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Topsoil Deficits in Site Rehabilitation Accelerated Transformation of Spoils to Functional Soils

Open Cut » Environment

Published: November 23Project Number: C28035

Get ReportAuthor: Guilherme da Silva, Samadhi Gunathunga, Paul Evans, Peter Erskine, Emma Gagen and Gordon Southam | The University of Queensland

The incorporation of commercial biological amendments (compost, worm juice and dried manure) and topsoil at a Bowen Basin coal mine site over a 12 month field experiment increased early microbial enzyme activity (β-glucosidase, cellobiohydrolase, urease, phosphatases) compared to gypsum + mulch amended spoil. However, long term improvements were not observed. Interestingly, the application of 10 cm versus 20 cm of stockpiled topsoil to spoil produced comparable results demonstrating that the application of topsoil can double the conventional coverage area.

The greenhouse trial, which employed two water regimes, matching optimal irrigation and average Bowen Basin, rainfall (2000-2020) demonstrated improved plant growth under optimal irrigation conditions compared to the site rainfall simulation, suggesting that the drought conditions of the mine site are a limiting factor for a successful rehabilitation when an irrigation system is not in place.

The second field trial employed an unamended spoil, that had not received any treatment, i.e., gypsum or mulch, other than contouring. Self seeding of unamended spoil at the field site produced extensive plant, i.e., Pigweed (Trianthema sp.) and Sesbania sp. coverage in a short, six month field trial. Plants were not widely observed elsewhere on the contoured spoil, demonstrating that mulch and site specific biofertilizers improved early stage, technosol formation, i.e., plant growth and biogeochemical cycling. The addition of site-specific biofertilizers increased the metagenomic diversity of both the greenhouse and field ecosystems.

None of these short term, seasonal experiments produced improved physicochemical conditions. The high pH, electrical conductivity, spoil sodicity, and low organic matter remained the driving factors that shaped short term soil fertility.

The enzyme activities in unamended spoil, without any treatment, gradually improved over time and became comparable to, or better than the biological amendments or topsoil induced spoil-to-soil transformation.


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