Agronomic and physiological responses of cool-season turfgrass to fall-applied nitrogen

Turfgrass is an integral component of the urban and suburban landscape and plays a key role in water quality and nutrient cycling. Nitrogen (N) is the mineral nutrient most limiting for turfgrass growth and development and is often applied as fertilizer to maintain adequate soil levels. Rising energy and subsequent N costs and environmental concerns have pressured turfgrass managers to schedule N applications to maximize N use efficiency. Late-fall N fertilization for cool-season turfgrass is a widely accepted practice among turf managers, with application rates ranging from 49 to 98 kg N ha^-1 and accounting for 25 to 50% of annual N applied. Reported benefits from late-fall N fertilization include improved color in fall and spring without stimulation of shoot growth, improved rooting in late fall and early spring, carbohydrate accumulation in late fall, and the ability to delay or avoid fertilizing in the spring. However, research supporting these benefits in cool-season turfgrass is limited and has yielded mixed results. Much of this work was conducted in relatively warm or temperate coastal climates and may not be applicable to cooler temperature regimes of more northern climates. More recent research has indicated a greater potential for nitrate leaching losses from late-fall N due to cooler temperatures reducing plant uptake and microbial immobilization of N. This literature review finds that the often cited physiological and agronomic benefits of applying late-fall N applications are poorly supported by peer-reviewed research, with the exception of fall and spring color responses. More climate-specific research on plant utilization and response to fall-applied N is necessary to determine appropriate N rates and optimal timings for this highly specific application.