Western Hemlock and Douglas-Fir Seedling Development with Exponential Rates of Nutrient Addition

Abstract

Abstract Ingestad's concept of controlling relative addition rate was used in growing western hemlock (Tsuga heterphylla [Raf.] Sarg.) and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings in styroblock containers under greenhouse conditions. Seedlings were fertilized for 14 weeks at different exponential rates following a 1 month pretreatment period. Based on their initial nitrogen contents, seedlings were fertilized with a complete Ingestad solution, twice weekly, at either a 1, 2, 4, or 6% per day exponentially increasing dosage, or with a constant amount each feeding (control treatment) of 0.991 mg N/seedling. Western hemlock and Douglas-fir seedlings grew fastest at the highest (6%) relative addition rate. Douglas-fir was more efficient than western hemlock at nitrogen uptake and succeeded in taking up the most nitrogen (55% of the nitrogen added) in the control treatment. Western hemlock was most efficient at nitrogen uptake in the 4% relative addition rate treatment, but still captured only 29.7% of the nitrogen added. Biomass allocation and nitrogen concentrations in seedlings of both species varied significantly with treatment, suggesting that different seedling types acclimated to different levels of nutrient stress could be produced using the concept of relative addition rate. The nitrogen concentrations of seedlings generally declined with time in the control and lowest relative addition rate treatments. For. Sci. 37(1):54-67.