Wednesday, November 15, 2006 - 11:00 AM
282-8
Dissolved Organic Nitrogen Dominates Extractable Nitrogen Pools in Cranberry bBds.
Documenting processes and patterns of plant available nitrogen throughout the growing season will provide a mechanistic approach to understanding nitrogen cycling in cranberry beds. Nitrogen inputs to the cranberry agroecosystem are carefully managed by growers, since too much nitrogen causes excess growth at the expense of yield. Ammonium is the preferred nitrogen source for cranberries, and fertilizer applications rates range from (20-60 kg/ha/yr). Organic forms of nitrogen, such as amino acids or tannin bound proteins, may also be used by the plant. In Central Wisconsin, between 40 – 60% of cranberry roots are infected with an ericoid mycorrhizal fungus. These fungi can access dissolved organic forms of nitrogen, that otherwise may be unavailable to the plant. Preliminary data from five cranberry beds indicate that the total extractable nitrogen pool is low, ranging between 5 – 15 kg/ha. Organic nitrogen is the largest component with lower amounts of ammonium and nitrate. When plants are actively growing, during June and July, dissolved organic nitrogen remains the primary form of extractable nitrogen, but inorganic nitrogen is available only in trace amounts. Given the presence of organic nitrogen in soil nitrogen pools and relatively steady colonization rates, dissolved organic as well as inorganic nitrogen may comprise an important component of nutrient cycling in cranberry beds. Decomposition and mineralization rates will also affect extractable nitrogen pools. These may vary across beds depending on litter quality, soil moisture content, temperature, and pH. Therefore combining measurements of pools as well as fluxes in a cranberry agroecosystem will provide a more complete picture of nitrogen cycling in cranberry beds.
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