Biomass and Soil Nitrogen Relationships of a One-Year-Old Sycamore Plantation
1991
Tschaplinski, T. J. | Norby, R. J. | Todd, D. E. | Johnson, D. W.
Maximum efficiency in biomass production in short-rotation woody crops requires a level of N fertilization that achieves a balance between maximum growth and minimum NO⁻₃ leaching into groundwater. The effects of urea-N fertilizer applied under various timing regimes were investigated in a plantation of American sycamore (Platanus occidentalis L.), and different aspects of optimum fertilization were explored. A plantation of sycamore was established at Oak Ridge, TN, typically a N-poor area. Nitrogen treatments consisted of differing schedules of urea application, including trees fertilized at the beginning of the growing season with 0, 50, 150, and 450 kg N/ha, and trees fertilized periodically (three times during the growing season) at 37.5 kg N/ha. Fertilization effects on stem and leaf biomass, leaf nutrient concentration, soil N characteristics, including available N, mineralizable N, nitrification potential, and NO⁻₃ leaching loss were determined. The greatest aboveground biomass accumulation (three times greater than that of unfertilized controls) was obtained with 450 kg N/ha, but with greater NO⁻₃ leaching. Nearly as much biomass was obtained with almost no NO⁻₃ leaching when much less N was added either early in the season (150 kg N/ha) or in periodic applications (37.5 kg N/ha three times). The rapid decline to control levels of soil available N in all treatments, and the results of the aerobic incubations, indicate high nitrification potential at the site. The results suggest that periodic, low N fertilization may be optimal on sites with a high nitrification potential, and that the lower rates tested minimize NO⁻₃ contamination of groundwater.
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