Survival and growth of tree seedlings on reclaimed oil sands site in response to fertilizer and ground cover grass species
Every year, oil sands mining results in a significant area of degraded land which needs to be reclaimed. In reconstructed mine sites, ground cover is helpful to minimize soil erosion by stabilizing soil. Besides soil erosion control, ground cover may also influence the establishment success of tree seedlings by affecting soil nutrient and moisture availability. Barley (Hordeum vulgare L.) and oats (Avena sativa) are the ground cover species being recommended for oil sands reclamation operations, but interactions of the ground cover with planted tree seedlings are not fully understood. The objective of this study was to evaluate the effect of different fertilizer rates on survival and growth of trembling aspen (Populus tremuloides) and white spruce (Picea glauca) tree seedlings planted with two cover crops (barley and oats). To fulfill the objective a greenhouse bioassay experiment and a field experiment were conducted. Under greenhouse conditions, soil moisture significantly increased height, root collar diameter (RCD) and biomass yield of tree seedlings. Fertilizer application significantly increased height and RCD in greenhouse, but not under field conditions. Even without ground cover competition, tree seedlings responded poorly to NPK fertilizer. Furthermore, survival rates of tree seedlings were significantly decreased with increased fertilizer application rates, and no positive growth and yield responses were observed in the field. Vigorous growth of ground cover species with high fertilizer application rates largely controlled survival and growth responses of tree seedlings. Trembling aspen was more sensitive to ground cover competition and negatively affected by barley and oats with added fertilizer, whereas white spruce was unaffected. Therefore, adding fertilizer to these systems appears to be of little benefit to early establishment and growth of tree seedlings as well as for successful reclamation.
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