Monday, November 5, 2007 - 11:00 AM
76-6
Is Leaf Nitrogen in Stockpiled Tall Fescue Used for Root Growth During Winter?.
During winter months, leaf concentrations of nitrogen (N) and other phloem mobile macronutrients decline in tall fescue (Festuca arundinacea). The decline has not been attributed to the remobilization to other plant tissues or to leaching of aboveground biomass. The objectives of this field study were to determine (a) if N in stockpiled tall fescue leaves is remobilized during the winter months and, if so, (b) which tissues utilize the remobilized N. An established tall fescue pasture in central Missouri was selected and plants were confined using 25cm diameter PVC pipe driven into the ground to a 20cm depth. In autumn, 14NH415NO3 was applied to all exposed leaf surfaces. Above and belowground tissues were harvested monthly throughout the winter and early spring and the 15N label was used to monitor leaf N mobilization to other plant structures throughout this period. Surface soil samples of the top 1cm were collected monthly. Atom%15N of the separated tissues and soil samples were determined by continuous flow isotope ratio mass spectrometry. 15N-enrichment occurred in all tissues throughout the 2005-2006 winter months. Excluding the 15N-treated leaf tissue, tillers that had formed after 15N application contained the majority of the label. In April, new tillers contained about 15% of the applied 15N while the rhizomatous bases of these tillers contained up to 3.5%. The fine root system of tall fescue proliferated in mid-winter and contained up to 2% of the applied 15N. Contamination from washing or leaching of the 15N label was not found in the soil samples. These results suggest leaf N is remobilized to underground structures and is utilized for both new root and shoot growth in late winter and early spring. Results of current analyses for the 2006-2007 winter will be discussed as well as possible N pools affected in each tissue.
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