Cool-Season Lawn Turf Response to Fall Applied Nitrogen Programs in the North Central States.

Lawns are fertilized with nitrogen (N) to sustain green color, promote shoot density and plant vigor. To maximize N-fertilizer benefits without growth surges and encourage carbohydrate storage, turf scientists have historically recommended that N be applied to cool-season grasses primarily during the autumn months. Recently, several states have passed laws that limit the ability to apply N-fertilizer in late autumn. This has prompted scientists to reevaluate the dogma regarding N fertilizer application timing for these species. This multi-state field study evaluated the effects of four autumn N-fertilizer programs, 98 kg N ha^-1 yr^-1, using a widely available granular homeowner fertilizer product. Programs varied by application timing: 49 kg N ha^-1 in late-summer (LSUM) plus an additional 49 kg N ha^-1 in Sept., Oct. or November. These programs were compared to an unfertilized control and a 49 kg N ha^-1 spring only application. Turf N response was primarily quantified by measuring canopy color with hand-held reflectance devices. The general results indicated that the LSUM + either a Sept. or Oct. application provided the most sustained green color response. Although some greening occurred at some sites from the Nov. application, substantial color benefits were delayed until the following spring. These results continue to help turf scientists refine recommendations for optimum lawn N fertilizer application timings.