INCREASING the clay content of sandy soils in the Great Southern could reduce soil erosion risk by improving crop establishment, according to a project by North Stirlings Pallinup Natural Resources (NSPNR).
Funded through the Federal Government's national Landcare program, the soil erosion management project conducted in 2015 and 2016 at five sites south of Borden demonstrated the effect of applying clay subsoil to sandy duplex soils.
NSPNR trials co-ordinator Laura Page said in 2015 the clay application generally caused a slight improvement in the plant germination rates of the subsequent crop by improving the ability of the surface soil to absorb and hold moisture.
"The five sites selected for the claying demonstration were chosen due to lower crop productivity, which was in part attributed to the negative impact of non-wetting soil on plant germination," Ms Page said.
"All the sites have sandy surface soil that is prone to blow in dry autumn conditions before the new crop can get established and poor crop germination can leave the soil exposed to further erosion."
Ms Page said research had shown that the soils were less susceptible to non-wetting issues if clay content was greater than five per cent.
"The aim of the project was to use clayey subsoil sourced from the immediate area to increase the clay content of the topsoil to about 5pc," she said.
A subsoil clay pit was opened with a bulldozer, with the subsoil material applied with a carry-grader in strips at about 200 tonnes per hectare.
The clay was then spread across the soil surface with a smudge bar before being incorporated with discs or a scarifier.
A no-clay control strip was also left for comparison.
Ms Page said following the treatment, soil testing showed that the clay content of the topsoil had increased.
She said the farmers involved in the project reported reduced blowing of exposed soil at the demonstration sites in the dry autumn of 2015.
She said some of the sites had also shown an increase in seed heads prior to harvest.
"At one site, there were more seed heads and more seeds per head where the clay was applied as compared to the control. This site had also showed the most topsoil erosion prior to the claying treatment," she said.
"However, at the other sites the claying had no or a slight negative effect on head count, which might be attributed to the clay holding tightly to soil water."
The project continued this year, with slightly better plant populations recorded where the clay was applied compared with the control at most of the sites.
"This was despite the wet season greatly reducing the impact of the non-wetting soil," Ms Page said.
Local farmer Murray Moir has found at his demonstration site that the addition of clay increased the effectiveness of rainfall.
"If we get 10 millimetres of rain on our coarse sand soil, it sometimes doesn't last long enough for pasture seeds to germinate and get going," Mr Moir said.
This year, Mr Moir has seeded canola into the clayed area and has found that although the crop was slow to get going compared to the non-clayed part of the paddock, it has taken off in the past two weeks.
"We have found that incorporation is important after applying the clay," he said.
Ms Page said the project suggested that potential yield response to applied clay was greater on the visibly eroded site.
She said at $600-650/ha plus fuel, claying was a relatively expensive alternative to address non-wetting soil and on sites without visible erosion, other options including wetters and changing the seeder bar should also be considered.
