The effects of growth medium acidity, exogenous growth regulators, and nitrogen fertilizer on the acceleration of Fraser fir seedling growth

Three factors were tested in an attempt to accelerate the growth of Abies fraseri seedlings grown in containers in a greenhouse: growth medium acidity. foliar application of growth regulators. and supply of nitrogen fertilizer.

Sphagnum peat growth medium was adjusted with a to 8 kg dolomitic limestone/m3 compressed packaged peat to initial pH ranging from 3.9 to 6.7. Best growth (21.2 cm mean height at 19 months) was achieved with 1 kg/m³ and 2 kg/m³â ¢ with initial mean pH 4.2 and 4.5. respectively. Seedlings with 4 and 8 kg/m³ grew more slowly (17.4 and 9.5 cm. respectively. in 19 months). and many were chlorotic. with poor root development.

Three growth regulators were sprayed on seedlings: benzylaminopurine (BAP). gibberellic acid (G~. and indolebutyric acid (IBA). BAP stimulated terminal bud activity. decreasing the periods of rest between active growth. BAP increased height and diameter of new shoot growth up to 19% and 32% respectively. BAP reduced root growth 22% when applied at the higher concentration (100 ppm). GA3 had no main effect on either shoot or root growth. However. GA3 did increase shoot growth slightly in the absence of BAP. IBA increased root growth up to 26%. IBA had no significant effect on shoot growth.

Nitrogen fertilizer was supplied weekly in concentrations of 200. 400. and 600 ppm. At six months age there was no treatment effect on seedling growth. At nine months age 400 ppm N had produced 9% more shoot growth than either 200 or 600 ppm N. Nine-month-old seedlings with 400 ppm fertilizer averaged 8.9 cm in height.