Rainfall puts Hawker revegetation trial to the test

Cultivator strips were ripped to a 15cm depth to improve water infiltration across a six-hectare plot at Saul Webb and Louise Watson’s property in July last year.

After rain, the benefits were clear. Moisture reached just 15cm on hard, scalded surfaces, but on the adjacent cultivated strips, moisture was measured at a depth of 50cm. 

Most early growth came from coloniser species, many of them introduced rather than native; with the strongest plant growth occurring in cultivated areas. 

This is expected given the site’s cropping history. The early growth will stabilise the surface and build soil organic matter and will be gradually replaced by perennials. 

More than four kilograms of locally sourced native seed mix was direct seeded last year. With the site fenced to exclude grazing pressure, growth of these plants will return organic carbon to the soil and reduce the risk of the surface re-sealing. 

There is a higher level of recruitment in lines that have been ripped or pitted, over those that have had no intervention. This is due to surface capping, which results in water run off more than in vegetated areas. 

Rockville’s revegetation site has predominantly heavy clay and clay loam at the surface, with a sandy and sodic subsoil. Creating disturbance like ripping or scalloping worked well to revegetate these soils, however it’s not the only way to create disturbance. 

Additional benefits from re-seeding have been erosion control. An active gully in the central-western part of the plot has slowed significantly and root and leaf cover are beginning to slow the flow of surface water after rainfall events.  

This is also expected to reduce erosion impacts caused by water running off hills adjacent to the property. 

The trial underway is designed to improve groundcover and build a perennial seed bank of locally-suitable native species. The perennial native pasture is expected to better handle summer storms and extreme weather than cropping. 

The costs and methods used in the trial are being recorded and once complete, a best-practice revegetation guide for the SA Arid Lands will be developed. The findings will be shared with the wider community. 

The Building Pastoral Sustainability project is supported by the Australian Government through funding from the Natural Heritage Trust under the Climate-Smart Agriculture Program.