The effect of cover crop species on growth and yield response of tree seedlings to fertiliser and soil moisture on reclaimed sites

Abstract

Several grass species are being screened to identify appropriate cover crops for stabilising recently reclaimed oil sands sites and for nursing newly planted tree seedlings on these sites. Besides soil erosion control, cover crops can influence the establishment success of tree seedlings by regulating the impacts of nutrients, moisture, and light on early survival and growth. However, interspecific interactions determining the net effects of these resources on tree seedling establishment in the Oil sands region are poorly understood. This study evaluated growth and yield responses of trembling aspen (Populus tremuloides) and white spruce (Picea glauca) seedlings to fertiliser, soil moisture, and cover crop species using the bioassay factorial experiment. The objective was to characterise the effects of interspecific interactions on growth of tree seedlings. Barley (Hordeum vulgare) and oats (Avena sativa) were used as test crops because these herbaceous species are being recommended for oil sands reclamation operations. Significant height and root collar diameter (RCD) growth increments of tree seedlings after fertilisation were attributed to differential growth rates between tree species. In contrast, soil moisture stimulated height, shoot and root biomass yields of tree seedlings. Cover crops species largely controlled growth and yield responses of tree seedlings to fertiliser and soil moisture. Even with fertilisation, RCD increment and shoot biomass yield were reduced by 26–51% and 36–68%, respectively, relative to the no grass treatment (grass control). These effects increased with increasing fertiliser and moisture levels, indicating enhanced access to growth resources by tree seedlings after alleviating interspecific competition. Comparatively the suppressive effect of barley was higher than that of oats probably due to a combination of vigorous growth and possible allelopathic effects. Apparently, weed competition may adversely affect early growth and yield of tree seedlings on reclaimed oil sands sites by inducing or augmenting the effects of nutrient limitation and moisture stress. However, revisiting fertiliser recommendations to account for nutrient uptake by the competing vegetation may be the appropriate approach for enhancing tree seedling growth in the oil sands region because cover crops are planted for stabilising recently reclaimed sites. This approach, however, need to consider the observed species-specific response to weed competition.