Variance in response of pole-size trees and seedlings of Douglas-fir and western hemlock to nitrogen and phosphorus fertilizers.

Abstract

Three experiments were conducted to determine effects of N and P fertilizers on growth and levels of plant-tissue nutrients of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western hemlock (Tsuga heterophylla (Raf.) Sarg.). Both pole-size trees in closed-canopy stands and potted seedlings were use d . Soil series were Bunker for Douglas-fir and Klone for western hemlock in experiments 1 and 3, and Vesta in experiment 2. For each species in experiments 1 and 2, P and N fertilizers were tested in six or eight treatments using factorial design. In experiment 3, N and P fertilizers were individually tested on seedlings, at one rate of application each. Nitrogen fertilizers used were urea in experiment l and ammonium nitrate in the other two experiments; P was applied as triple superphosphate in all three experiments. In general, fertilization changed levels of some plant-tissue nutrients of the pole size trees and potted seedlings. Neither height nor basal-area growth of the trees was significantly affected by any of the fertilization treatments in the first two experiments. Seedling growth of both Douglas-fir and western hemlock was dramatically improved by the P fertilizer, but was negatively affected by the N fertilizer. Results clearly show differences between pole-size trees and seedlings in response to N and P fertilizers. They also suggest that N not be applied where soils are high in N and low in P and that P applications be confined to sites with low-P soils, when trees are young, before canopy closure.

Citation

Radwan, M.A.; Shumway, J.S.; Debell, D.S.; Kraft, J.M. 1991. Variance in response of pole-size trees and seedlings of Douglas-fir and western hemlock to nitrogen and phosphorus fertilizers. Canadian Journal of Forest Research. 21: 1431-1438.