Growth and nutrition of container-grown ponderosa pine seedlings with controlled-release fertilizer incorporated in the root plug

Abstract

Prior to sowing seeds, three controlled-release fertilizers (fast release (FR), moderate release (MR) and slow release (SR)) were incorporated into the growing media at rates of 0.8, 1.6 or 3.2 g as supplements to nursery supplied soluble fertilizer to grow containerized ponderosa pine (Pinus ponderosa Doug. ex Laws) seedlings in the greenhouse. At lifting, the stem diameter, height and total mass of fertilized seedlings ranged from 14 to 29%, 15 to 22%, and 39 to 100% larger than those of the unfertilized seedlings, respectively. FR provided more balanced nutrients than did MR or SR. The root growth potentials of ponderosa pine treated with 3.2 g of MR or SR were much lower than those of other treatments, indicating that a 3.2 g rate of MR or SR was too high for the seedlings. The estimated best dosages for maximum caliper and height growth were 0.8, 2.2 and 2.0 g for FR, MR and SR fertilizers, respectively.