Fertilization at planting influences seedling growth and vegetative competition on a post-mining boreal reclamation site

Reclamation of post-mining sites is challenged by limiting factors including adverse soil chemical and physical properties, along with weed competition. Fertilization may alleviate nutrient deficiencies, but broadcast fertilization with immediately available fertilizers (IAF) results in generally low rates of nutrient recovery for planted trees. Directed application of controlled-release fertilizer (CRF) to the rhizosphere offers an alternative to extend nutrient longevity while reducing nutrient leaching or uptake by competing vegetation. We evaluated white spruce (Picea glauca (Moench) Voss) and aspen (Populus tremuloides Michx.) development on a mine reclamation site in the Oil Sands Region of northern Alberta in response to IAF and polymer-coated CRF (3–4 and 8–9 month release). IAF and CRF (each NPK plus other macro- and micro-nutrients) were applied at 20 and 40 g N seedling−1 and 2 and 4 g N seedling−1, respectively. No effect on seedling survival occurred. White spruce year-1 height and diameter growth responded positively to both IAF and CRF relative to non-fertilized controls, but in year-2 seedlings treated with CRF (i.e., 8–9 month) outperformed those fertilized with IAF, which were similar to controls. Aspen height growth did not respond strongly to fertilization in either year, but diameter growth showed positive responses to all fertilizer treatments in year-1 and to all CRF treatments and the high IAF rate in year-2. Responses were attributed to a pronounced increase in vegetative competition observed for IAF relative to CRF or controls following the first growing season, and generally higher levels of foliar N in year-1 for CRF compared to IAF or unfertilized trees. Thus, directed root zone application of CRF promoted seedling growth responses similar to or better than those induced by broadcast IAF applications, but at 90–95 % lower N application rates.