Soil and Site Factors That May Predict Nitrogen Fertilizer Response in Douglas-Fir Plantations.

Nitrogen fertilization is common in Pacific Northwest plantation forests, although there is not always a growth response to fertilization.  The Stand Management Cooperative has set up a series of 15-25 year-old Douglas-fir plantations to study fertilizer response.  The study uses paired trees with matching characteristics of DBH and crown height.  One tree from each pair will be randomly selected to receive nitrogen fertilization at 224 kg N/ha.  Sites will be characterized by site properties (site index, LAI, slope, etc), environmental factors (precipitation, soil moisture and temperature, etc), and nutrition (soil and foliar nutrition, parent material, etc).  Equipment will be used to measure rainfall, temperature, and soil moisture over a long-term period.  Tree growth characteristics, foliar nutrition, and soil nutrition will be measured two years after fertilization.  This study will determine if site properties, environmental factors, and/or nutrition can predict nitrogen fertilizer response in Douglas-fir.