Since the 1970s, the minerals industry in the Hunter Valley has been looking for ways to rehabilitate mining operations to meet not only the increasingly high standards set by regulatory authorities, but to match the high expectations of the community. The mining process exposes thousands of tonne of nutrient-poor waste rock, subsoils and process wastes that have to be stabilised and revegetated. The Hunter Valley mines face further difficulties with reestablishment of vegetation due to low rainfall and poor quality topsoils in some areas.
In conjunction with the imperative for effective rehabilitation, is the need to find a viable and sustainable reuse option for green waste (and its derivatives). Green waste has been separated from the waste stream since 2001 and so offers a potentially valuable resource, in the right market. However unless this market is identified and adopted, the green waste, while separated, is not truly out of the waste stream. For these products to be used by industry there needs to be a commercial driver. This will come about if the product provides equal or greater benefits at a cost equal to or less than the current practices. It is important that this research identifies such uses. Public perception can also be a commercial driver.
The research program (funded by NSW Department of Environment and Conservation, NSW) investigates the role of various recycled organics in successful establishment, survival and growth of eucalypt plantations. The plantation was established in March 2004. The replicated block design trials 8 treatments: incorporated Biosolids (50 dry t/ha), surface applied Mulch (15cm), incorporated Soil Conditioner (80 dry t/ha), incorporated Municipal Waste Compost (MWC) (80 dry t/ha), standard Fertiliser protocol (100 g/tree NPK), Biosolids+Mulch, Fertiliser+Mulch and a control. The role that these soil amendments have in increasing tree survival and growth, maintaining soil moisture and reducing soil temperature, is being monitored. At the conclusion of the 3 year trial there will be a cost– benefit analysis.
After 12 months trees in plots treated with Biosolids, and Biosolids+Mulch exhibit the best growth (both height and diameter). These are closely followed by the Fertiliser+Mulch and Fertiliser treatments. The Soil Conditioner, Mulch and MWC treatments have growth rates comparable to the control. However, in the case of Soil Conditioner and MWC, survival is increased compared to all other treatments and growth rates are more consistent within these treatments.
The plots have been split to compare two eucalypt species, Corymbia maculata (spotted gum) and a clonal hybrid Eucalyptus camaldulensis*grandis (River red gum/flooded gum hybrid). Whist the species are growing at different rates, they are responding in the same way to treatment. Soil temperature is being assessed using fixed temperature probes (20cm depth). Mulch is proving the most effective in moderating soil temperature and moisture. The other organic amendments (Biosolids, MWC and Soil Conditioner) are moderating the soil temperature but not nearly to the same extent. Soil moisture is critical in the Hunter Valley, NSW. Average annual rainfall is 750mmm, but in the last few years 500-550mm annual rainfall has not been uncommon.
Soil moisture has been monitored using Time Domain Reflectometry and a Neutron Probe. The data to date show that Mulch is the most effective treatment in maintaining soil moisture. The initial data indicate that recycled organics can have a significant role in increasing tree growth and survival, and improving soil moisture loss thus making them a valuable resource for mine site rehabilitation. Monitoring will continue for the next two years during which time soil and foliage chemistry will be assessed.
KEY WORDS Recycled organics, biosolids, greenwaste, mulch, compost, municipal solid waste, rehabilitation, mines, plantation, forestry, fertiliser, soil moisture, nutrition.
