Foliar and Granular Nitrogen for Creeping Bentgrass.

Creeping bentgrass (A. stolonifera) has long been used in the transition zone of the United States as a putting green surface.  However, summer heat and humidity will thin turf and reduce root growth, and so many golf course superintendents include foliar N fertilization in their maintenance regime as a means to supply N to stressed turf.  However, information regarding N timing and N rates is lacking, especially in the humid southeast US.  The objective of this work was to examine combined and separate effects of foliar N rate and timing of irrigation on the color, quality, shoot density, root growth, and percent N content of ‘Penn A-4’ creeping bentgrass.  Conducted over 2 years, the experiment consisted of 4 N rates (0.5, 1.0, 2.0, and 4.0 g m^-2) and 3 N application methods (Granular – watered after application, Foliar – watered after application, and Foliar – no water after application), all replicated 4 times on a ‘Penn A-4’ putting green.  Collected data included weekly color and quality, clipping yield and N content at 1 and 3 weeks after application, quarterly shoot and root density, and twice-yearly carbohydrate content.  The highest N rate was needed to achieve maximum color and quality ratings, except in the summer, when application of foliar N (without a following irrigation) reduced turf quality via foliar burn.  For best turf color and quality (especially when granular sources were used) the monthly rate of 4.0 g m^-2 would likely maintain constant N levels within the plant and consistent turf color if applied twice throughout the month at 2.0 g m^-2.