Impact of single and combined soil amendments on the growth and foliar nutrients of white spruce (Picea glauca) on a poorly regenerated logged site.

Regeneration failure is occasionally encountered in the boreal mixed forest following clear-cutting, primarily due to competing vegetation and altered soil conditions. This study investigates the effects of applying several soil amendments to improve white spruce plantation growth on poorly regenerated forest sites. Biochar (2.6 Mg ha-1), wood ash (7 Mg ha-1), and manure (105 Mg ha-1) were used alone or in combination, with effects on foliar elements and seedling growth assessed after two growing seasons. While biochar and wood ash have been frequently used, combining them with manure has been limited in boreal forests. Using a randomized complete block design, we measured soil pH, incident light, seedling growth, specific leaf area, and foliar nutrition. Manure significantly increased seedling growth (+37%) compared to treatments without it. It also increased foliar nitrogen (+17%) and phosphorus (+14%). Wood ash increased foliar nitrogen (+7%), phosphorus (+15%), potassium (+19%) and calcium (+29%). Biochar, without wood ash, decreased foliar aluminum by 56%. We conclude that manure represented an important nitrogen and phosphorus source for seedling growth. This research highlights the potential of amendment combinations for improving growth and foliar nutrition of seedlings in poorly regenerated boreal forest ecosystems, for example where herbicide use is prohibited.