Use of Soil Amendments to Maximise Wood and Carbon Values from Trees Planted on Overburden and Buffe

Since the Kyoto Protocol was first drafted in 1997, many companies have started to investigate the options available to reduce their greenhouse gas emissions and address the threat of climate change. One popular emission reduction strategy involves the establishment of tree plantations to sequester carbon from the atmosphere back into living plant tissue. Plantation establishment is often favoured because it may also provide financial returns, in the form of saleable timber products and/or tradable carbon credits. In the Hunter Valley (in NSW, Australia) there is also interest in investigating alternative/supplementary industries to coal mining.  However, since commercial growth rates had not, until now, been clearly demonstrated in the Hunter Valley, mining companies have been reluctant to embrace timber plantations.  

Mines have an obligation to rehabilitate after the mining process. The Upper Hunter Valley has approximately 20,000 ha of land requiring rehabilitation.  Due to the nutrient poor nature of the unconsolidated overburden, considerable time and money is spent getting the nutrient cycling process started again.  It was thought that soil amendments, such as biosolids, may assist in this process and may make the eucalypt plantations a viable alternative to traditional use of pasture in rehabilitation. The Upper Hunter Commercial Forests Steering Committee identified a need to coordinate an integrated investigation into the viability of commercial plantations in the Hunter.  This research directly addresses the key priorities identified by the Working Party.

1. Determining timber yields on a range of sites
2. Determining the most appropriate plantation species
3. Assessing the role of soil ameliorants (such as biosolids and other organic wastes)

This research program investigates the role that soil amendments (including biosolids and bottom ash) have on the successful establishment, survival and growth of trees.  This includes assessing the impact of fertiliser (organic and inorganic) on tree growth, nutrition and soil nutrition and moisture.

The series of 3 trials over 5 years included the assessment of Biosolids, Bottom Ash, inorganic fertiliser and various combinations of these residuals. Initially it was proposed to test coarse coal washery reject material (chitter) as a soil amendment, but since there were concerns regarding potential acid leachate from chitter, after consultation with industry monitors, bottom ash was used as an alternative structural amendment. The amendments have been assessed for their usefulness on reshaped overburden and undisturbed buffer land (the mandatory large area of land surrounding mines and power stations).  All trials are replicated block designs with split plots for species evaluation. In addition a species trial was established on the alluvial river flat to determine appropriate plantings for the area.

Historically, the most successful mine rehabilitation in the Hunter Valley has been back to pasture and often with annual applications of fertiliser for 5 years.  However, the rehabilitated land brings little return to the mining companies.  NSW DPI Science and Research has shown, in current trials, that trees can be established with a one-off application of Biosolids (not requiring expensive and repeat applications of fertiliser).  With the use of biosolids, good growth can be achieved on the overburden and buffer areas on mine land in the Hunter Valley, NSW, Australia.  In addition plantation trees provide a potential income from carbon credits, biomass, pulp logs or sawlogs and reach a sustainable end use earlier than alternative rehabilitation strategies.