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The Effect of Nitrogen Fertilization on the Concentration and Weight of Nitrogen, Phosphorus, and Potassium in Douglas-Fir Trees¹

ABSTRACT

Analyses were made of composite samples of needles, live branches, dead branches, bark and wood of 70 Douglas-fir trees taken from five areas and ranging in age from 30 to 50 years. The fertilized trees were from plots that had been fertilized at rates of 200, 300, 500 and 660 pounds of elemental nitrogen per acre.

The data show increased concentration of nitrogen and decreased concentration of phosphorus and potassium in the foliage, as a result of nitrogen fertilization. The nitrogen concentration of other components was also increased, but the concentration of phosphorus and potassium in these tissues did not demonstrate dilution effects that were observed in the needles. The nitrogen:phosphorus ratio in the foliage showed promise for use in diagnosis of nitrogen deficiency of Douglas-fir by foliar analysis.

The data on total weight of nutrients in the trees on an area basis show that almost twice as much nitrogen, greater quantities of potassium and approximately equal amounts of phosphorus were contained in the vegetation on certain fertilized plots as were contained in the unfertilized vegetation. Needles showed the greatest increase in nitrogen, with branches and bark showing lesser increases, and wood no increase.

¹ Contribution from the College of Forestry, University of Washington, Seattle. This material has been presented by the senior author as a portion of a thesis in partial fulfillment of the Ph.D. degree, University of Washington. The project was supported by funds provided by Initiative 171. Presented before Div. V-A, Soil Science Society of America, Nov. 29, 1961, at St. Louis, Mo.

² Instructor, Skagit Valley College, Mount Vernon, Wash., formerly Research Associate, University of Washington.

³ Professor of Forest Soils, College of Forestry, University of Washington.

Received for publication February 23, 1962. Accepted for publication March 6, 1962.