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Nutrition and fertilization response : a case study using hybrid poplar Zabek, Lisa M.

Abstract

Three hybrid poplar (Populus trichocarpa x Populus deltoides) plantations on the east side of Vancouver Island were fertilized with N, Nand P, and N, P, and K at the beginning of the third growing season, followed by fertilization with N in the fourth growing season. Three-yearvolume growth increased with application of N alone, but was greatest in plots receiving both N and P. Potassium added with the N and P provided a slight benefit at one site. Litterfall biomass and leaf area of one clone increased with fertilization and remained unchanged in a second clone, as compared with untreated controls. Foliar N and P concentrations were linearly correlated with leaf area index, and leaf area index was linearly correlated with poplar volume growth. Amounts of N and P resorbed from the foliage increased with fertilization, but resorption efficiency and proficiency were unaffected by fertilization. Foliar resorption efficiency and proficiency of N and P differed between two of the three sites. Diagnostic techniques tested to determine if poplar growth response to fertilization could accurately be predicted were soil analysis, critical foliar nutrient concentrations, foliar N:P ratios, Diagnosis and Recommendation Integrated System (DRIS) analysis, optimum nutrient ratios and vector analysis. Neither soil chemical characteristics nor DRIS analysis were an effective diagnostic tool. Fertilizer prescriptions including the nutrients diagnosed as limiting using critical foliar nutrient concentrations, matched tree growth response to fertilization 63% of the time. A foliar N:P ratio of 9.5 coincided with differences in tree growth response to N or N-plus- P application. In a nursery trial, steady-state nutrient ratios were derived for three hybrid poplar clones. Ratios were somewhat similar among clones, but were not identical. Fertilizer prescriptions derived from differences between the diagnostic ratios and foliar nutrient ratios of unfertilized trees in the field had a success rate of 63%. Diagnoses of nutrient limitations from vector analysis using the whole plant, shoot, foliage and root tissues of poplar growing in the nursery were dissimilar among tissues. Foliar vector analysis provided the best index of tree growth response to fertilization.

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