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Height Growth Response of Douglas Fir to Nitrogen Fertilization¹

ABSTRACT

This paper presents the results of initial nitrogen fertilization trials on 15 to 20-year old natural Douglas fir stands growing on poor sites (Site Class IV, V) in western Washington. Annual height growth was used as the criterion of response. On both shallow residual and deep glacial outwash soils response to nitrogen was very marked. Larger more vigorous trees responded more than smaller trees and resulted in more rapid suppression of these small trees. Foliage color changed from yellow to dark green after fertilization and before height growth response. Nitrogen content of needles increased from less than 1% to 1.2 to 1.8% after fertilization. Some aspects of fertilization of forest lands are discussed including use of fertilizers for Christmas tree production.

¹ Financial support for this work was received from funds supplied through Washington State Initiative 171. Revision of a paper presented before Div. V-A—Soil Science Society of America, Dallas, Texas, Nov. 20, 1953.

² College of Forestry and Department of Botany, respectively. University of Washington, Seattle.

Received for publication February 11, 1954.