The Effect of Nitrogen Release Technologies and Total Nitrogen on Color and Quality of Kentucky Bluegrass.

Nitrogen recommendations to homeowners are often given as standard pounds of nitrogen per 1000ft² with little to no regard to the nitrogen source.  This project examines various sources of nitrogen with multiple levels of total nitrogen applied over a growing season.  The objective of this project was to maximize turfgrass color and quality while minimizing the total nitrogen applied for the growing season. The research was conducted using Kentucky bluegrass (Poa pratensis).  A randomized complete block design arranged in a 7 x 4 factorial with three replications was utilized with six additional control plots.  The first factor was fertilizer release rates:  1) 18% slowly available (30-0-10), 2) 17% slowly available (30-0-0), 3) 15% slowly available (30-0-6), 4) 11.25% slowly available (25-0-6), 5) 9% slowly available  (32-0-4) 6) 8% slowly available (9-0-0),and 7) 0% slowly available (45-0-0). Nitrogen fertilizers were selected to maximize variation in source and solubility. The second factor was rate of nitrogen.  Plots received either 49kg ha^-1, 98kg ha^-1, 146kg ha^-1 or 195kg ha^-1 nitrogen over a growing season.  Potassium levels were standardized for each fertilizer with appropriate applications of muriate of potash. Plots receiving higher rates of nitrogen performed better overall for turfgrass color and quality. The 8% and 18% slowly available treatments consistently had the lowest color and quality ratings over the spring season regardless of rate applied. Summer color ratings plateaued at 146kg ha-¹ with the exception of the 15% slowly available treatment, which continued to show improvement at the 195kg ha^-1 level. Plots receiving 49kg ha^-1 or less nitrogen ranked below acceptable for fall color and quality on a visual 1-9 scale, with the only exception being the 8% slowly available treatment, which was above the acceptable level at the 49kg ha^-1 treatments.