Growth, biomass production and nutrient accumulation by seven tree species irrigated with municipal effluent at Wodonga, Australia

In the Murray-Darling basin, irrigation of tree crops is being evaluated as an alternative method for the disposal of municipal effluent. A study was carried out at Wodonga in which seven tree species were irrigated with effluent for a period of 4 years. Irrigation was calculated weekly on the basis of pan evaporation and rainfall during the preceding week. Annual irrigation varied between 1190 mm and 1750 mm with a total input over the 4-year-period of 4940 mm.

Height and diameter growth varied significantly between species. At age 4, mean dominant height of Eucalyptus grandis, E. saligna and Populus deltoides × P. nigra ranged from 14.3 to 15.0 m compared with 6.6 to 9.8 m for Casuarina cunninghamiana, E. camaldulensis, P. deltoides and Pinus radiata. Wood production of the faster-growing species (E. grandis and E. saligna) was approximately 130 m³ ha^?1, or around 32 m³ ha^?1 year^?1 over a 4-year period. This was nearly three-fold the production of the other native species and twice that of Pi. radiata. Volume growth of P. deltoides × P. nigra (85 m³ ha^?1) was significantly greater than that of P. deltoides (42 m³ ha^?1).

Accumulation of nutrients in the above-ground biomass varied significantly between species and ranged from 24 to 41 g m^?2 for N, 2.6 to 5.9 g m^?2 for P, 0.5 to 9.2 g m^?2 for Na, 12 to 27 g m^?2 for K, 7 to 52 g m^?2 for Ca and 3.1 to 7.9 g m^?2 for Mg. Nutrient accumulation was generally greater in species with a comparatively large crown biomass relative to stem size such as C. cunninghamiana and E. camadulensis. Average nutrient accumulation by trees as a percentage of input from effluent was estimated at 19% for N, 9% for P, 1% for Na, 14% for K, 52% for Ca and 32% for Mg.

Results of this study indicate the importance of selecting species on the basis of not only growth but also nutrient accumulation to optimise renovation of wastewater by tree plantations.