Irrigation of tree plantations with wastewater in Victoria.  1. Site characteristics, establishment and maintenance procedures, and tree survival and growth, between 1977 and 1981.  H. T. L. Stewart, D. W. Flinn and P. J. Baldwin.  December 1982.  59 pp.  (unpubl.)

SUMMARY

This report records establishment and maintenance procedures, and tree survival and early growth rates, for trials established between 1977 and 1980 at five sites in Victoria, to evaluate the use of tree plantations for the renovation of wastewater and the production of forest produce. The trials were established in co-operation with Sewerage Authorities and industries at Mildura, Horsham and Merbein in 1977, at Robinva1e in 1979 and at Wodonga in 1980. The Reclaimed Water Committee of the Ministry of Water Resources and Water Supply provided research grants for the work throughout this period.

A total of 14 species from the genera Eucalyptus (eucalypts), Casuarina (she-oaks), Pinus (pines) and Populus (poplars) have been planted on a wide range of soil types and irrigated with winery wastewater at Merbein and with treated municipal wastewater at the remaining sites. Details of establishment procedures, including methods of site preparation, planting espacement, weed control practices and fertiliser application are given in detail for each site. Irrigation was applied using either spray, sprinkler or surface systems and, at two sites, was scheduled on the basis of estimated crop water use. Chemical characteristics of wastewaters are listed.

Effective weed control during the first two years after planting was found to be essential for successful establishment. Thereafter, most species planted at a relatively close spacing attained canopy closure. Weed control measures, including manual, chemical and mechanical methods, are outlined.

Significant insect damage has only been observed on river red gum (Eucalyptus camaldulensis Dehnh.), where populations of sawfly (Perga spp.) completely defoliated some trees less than two years old and caused less severe defoliation on older trees. The potential for widespread damage by insects to plantations of irrigated eucalypts is discussed. Wind damage has been observed at Mildura when trees aged 28 months were subject to a violent storm, with wind speeds of up to 110 km h^-1 being recorded; less than 2% of eucalypts were damaged, and reasons for this, as well as management procedures to minimise wind damage, are outlined.

With the exception of salt damage to Sydney blue gum (E. saligna Sm.) at Mildura, and foliar scorch to all eucalypts sprinkler-irrigated with winery wastewater at Merbein, no toxicity to tree growth due to the chemical characteristics of the wastewaters and soils has been observed. Iron deficiency was diagnosed and corrected in all eucalypts planted at Robinvale on a calcareous soil, and recommendations are given for the establishment of eucalypts on such soils. Foliar analyses indicated substantial uptake of nutrients from the applied waste-waters, and this was correlated with high growth rates. Frost damage significantly reduced initial survival at Mildura and Merbein, and some replanting was necessary.

On the basis of survival and growth at age four years, the most successful eucalypts have been flooded gum (E. grandis W. Hill ex Maiden), Sydney blue gum, river red gum and southern blue gum (E. globulus Labill.), though some species were found to be site specific and tree form for some was poor. Rapid growth rates were measured; for example, four-year-old flooded gum achieved a mean dominant height of 14 m, a mean DBHOB (diameter over bark at 1.3 m above ground level) of 11.6 cm and a mean annual increment (over bark volume) of 24 m³ ha^-1.

During the first 12 months after planting, radiata pine (Pinus radiata D. Don) grew at rates equivalent to those achieved on high quality sites elsewhere. Similarly, a deciduous and a semi-evergreen clone of poplar attained heights of 2.1 and 4.4 m respectively within 12 months of planting. River she-oak (Casuarina cunninghamiana Miq.) was found to be highly adaptable and grew well at all sites where tested.

As the production of useable wood products is an important objective of the trials, silvicultural treatment of fast-grown tree plantations is discussed, including pruning and thinning regimes. The successful establishment and early rapid growth of a number of tree species irrigated with wastewater underlines the potential for utilising tree plantations in wastewater management.

Also published:

Stewart, H. T. L. and Flinn, D. W.  (1984)  Establishment and early growth of trees with wastewater at four sites in Victoria, Australia.  For. Ecol. And Manage. 8: 243-56.