IntensIve sIlvIculture - Forest Science Labs - Research Network ...

treatments. Soil water loss in treatments where either soil surface evaporation was controlled by
mulching, or where competing vegetation was controlled, was significantly less than water loss
from the shaded and control treatments. Soil water loss in treatments with vegetation controlled
by herbicide was significantly less than in treatments with vegetation controlled by scalping.
Seedlings showed greatest growth with treatments that elicited the most efficient use of available
microsite water either by reducing soil surface evaporation or vegetation competition.
204. Folk, R.S., S.C. Grossnickle, P. Axelrood and D. Trotter. 1999. Seed lot, nursery, and bud
dormancy effects on root electrolyte leakage of Douglas-fir (Pseudotsuga menziesii) seedlings.
Canadian-Journal-of-Forest-Research 29(8): 1269-1281.
Keywords: nursery operations
tree physiology
tree/stand health
photosynthesis
growth
tree phenology
Abstract: The effects of seed lot, nursery culture, and seedling bud dormancy status on root
electrolyte leakage (REL) of Douglas-fir (Pseudotsuga menziesii) seedlings were assessed to
determine if these factors should be considered when interpreting REL for seedling quality. The
relationships of REL to survival, net photosynthesis (Pn), stomatal conductance (gwv) mid-day
shoot water potential ( Psi mid), root growth capacity (RGC), and relative height growth were
determined for each factor in experiments in 1994-95 in nurseries in British Columbia. Nursery
culture had no effect on the relationship between REL and all other measured attributes. Seed lot
affected the relationship between REL and Pn, Psi mid, and survival. However, critical REL (i.e.,
lowest value associated with detectable root damage) and PS80 REL (i.e., level associated with
an 80% probability for survival) were similar between seed lots. Bud dormancy status affected
the relationship between REL and survival, RGC, and relative height growth. Control levels of
REL, critical REL, and PS80 REL decreased as the number of days required for 50% terminal
bud break declined. Thus, terminal bud dormancy status must be known before REL can be used
to assess seedling quality. If the bud dormancy status of Douglas-fir populations is known, then
critical and PS80 REL levels may be useful as indices of root damage.
205. Fox, T.R. 2004. Nitrogen mineralization following fertilization of Douglas-fir forests with urea in
Western Washington. Soil-Science-Society-of-America-Journal 68(5): 1720-1728.
Keywords: fertilization
soil properties
Abstract: Nitrogen mineralization following repeated applications of urea fertilizer was
determined in the A horizon soil from two stands of Douglas-fir [Pseudotsuga menziesii (Mirb.)
Franco] in the Cascade Mountains of Washington. Repeated applications of urea at rates ranging
from 0 to 600 kg N ha-1 were made at annual and 5-yr intervals over a 6-yr period. Nitrogen
fertilization increased N mineralization potential in these soils. However, soil N mineralization
followed a quadratic relationship with the total amount of N applied in fertilizer over the 6-yr
treatment period, increasing up to total application rates of 450 kg N ha-1 and then declining at
higher rates. The decrease in N mineralization rates at the high N fertilization rates may be due to
changes in the quality of soil organic matter, which reduced the effectiveness of extracellular
enzymes and decreases the rate of decomposition and mineralization. Soil pH dropped following
urea fertilization, with greater declines observed in the highest rates of urea fertilizer. Decreases
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