Response of Creeping Bentgrass to Fall-Applied Nitrogen On Sand and Soil Putting Greens in the Upper Midwest.

In temperate climates, late season nitrogen fertilization of turfgrass is widely considered to be the most important nutrient management practice of the year. In Wisconsin, golf course superintendents apply late season nitrogen between September and December with rates ranging from 25 to 200 kg ha-1. While the benefits of late season nitrogen fertilization have been evaluated by past researchers, uncertainty remains regarding ideal rates and timings as influenced by climate, soil type, and turfgrass species for the North Central US. The objective of this research was to identify the optimal rate and timing for late season nitrogen fertilization for sand and mineral soil creeping bentgrass putting greens in the North Central US. Field studies were conducted in Madison, WI and St. Paul, MN; 'L93' creeping bentgrass (Agrostis stolonifera L.) was grown separately on mineral soil and sand root zones on each site. A completely randomized design on each soil type at each location compared three nitrogen application rates and three application timings with three replications. Nitrogen rates were applied at 0, 25, and 49 kg ha-1 with applications made on the 15th of September, October, or November 2008. Weekly chlorophyll index, turf quality ratings, and clippings were collected in 2008 and 2009. September applications at both sites resulted in a coincident greening and growth surge proportional to application rate. October applications at both sites resulted in a greening, but no extra growth compared to the unfertilized control. This response was similar for 25 and 49 kg ha-1 rates. No fall color or clipping responses were observed for the November applications. In early spring 2009, October and November treatments had the greatest chlorophyll index and November treatments had the highest growth rate. No significant differences in color or growth were observed in the spring between the unfertilized and September treatments.