Predicting 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 will set up a series of 15-25 year-old Douglas-fir plantations to study fertilizer response. The study will be set up as a paired tree study where tree matching characteristics include DBH and crown height. One tree from each pair will be randomly selected to receive nitrogen fertilization at 227 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, bulk density, etc). Equipment will be used to measure rainfall, temperature, and soil moisture over a long-term period. Tree growth characteristics and foliage nutrition will be measured two years after fertilization, while soil nutrition will be measured four years after fertilization. This study will determine if site properties, environmental factors, and/or nutrition can predict N fertilizer response in Douglas-fir.