoonda and Cadgee, a range of treatments have been tested from shallow clay disced to 10cm, to organic matter such as lucerne hay.
The combination of spading, clay, organic matter and nutrition had the largest cumulative biomass response across the three years at all sites, with grain yields almost doubling in dry years.
At Brimpton Lake grain yields – in a wheat-wheat-barley rotation – increased by 3.6 tonnes a hectare when organic matter was spaded in, compared with the control, which was managed to district practice.
The greatest increases were seen in 2014 and 2015, when the annual rainfall was 100 millimetres less than the long-term average.
“In years that rely on accessing subsoil moisture and nutrients, that’s where the treatments pay off with at least 1t/ha increases,” Dr Fraser said.
Each sandy soil has a different set of challenges.
At Karoonda, an extra 3t/ha was harvested in the wheat-wheat-peas rotation and at Cadgee the response was 1.4t/ha, for seasons of wheat and then barley.
The 2016 canola crop at Cadgee was badly damaged by birds at maturity and unable to be harvested.
These results confirm the benefits of spading and clay spreading to improve SA’s estimated 2.1 million hectares of sandy soils.
But Dr Fraser believes incorporating organic matter will also be key to prolonged amelioration benefits, by either using manures, compost or a “cut and carry crop”.
“We know we can grow a 5-6t/ha crop of vetch or some other hay crop, if not in that paddock then somewhere else on the farm, and cut it and put it into their sandy soils,” she said.
Seven additional sites are being established across SA, NSW and Vic under the GRDC Sandy Soils project, with collaboration from the CSIRO, UniSA, PIRSA, Mallee Sustainable Farming and AgGrow Agronomy.
The three existing PIRSA sites will continue with their 11 treatments until 2019 and a fourth site will be established with UniSA at Murlong on the EP, which will characterise soils and explore yield responses, using different soil wetting agents and mechanical treatments.
This includes using a ripping tyne to break soils with high bulk density and inclusion plates to get top soil down into the profile.
Dr Fraser says farming groups will be involved in testing the different “treatment packages”.
“Each sandy soil has a different set of challenges,” she said. “Ultimately it is about improving water use efficiency, but we are confident we can make the treatments pay.”