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UBC Theses and Dissertations

Effects of repeated fertilization and a straw application to the organic layers under Jack Pine and seedling response Kumi, Janna W.


In an optimum nutrition experiment, a 45-year old jack pine (Pinus banksiana Lamb.) stand in Quebec was repeatedly fertilized over a 10-year period with various levels of NPK fertilizers. In a separate experiment, a straw treatment was applied over snow to smother the ericaceous ground vegetation. Nitrogen fertilizer additions for 10 years resulted in increased humus biomass in all treatments. The greatest gain was on plots receiving repeated low N doses. These organic layers also had the lowest decomposition rates. Heavier N applications increased humus decomposition substantially, but stand litter production was also increased. The straw-treated humus had decomposition rates approaching those found with high N additions. Repeated low N additions immobilized fertilizer N within the humus. Most of the N applied at higher treatment levels appears to have been lost. Nitrogen mineralization rates were investigated in an aerobic incubation study. Nitrification occurred in spite of low pH (<4) on high N plots. The straw addition increased humus nitrogen mineralization rates. The results of repeated additions of P and K were variable. Additions of P and K decreased nitrogen availability although decomposition rates were increased. It appeared that most of the P and K were lost from the organic layers due to leaching. Large N additions had little effect on the humus C/N ratio. They increased the CEC and the pH but reduced the base saturation. Straw additions lowered the humus C/N ratio but increased the CEC, pH and base saturation. Dramatic changes in the ground vegetation occurred. With higher N additions the ericaceous vegetation was greatly reduced and increasingly replaced with Sambucus, Aster and other exotics. The straw application effectively smothered the ericaceous vegetation for 10 years. Seedling bioassay studies showed that both the straw treated humus and the sustained low additions of N plus P and K resulted in the highest seedling biomass. This correlated well with stand growth response. Seedling N nutrition was adequate in all treatments and reflected the ability of mor humus to release immobilized N under improved environmental conditions in the greenhouse. Some possibilities why foliar N could not be correlated with seedling biomass are discussed. It is concluded that in jack pine stands with thin mor humus layers, repeated light nitrogen additions plus phosphorus and potassium result in sufficient nutrient turnover rates to ensure the highest stand response.

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