EFFECTS OF BASE CATION FERTILIZATION ON SOIL AND FOLIAGE NUTRIENT CONCENTRATIONS, AND LITTER-FALL AND THROUGHFALL NUTRIENT FLUXES IN A SUGAR MAPLE FOREST

Application of base cation fertilizers is widely used to ameliorate de cline symptoms in hardwood forests in southern Quebec, but little is k nown about the effects of fertilization on nutrient cycling. Control a nd fertilized plots in a sugar maple (Acer saccharum Marsh.) dominated stand were monitored over a 4-year period to determine the effects of fertilization on exchangeable soil base cations in soil, foliar nutri ent concentrations, and fluxes of N, K, Ca, and Mg in litter fall and throughfall. Fertilization had a large, immediate effect on exchangeab le K, whereas effects on Ca and Mg were delayed and restricted to the organic forest floor, presumably because of the lower solubility of th e limestone-based Ca and Mg components of the fertilizer. Fertilizatio n raised pH in the organic forest floor the second and third years aft er application but had no effect in the B horizon. Foliar K, Ca, and M g were elevated in the year of fertilization, but foliar concentration s of Ca and Mg did not differ from, or were lower than, controls in fo llowing years. Litter-fall K flux was increased by fertilization, but litter-fall Ca and Mg fluxes and all throughfall base cation fluxes we re unaffected. In control plots, nutrient concentrations in soil remai ned relatively constant throughout the study, but foliar concentration s and, in particular, litter-fall fluxes varied widely from year to ye ar. This natural variation caused control plots to shift from a state of deficiency in N, Ca, and Mg to a nutrient-sufficient state between the first and second years of study. Fertilization effects are superim posed on a naturally variable nutrient cycling system, and controls on this variability must be understood if fertilizer response is to be a ccurately predicted.