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Response of 30-Year-Old Douglas-Fir to Fertilization¹

ABSTRACT

This paper presents the 5-year growth increment of a 30-year-old Douglas-fir stand after fertilization. Nitrogen was applied initially at the rate of 100 pounds per acre. Subsequent yearly additions have brought the total to 350 pounds. Soil nitrogen content before fertilization was 0.12% and Douglas-fir site class was a high V with a stocking of 3,500 trees per acre. Small quantities of phosphorus, potassium and lime were applied initially only.

The fertilizer treatment has resulted in the following growth modifications:

1. Accelerated diameter growth, particularly in the larger diameter classes.
   
2. Accelerated volume growth on both a tree and a stand basis. The fertilized stand had approached Site III in periodic annual increment.
   
3. Development of natural competition and more rapid suppression of small trees on the plot.
   
4. Fifty largest trees on the fertilized plot produced about the same periodic annual increment as the total stand on the unfertilized plot.
   

¹ Funds for this project were supplied from Washington State Initiative 171. The writers wish to acknowledge the assistance of Harry Anderson, graduate student at the College of Forestry. Presented before Div. V-A, Soil Science Society of America, Davis, Calif., Aug. 17, 1955.

² Assistant Professor and graduate student, College of Forestry, University of Washington, Seattle.

Received for publication February 2, 1956. Accepted for publication November 9, 1956.