Fall Fertilization with N and K: Effects on Douglas-Fir Seedling Quality and Performance

Abstract

Abstract Coastal Douglas-fir (Pseudotsuga menziesii) 1+1 seedlings were fertilized with two fertilizers [NH4NO3+K2SO4 and (NH4)2SO4+KCl] at four rates (0, 80, 160, 320 kg N and K/ha) split over three application dates (September 19, October 13, November 1, 1996). Fertilizer type did not affect total Kjeldahl nitrogen (TKN) levels on any of the sampling dates. By January 10, TKN concentrations had increased 16, 30, and 34%, and chloride concentrations had increased 57, 77, and 112% relative to the unfertilized seedlings for the 80, 160, and 320 kg N+K/ha treatments, respectively. Nitrate levels increased briefly after the first application of NH4NO3+K2SO4. Potassium levels remained relatively unchanged. Levels of most other nutrients, as well as foliar dry weight, increased between September 16 and January 10, but these increases were generally unrelated to the fertilizer treatments. Root growth potential and cold hardiness did not differ among treatments. Seedlings that received 160 or 320 kg N/ha broke bud an average of 3 days earlier than did the unfertilized seedlings. Chlorophyll fluorescence (Fv/Fm) of fertilized seedlings was consistently higher than that of unfertilized seedlings on November 13 and December 30. These treatment differences were not reflected in seedling outplanting performance after one growing season. West. J. Appl. For. 16(2):71–79.