Renovation of wastewater by a short rotation intensive culture hybrid poplar plantation in Vernon, B.C.

A three-year study in Vernon B.C. considered the effects of two levels of wastewater irrigation on tree growth, nutrient uptake rates by the foliage and wood, nutrient leaching, and chemical properties of soils in a short rotation intensive culture (SRIC) hybrid poplar plantation where fourteen different clones were planted in separate subplots in a 5-ha area. Wastewater irrigation levels were determined on the basis of the calculated values of the local monthly potential evapotranspiration (ETp). In the first year, all plots received almost equal amounts of wastewater. In the second and third years, treatment 1 and the freshwater (control) plots were irrigated at the rate of ETp + 30%ETp. Treatment 2 received approximately twice this amount. The effect of wastewater irrigation on increased height, basal diameter, total leaf area, leaf biomass and woody biomass was measured as early as the end of the first growing season. During the third year, woody biomass production of the plantation was 11, 20, and 24 Mg/ha for control, treatment 1 and treatment 2, respectively. Concentration of N,P, and K in the foliage of wastewater irrigated trees increased significantly in the third year. Nutrients in the soil solution were monitored in samples from suction lysimeters. In the first growing season, concentrations of N, P, K, in soil solution were significantly higher than in the following two years. This was attributed to cultivation of the land at the time of establishment of the plantation. At the end of the third year, concentrations of N and P in the foliage of wastewater-irrigated plots were higher than in the freshwater plot. Other nutrients remained unchanged in different irrigation treatments. Soil N, P, Na and Mn decreased while K, Ca, Mg, Zn, Cu and Fe remained unchanged from 1988 through 1990. Efficiency of the soil-plant system in removing nutrients added through wastewater was: N, 97% and 95%; P, 97% and 94%; K, 40% and 0%; Na, 12% and 0%; Mn, 79% and 66%; Zn, 93% and 80%; Cu, 100% and 100%; and Fe, 100% and 92%; for treatments 1 and 2, respectively. Because of the high concentrations of Ca and Mg in the soils, removal efficiencies of these elements were not measurable. Nutrient uptake rates by the woody biomass were N, 71% and 42%; P, 29% and 20%; K, 50% and 33%; Ca, 21% and 14%; Mg, 8% and 5%; Na, 0.6% and 0.5%; Mn, 46% and 36%; Zn, 78% and 70%; Cu, 18% and 4%; and Fe, 30% and 22% for treatments 1 and 2, respectively. Based on these data, it was concluded that the optimal wastewater irrigation level for the plantation in the first three years would be treatment 1 (1.3 x ETp), where nutrient uptake levels by woody biomass and nutrient removal efficiencies were higher than for treatment 2 (2.6 x ETp), therefore the groundwater contamination level would be lower.Forestry, Faculty ofGraduat