Study shows clay protects post-fire soils

News release
26 August 2019

clay spreading across a burnt paddock at Barabba - credit David Woodard

Clay spreading across a burnt paddock at Barabba - photo David Woodard 

A project which examined clay spreading in very sandy areas of the Lower North region of South Australia has demonstrated both short and long-term benefits for crops as well as helping protect against future fire damage.

Nicole Bennett, who is Sustainable Agriculture Team Leader with Natural Resources Adelaide and Mt Lofty Ranges said the project was prompted by the devastating Pinery fire in November 2015, which stripped the surface protection from 85,000 hectares of cropping land and exposed it to serious wind, dust and soil erosion.

“Following the fire, many growers tilled their paddocks to roughen the soil surface with soil ‘clods’, in order to reduce wind speed and soil movement. This was relatively successful on heavier soils such as loam and clay, but the sandy soils and sand hills continued to drift,” Ms Bennett said.

“Clay spreading is used to improve the structure and water-holding capacity of deep sandy soils, and so a project was quickly set up to test the benefits.”

Benefits

Ms Bennett said 50 monitoring and five spreading sites were set up in Pinery, Barabba and Stockport in order to test the benefits of clay spreading, which were previously known to improve structure and water-holding of deep sandy soils. Where possible, clay from the paddock being treated was used. The clay was excavated, spread over a sandy area and incorporated into the soil, based on experience in areas such as Eyre Peninsula.

Monitoring was carried out for nutritional and biological characteristics, and to compare burnt and unburnt areas. Field days were organised so local landholders could watch these processes and learn more.

“The benefits of clay spreading were seen immediately, in the form of reduced wind erosion,” she Ms Bennett said.

“When rain arrived in autumn, there were visible improvements in sand-wetting qualities, crop emergence and consistency of crop establishment. One Barabba landholder commented that he had ‘never seen a crop like that on that area before’.

The 2016 season featured exceptional growing conditions, leading to record yields in many areas as well as high stubble loads to protect the soils in the later years, by promoting nitrogen and carbon cycling to restore soil biological health.

Monitoring showed that loss of soil nutrients from the fire was lower than initially feared. Where growers had maintained good soil health before the fire, losses were minimal.

One site at Linwood tested the long-term effects of clay spreading, with a sandhill being clay-spread five years before it was burnt by the fire. There was minimal erosion after the fire, and the clayed area showed 80 per cent higher cation exchange capacity (CEC), a measure of soil fertility, and improved availability of phosphorus, potassium and nitrogen.

“Overall the results demonstrate the benefits of well-maintained soil health in improving resilience, and the long-term benefits of clay spreading,” Ms Bennett said.

The clay spreading project was supported by Primary Industries and Regions South Australia (PIRSA) and the Adelaide and Mt Lofty Ranges NRM Board through funding from the Australian Government’s National Landcare Program and the NRM levy.

Rural landholders can access regular practical advice and technical information by subscribing to Small Talk, published by Natural Resources Adelaide and Mt Lofty Ranges. Phone 8273 9100

 

 

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Natural Resources Adelaide and Mount Lofty Ranges