Increasing the clay content of sandy soils in the Great Southern region of Western Australia can reduce soil erosion risk by improving crop establishment, potentially increasing crop yields.
A soil erosion management project was conducted in 2015-16 by North Stirlings Pallinup Natural Resources at five sites south of Borden to demonstrate the effect of applying clayey subsoil to sandy duplex soils. Trials Coordinator Laura Page said that 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. All the sites have sandy surface soil that is prone to blow in dry autumn conditions before the new crop can get established. Poor crop germination leaves the soil exposed to further erosion.’
Research has shown that the susceptibility of a soil to non-wetting is very low if the clay content is greater than 5%1. ‘The aim of the project was to use clayey subsoil sourced from the immediate area to increase the clay content of the topsoil to around 5%,’ she said. ‘Post-treatment soil testing showed that the treatment had increased the clay content of the topsoil, and that this was maintained into 2016.’
‘The farmers involved in the project reported reduced blowing of exposed soil at the demonstration sites in the dry autumn of 2015. However, crop yield depends on the soil that the plant roots have to explore throughout the season. On the deep sands, there is low water- and nutrient-holding which ultimately limit the yield potential of the crop.’
‘Head counts were made before harvest as a way of estimating final yield,’ she said. ‘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 showed the most topsoil erosion prior to the claying treatment. 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.’
In 2016 monitoring of the sites continued, and there were slightly better plant populations 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.
Local farmer Murray Moir has found at his demonstration site that the addition of clay increased the effectiveness of rainfall. “If we get 10mm of rain on our coarse sand soil, it sometimes doesn’t last long enough for pasture seeds to germinate and get going.” Murray has seeded canola into the clayed area this year, and found that although the crop was a bit slow to get going compared to the non-clayed part of the paddock, it has taken off in the last week. “We have found that it is important after applying the clay to work the clay in well.”
The project suggested that potential yield response to applied clay was greater on the visibly eroded site. Claying is a relatively expensive alternative to address soil non-wetting, and on sites without visible erosion, other options including wetters and changing the seeder bar are worth considering. Other soil issues that may restrict yield also need to be addressed.
This project is supported by North Stirlings Pallinup Natural Resources, through funding from the Australian Government’s National Landcare Programme.
North Stirlings Pallinup Natural Resources is a not-for-profit group covering a large parcel of the Pallinup River catchment area bound by the Shires of Gnowangerup, Broomehill and Tambellup in Western Australia. Our aim is to inspire both current and future generations to undertake sustainable management of the regions natural resources through coordination, education and implementation programs. We ensure all information and technology presented to our members is up to date and delivered by professionals and experts in their field. As a highly motivated group of people we seek to encourage the viability of the landholder by forging connections with other environmentally related fields to benefit the social, economic and environmental status of the North Stirlings Pallinup areas.
1 Davenport, D. et al (2011) Spread, delve, spade, invert: a best practice guide to the addition of clay to sandy soils. Grains Research and Development Corporation. p5
For more media information including photos:
Laura Page, Trials Coordinator, North Stirlings Pallinup Natural Resources
mob 0401 553 285 08 9828 1086 (BH) 08 9828 1159 (AH)