Late Fall Fertilization of Kentucky Bluegrass

Many turfgrass managers apply a portion of the total yearly N to cool-season turfgrasses in the late fall (November). The purpose of this field study was to compare fertilization programs with and without N applications in November using both slow-release and soluble N sources. Turfs of two different cultivars of Kentucky bluegrass (Poa pratensis L. cv. Baron and cv. Newport) growing on a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) received 10 fertilization programs utilizing urea, isobutylidene diurea (IBDU), or sulfur-coated urea (SCU). Urea was applied four times per year with either a spring application or a late-fall application combined with applications in early June, mid-July, and early September (171–196 kg N ha–1 yr–1). For IBDU and SCU, application dates and N rates (kg ha–1) consisted of June 98 + September 98, June 98 + November 98, and June 49 + September 49 + November 74. The turfs were rated for color for 3 yr, and clipping weights were determined weekly for the final 2 yr of the study. Results were generally similar for both cultivars, except fewer significant differences in spring color ratings were found on Newport. An application of urea in November, without a subsequent spring fertilization, resulted in higher turf color ratings in the early spring but lower turf color ratings in May and June, compared to turf receiving a spring fertilization. Results indicate that a late-fall application of urea may not eliminate the need for spring fertilization but may allow a reduction in the amount of N applied in spring. Turfs fertilized with SCU in November received higher color ratings in the spring than did turf fertilized with SCU in September. With IBDU, the June + September program resulted in the highest number of ratings with acceptable turf color. November IBDU applications did not result in higher color ratings in the spring and resulted in inefficient use of the N applied