Suncor Energy is in the process of reclaiming one of its consolidated tailings ponds (Pond 5). Tailings sand is known to have low available water holding capacity and usually lacks organic matter and nutrients. A peat/mineral amendment is typically used to mitigate such limitations. Rather than using stockpiled soil in the establishment of the temporary cover (and potential lost to future use), an alternative amendment was desired. We speculated that native plants can thrive on tailings sand, provided a good nutritional program is developed to sustain plant growth.
The overall goal of this research was to evaluate the possibility of establishing a temporary reclamation cover on tailings sand, using various cover crops and different levels of Western Alfalfa Milling's Alfalfa Green pellets as an amendment. Nitrogen fertilizer was also added at a rate of 50 and 250 kg/ha to provide the necessary nutrients for the plants. Plant species selected for this research include two cultivated annuals: barley (Hordeum vulgare) and oats (Avena sativa), two native perennials: fringed brome grass (Bromus ciliatus), June grass (Koeleria macrantha), and a mixture of native grasses and one cultivated species: oats (Avena sativa), slender wheatgrass (Agropyron trachycaulum), Rocky Mountain fescue (Festuca saximontana), spike trisetum (Trisetum spicatum), June grass (Koeleria macrantha), fringed brome (Bromus ciliatus), Canada wild rye (Elymus canadensis), and tufted hair grass (Deschampsia caespitosa). The suitability of alfalfa pellets as a soil amendment to provide plant nutrients, improved soil structure and moisture retention was also evaluated.
First year observations showed remarkable growth of native species on tailings sand. There were no significant difference in plant heights and plant cover between plots that received pellet applications of 5, 10 and 20 t/ha. The amount of total available nitrogen did not differ between rates of alfalfa pellet applications or between fertilizer rates. In addition, the species did not differ in terms of the amount of total available nitrogen. There was no difference between the fertilizer rates in terms of total N in roots and shoots. Despite the shorter plant height and lower vigour of the fringed brome grass and June grass compared to barley and oats, the native grasses had greater uptake of nitrogen, which could probably be due to their extensive root development. Furthermore, the native grasses are perennial and have potential to provide adequate cover against erosion for a longer portion of the year and even in subsequent years.
The application of alfalfa pellets at the minimum rate of 5 t/ha improved bulk density of tailing sands, but to a lesser extent than the maximum rate of 20 t/ha. Alfalfa pellets incorporated into the tailings sand
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appear to have better moisture compared to no pellets. The short growing season did not allow full realization of the benefits of the alfalfa pellets and fertilizer application. It appears that most of the nutrient applied has been lost to the environment. A split time application of fertilizer would have been most beneficial to the plants.
The study demonstrates the potential of native species for tailings sand stabilization against water and wind erosion for a temporary reclamation area on Suncor Pond 5. However, the results presented here should be treated as preliminary and interpreted with caution pending additional data and validations in subsequent years.