Centre for Plant & Water Science - Central Queensland University

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Centre for Plant & Water Science 2008 Annual Report NATIVE GROUND COVER SPECIES FOR REVEGETATION UNDER HIGH VOLTAGE POWERLINES IN QUEENSLAND SUMMARY The practice of using tubestock in revegetation programs is becoming very popular. However, records of very low plant survival have been reported in such revegetation programs. Survival of plants in revegetated sites largely depends on how well the potting mix allows the water to enter into the root zone during establishment stage. This character is determined by the physical and chemical properties of potting media used in raising the seedlings. Forty one commercially available potting media that were sold in the markets were therefore tested along with two soil samples for their lack of ability to attract water from surrounding environment, the hydrophobicity. By using the Water Droplet Penetration Test (WDPT), hydrophobicity of those media was determined and the media categorised into five classes. Out of 43 media tested 28% of the media were classified as extreme, 35% as severe, 21% as strong, 11% as slight and 5% as non-hydrophobic. Construction of powerlines in Queensland is increasing at the rate of 3.4% per annum, to service increasing demand of electricity for various developmental activities such as mining, agriculture, industries, beef production, smelting and tourism. Extending the powerlines means more tree clearing or disturbance of already existing and adapted vegetation in the extended areas. The clearance of the existing plant communities greatly accelerates the process of soil erosion, loss of biodiversity and the rate of spread of invasive weeds. For revegetation of such degraded landscapes, a few exotic species have been used at high costs. Due to their invasive nature these species have gradually replaced valuable native biodiversity. As these powerlines pass through diverse bioregions of Queensland, use of exotic species in revegetation will not be a meaningful solution. Therefore, the proposed project will identify native ground cover species for successful revegetation of land under high voltage powerlines. The study will also develop suitable agronomic practices for survival and long term sustainability of established species. The most critical stage in revegetation program is the establishment phase. Use of nursery raised seedlings has become very popular in revegetation programs. Seedlings are mostly established in the rainy season with or without irrigation. Plant survival rate in such activities is very low and has negatively affected the revegetation program significantly. In nurseries, seedlings are raised in different potting media. The nature of potting media used in the nursery affects the ability of plants to extract available moisture from the surrounding soil once they are transplanted in the field. To determine the hydrophobic properties of media, we purchased 41 commercial media from shops in Rockhampton. Two soils (black and red) were also used as controls. By using the Water Droplet Penetration Test (WDPT), the degree of hydrophobicity of collected media was determined. Three drops of deionised water were placed on top of potting media at 1 cm apart (Fig 1). The time taken (in seconds) for the water drop to penetrate the media was recorded (Lal and Shukla 2004). Based on this time, the media were categorised into the following groups. 36000 seconds: extremely hydrophobic Results (Fig 2) show that all potting media were hydrophobic to some degree, and the only two media that had no hydrophobicity were the two soils (black and red) that were used as controls (5% of the tested media). More than 50% of the media tested were severely to Page 51
Centre for Plant & Water Science 2008 Annual Report extremely hydrophobic indicating that extra care must be taken in choosing potting media for revegetation programs, particularly when the transplanted seedlings are not watered regularly, or when they rely upon rainfall. This is because moisture content of the potting media in which the seedlings are raised will decline due to water use by the seedling and evaporation. This drying of potting media triggers hydrophobicity to such an extent that it will prevent movement of water from the surrounding soil into the potting media. The resulting situation ultimately results in either slow growth of the seedling or eventual loss of the plant. The ability of the plant to send roots into surrounding soil plays a critical role in their survival. Since native plants are slower at this than crop plants, many native plant seedlings do not respond as quickly as the media dries out. In field situations, where revegetation practitioners do not have any control on irrigation or soil moisture content, choosing a potting medium that is less likely to become hydrophobic when the soil moisture declines, will enhance the survival rate of transplanted seedlings. Figure 1. Droplet test used to determine hydrophobicity of potting media Figure 2: Percentage of tested media showing different degrees of hydrophobicity *Lal, R and Shukla, M (2004). Principles of soil physics. Marcel Dekker Inc, New York, 2004. Pp 716. PROJECT STAFF Principal Investigator: Co-Principal Investigator: Others: FUNDING Powerlink INCOME $135,000 Resham Gautam A/Prof. Dr N. Ashwath Prof. Dr D. Midmore Page 52
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Centre for Plant & Water Science - Central Queensland University

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