Color and Growth of Douglas-Fir Christmas Trees as Affected by Fertilizer Application
1966
Turner, Darrell O.
Eight fertilizer treatments of varying amounts of N, P, K, S, and Mg were applied to a chlorotic stand of 15-year-old Douglasfir (Pseudotsuga menziesii) Christmas trees grown upon glacial moraine soil in the Puget Sound basin. Color ratings, growth measurements, and foliar analyses data were collected during two growing seasons. Fertilizer N rates from 0.125 to 1.0 lb/tree improved color the first season without influencing growth. All rates of N improved color the second season, but only the 0.125 N level produced an acceptable rate of growth. Rates of N above 0.125 lb/tree overstimu'ated growth for Christmas tree production. Color was correlated to total-N levels in the foliage; trees with dark green foliage had high total-N contents. Treatment with P and K in the absence of N did not improve color or increase growth. Treatment with N, P, K, S, and Mg gave the darkest green color and highest total-N level the first year, but color faded and total-N content declined in the second season. Cones were formed only on trees which received the N-P-K and N-P-K-S-Mg treatments.
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