Long-term recovery of scalded soils

Thanks to James Hunt, Sydney University, for supplying this short synopsis of his honours project and goals of his PhD project. Our Hay office staff worked with James to help identify sample sites for this work.

During 2020 I completed a pilot study that investigated the long-term recovery of scalded soils that form when erosion completely removes topsoil exposing saline-sodic subsoils.

These subsoils become impermeable to water because of the formation of self-sealing surface crusts. Low soil moisture makes it difficult for plants to recolonise scalds leaving the soils in a persistently unproductive state. In this study we compared the condition of scalds to uneroded soil and to scalds that had been reclaimed by ponding banks in the 1960’s and early 2000’s.

Ponding banks trap water allowing it to seep through the surface crust, which leaches salts down the soil profile, opening large cracks in the surface allowing vegetation to establish. The structural and chemical properties of scalds, reclaimed soils and uneroded soils near Hay were compared to determine the long-term effects that scalding and reclamation using ponding banks have on soils.

We found that even after more than 60 years scalded soils remained severely degraded with a self-sealing crust, high concentrations of salts near the surface and very low soil carbon concentrations.

In contrast, scalded areas that had been reclaimed by ponding banks had chemically and structurally recovered, becoming functionally analogous to the uneroded soils. However, our soil carbon recovery results for the reclaimed soil were inconclusive. This is most likely because of the sample sizes used in this initial study.

This pilot study formed the basis of a PhD research project which I am currently undertaking that will focus on assessing the potential of scald reclamation, through techniques such as ponding banks, to sequester soil carbon.

The aim of this project is to provide a strong scientific basis for using ponding banks to sequester soil carbon which will contribute to mitigating greenhouse gas emissions and provide an addition revenue stream or social licence to landholders through carbon credits.

To do this we will once again compare the chemical properties of uneroded soil, scald, and ponded soil to determine the increase in soil carbon after ponding. The rate of soil carbon recovery will also be investigated by sampling ponding banks of varying “ages” that have been constructed at different times.

Several ponding banks that were constructed by the Soil Conservation Service in the early 1960’s have had 60 years to recover while other ponding banks constructed in 2012 have only been recovering for a decade.

We will also investigate if there are any soil chemistry parameters that limit carbon sequestration. If limiting factors are identified, it means that they can be addressed to ensure maximum carbon sequestration.

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