Nitrogen Allocation of Late Fall Applications in Creeping Bentgrass and Poa Annua.

A ‘Penncross’ creeping bentgrass and Poa annua turf mowed at golf course fairway height were treated with ¹⁵N double-labeled urea (10 atom % excess) in solution at 49 kg N/ha on Nov. 11, 2010 to determine nitrogen allocation in turfgrass and soil from late fall fertilizer applications.  Soil and turf samples were extracted with a 10 cm diameter cup cutter to a depth of 8 cm, 7 and 14 days after treatment (DAT) and then the following spring on March 15 and April 15, 2011. Three untreated samples were collected outside the treatment area as an untreated control. Verdure, which includes any aboveground tissue and crowns, was separated from the thatch and soil. The thatch was separated from the soil and roots were separated from the soil for analysis.  Turf and soil components were dried in a convection oven for 72 h at 60°C.  Samples were weighed and prepared for ¹⁵N enrichment analysis by a mass spectrometer.  All samples from the 2010-2011 winter period were processed and submitted for mass spectrometer analysis.  Complete date analysis and interpretation is currently being finalized.  The 2011 treatment application was made on Nov. 8.  Soil and turf samples were collected at 7 and 14 DAT, and in March and April 2012. Following spring sample collection and processing, samples will be submitted for mass spectrometer analysis, data analyzed, and results finalized.