Effects of fertilization and liming on tree growth, vitality and nutrient status in boreal balsam fir stands

• Two fertilization trials were set up in young balsam fir stands.
• Potassium was the sole nutrient that increased tree growth over a decade.
• Soils properties were modified by liming; however it had no effect on tree growth.
• Nitrogen had only a short term effect on tree growth and foliar nutrient status.
• Potassium appears to be the main limiting nutrient in this boreal forest ecosystem.

Two fertilization trials were carried out in young balsam fir (Abies balsamea (L.) Mill.) stands showing symptoms of tree decline or foliar chlorosis in boreal forests of eastern Laurentian Highlands in Quebec, Canada. In the first trial, trees showed strong decline symptoms; fertilization treatments consisted of combinations of two nutrients among N, K, and Mg, each at two rates. In the second trial, trees showed some needle chlorosis; various doses of N, K, K–Mg, and K-lime fertilizers were applied. In both trials, N fertilization (200 kg N ha−1) resulted only in a short-term (2–3 years) increase in foliar N concentrations and radial growth. Potassium fertilization (100–400 kg K2O ha−1), however, led to an increase of at least 33% in both foliar K concentrations and radial growth, which lasted for the duration of the experiments (7–11 years). Liming (1–4 t dolomitic lime ha−1) increased the pH, exchangeable calcium and exchangeable magnesium in the humus and top mineral soil horizons, but did not influence balsam fir foliar nutrient status or growth. Tree defoliation rate was mainly related to growth decrease and foliar K concentrations. The trials also show that K was the most limiting nutrient for balsam fir growth, and that the poor K nutrient status and vigor of balsam fir trees can be corrected by K fertilization. These results contrast with past fertilization studies that generally reported N as the most limiting nutrient in these boreal ecosystems. Climatic events may have also played a role in triggering the decline of balsam fir in one trial.