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Soil Science Society of America Journal Abstract -

Effects of Different Urea Fertilizers on Soil and Trees in a Young Thinned Stand of Western Hemlock


This article in SSSAJ

  1. Vol. 53 No. 3, p. 941-946
    Received: Feb 25, 1988

    * Corresponding author(s):
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  1. M. A. Radwan  and
  2. D. S. DeBell
  1. Forestry Sciences Lab., Pacific Northwest Res. Stn., USDA Forest Serv., Olympia, WA 98502



Effects of three different urea fertilizers on selected chemical characteristics of soils and foliage, and on growth per tree of a 24-yr-old thinned stand of western hemlock [Tsuga heterophylla (Raf.) Sarg.] were compared at a site in coastal Oregon. Treatments were the following: untreated control (C), urea (U), urea treated with N-Serve®1 [nitrapyrin, 2-chloro-6-(trichloromethyl) pyridine] (U + NS), and sulfur-coated urea (SCU). Fertilizers were uniformly applied by hand to 0.03-ha plots in March at 224 kg N ha−1. Soil, to a depth of 20 cm, and current-year foliage were sampled periodically for 2 yr. Height and diameter of 10 dominant or codominant trees per plot were measured annually for 6 yr. Treatment effects on soil pH varied by fertilizer and sampling date; throughout, pH was lower with U + NS than with U, and the smallest change in pH was associated with SCU. Effects of fertilizer on inorganic N in the soil and on foliar nutrients varied by fertilizer and sampling date. Initially, N-Serve inhibited nitrification and produced the highest NH4-N concentrations. In general, all fertilizers increased inorganic N in the soil and total N in the foliage. Fertilizers significantly reduced foliar concentrations of some other macronutrients, especially in the first year after fertilization; some depressions were significantly less with SCU than with the other two fertilizers. Height growth per tree was not significantly affected by any of the fertilizers. Basal-area and volume growth per tree were significantly greater with the SCU treatment than with the control, U, or U + NS treatments. Beneficial effects of SCU seemed to be mostly due to the slow release of N from the fertilizer, although some positive effect of S cannot be ruled out.

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