Nitrogen Source and Rate Effects on Velvet Bentgrass Putting Greens.

Nitrogen source and rate effects on velvet bentgrass (Agrostis canina L.) are not well documented, particularly in the midwest portion of the USA.  Claims have been made, stating that on velvet bentgrass, fertilizers with greater acidifying effects work better than urea or nitrate fertilizers.  Claims about N sources seem to be based mostly on anecdotal evidence.  This study was conducted to determine if urea, calcium nitrate, and ammonium nitrate applied as liquids are suitable for use on velvet bentgrass putting greens and to compare them to the more acidifying ammonium sulfate.  A second objective was to determine how N application rates (49, 146, 244 kg ha^-1 yr^-1) affect agronomic and playability characteristics of velvet bentgrass for each N source.  The study was conducted using ‘Vesper’ velvet bentgrass and was replicated on two soil types in Verona, WI.  The two soil types included an 80:20 sand:peat mixture and a Troxel silt loam.   Fertilizer applications were made every two weeks during the growing season months from June 2007 through October 2008.  Data from the 2007 growing season suggested that when velvet bentgrass is grown on sand, fertilizing with urea and ammonium nitrate provides better turf quality and higher relative chlorophyll contents over time.  On soil, N type had no effect on turf quality or relative chlorophyll content.  Fertilizing velvet bentgrass grown on soil with 49 kg N ha^-1 yr^-1 resulted in average quality ratings of around 5.5.  On sand, average quality ratings of 5.5 were not observed until 244 kg N ha^-1 yr^-1 was applied.  Results from 2007 suggest that urea and ammonium nitrate are acceptable N sources for velvet bentgrass grown on sand.