Response of kentucky bluegrass turf to fertilizers containing dicyandiamide

Nitrogen fertilization is of major importance in maintaining turfgrass stands. Although rates and sources of N may vary on different turfgrass areas, efficient utilization of N applications is always important. This research was conducted in the field to determine the value of dicyandiamide (DCD) as a nitrification inhibitor and as a slow-release N source in turfgrass fertilization. The inhibitory effect was studied by applying ammonium sulfate (AS), urea, and a complete fertilizer alone and with 10 and/or 15% of the N replaced with DCD-N to stands of Kentucky bluegrass. Single and split rates totaling up to 196 kg N/ha/yr were used. Soil NO₃-N and NH₄-N analyses sometimes indicated decreased nitrification; however, turfgrass yield and color were essentially unaffected by these rates of DCD. To assess the slow-release effect of DCD, various ratios of AS-N or urea-N to DCD-N were used to fertilize turf in two experiments. Initial response decreased as the proportion of DCD-N increased, and in one experiment, a residual effect was noted a year after application when DCD comprised 80 or 100% of the N. Severe, but short-lived, phytotoxicity from DCD was noted in the other experiment when more than 40% of the N was from DCD. Under the conditions of this research, DCD appeared to have little value in increasing the efficiency of N fertilization.