Graduate Thesis Or Dissertation
 

Fall fertilization effects on Douglas-fir seedling quality

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  • Coastal Douglas-fir (Psuedotsuga menziesii (Mirb.) Franco) 1 + 1 seedlings were fertilized with two types of fertilizers (NB4NO3+K2SO4 and (NH.4)2 SO4+KC1) at four rates (0, 80, 160, 320 kg N and K/ha) split over 3 application dates (September 19, October 13, November 1, 1996). By January 10, total Kjeldahl nitrogen (TKN) concentrations increased 16, 30, and 34% and contents increased 6, 20, and 26% for the 80, 160, and 320 kg N/ha treatments relative to the unfertilized seedlings. Potassium levels remained relatively unchanged as a result of the fertilization treatments. Chloride concentrations increased 57, 77, and 112% and contents increased 45, 71, and 92% for the 80, 160, 320 kg K/ha as KC1 relative to the unfertilized seedlings. There was an immediate pulse in nitrate levels following the first application of NH4NO3+K2 SO4, but this was of short duration. Levels of most other nutrients continued to increase between September 16 and January 10, but these increases were generally unrelated to the fertilizer treatments. Although TKN levels increased, nutrient ratios determined as a proportion of TKN decreased, but generally remained within balance. Needle dry weights also increased at this time, but the increase was not related to the treatments applied. There were no differences in root growth potential (as measured by total new root dry weiglht) among the treatments. Seedlings that received 160 and 320 kg N/ha broke bud three days earlier than the unfertilized seedlings. Seedling cold hardiness LT50 levels on October 23, November 13, and December 9 showed no consistent significant differences among the fertilizer treatments. By December 30 all treatments had attained similar LT50 levels (-14°C). Adding high levels of fertilizers after budset in the fall did not appear to disrupt the cold hardiness process. Detectable differences in baseline seedling variable chlorophyll fluorescence Fvar/Fmax levels among the treatments occurred on November 13 and December 30. Fertilized seedlings had consistently higher Fvar/Fmax than unfertilized seedlings. Fall fertilization to stimulate late season luxury consumption of nitrogen appears to be beneficial if conducted after seedlings have ceased growth and set bud. If no biologically significant nutrient imbalances occur as a result of fertilization, as was the case in this study (up to 320 kg N/ha), seedlings with elevated levels of nitrogen may outperform seedlings with lower levels of nitrogen.
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