A NEW practise that aims to make friable topsoil from hostile subsoil in high-rainfall cropping zones is delivering yield benefits of up to 60 per cent.
These areas hold high yield potential but dense clay subsoils often limit crop performance.
Researchers from the Victorian Department of Primary Industries in conjunction with La Trobe University believe they have found the answer to breaking-up hard subsoil layers.
They are incorporating organic matter such as chicken manure at 40 centimetre to 50cm below the surface into the subsoil layer of duplex soils.
In the past six years, the soil has gained the ability to store more winter rainfall to be used later in the season, and roots which are generally restricted to upper soil layers have penetrated deeper.
Subsoil manuring is expensive, and requires relatively high rates, but results in more friable soil with smaller aggregates.
There are short-term nitrogen benefits as well.
It is now being trialled on a commercial scale in central Victoria at Ballan and validation trials have extended to South Australia.
Funding from the Federal Government's Caring for our Country program have seen two trials for Enhancing Soil Health in the South East of SA at Kybybolite and Joanna in the South East.
They will replicate the Victorian research and have buried lucerne pellets, gypsum, chicken manure and even sheep manure about 40cm below the surface.
Victorian DPI practice change scientist-soil and water Renick Peries, based at Geelong, says the practise of subsoil manuring evolved as farmers in high-rainfall areas were unable to reach the yield benefits they expected.
Raised beds had given some good results in water-logged soils but many crops were simply running out of moisture, especially during dry springs.
Along with another agronomist, Renick developed the Peries-Wightman subsoiler - a twin deep-ripper with the ability to put organic matter below the topsoil and about 5cm into the clay subsoil layer.
Early trials involved incorporating 5 tonnes a hectare of chicken slurry in these soils but with further research, they have recognised the need to lift this rate to 15-20t/ha.
Trials growing wheat, barley and canola on these manured soils in high-rainfall areas have shown yield increases up to 60pc and at least 10pc increase in water-use efficiency in the national water use efficency project.
"The end result has been a lot more porosity, improved capacity of the soil to take up water, a lot less waterlogging, and plants have been able to draw water from below the conventional root zone," Renick said.
He said the greatest benefit has been in years with dry springs.
"In 2009, there was a three-week heatwave in Victoria in November and we saw all the crops hayed off, except the manured plots which held on," he said.
GRDC has allocated funds for the project to validate the technology.
Renick said water-use efficiency was being monitored and that carbon sequestration and soil biology measurements would be undertaken subject to funding availability.
*Full report in Stock Journal, June 21 edition