EVALUATION OF NITRIFICATION INHIBITORS AND SLOW RELEASE N SOURCES FOR USE ON TURFGRASSES (DICYANDIAMIDE, OXAMIDE, MELAMINE, KENTUCKY BLUEGRASS)

Field studies were conducted to evaluate the potential of dicyandiamide (DCD), dyrene, duosan, ridomil (metalaxyl), dwell (ethazole), and carbyne (barban) as nitrification inhibitors in turfgrass fertility programs. Dicyandiamide was incorporated into granules of urea and ammonium sulfate so that 10% of the N was derived from DCD, and applied at 196 kg N ha(\u27-1) yr(\u27-1) in two and four applications to Kentucky bluegrass (Poa pratensis L.). Dicyandiamide did inhibit NO(,3) formation 24 days after fall application, but not 38 days after application the previous fall. No effect of DCD on N uptake, turf response or spring inorganic N levels were observed. Dyrene, duosan, ridomil, dwell and carbyne were applied at 2.2 kg ha(\u27-1) a.i. with 196 kg N ha(\u27-1) urea in four applications. These inhibitors did not significantly improve turf quality, N uptake or clipping yields. Late fall applications had little effect on soil inorganic N concentrations in the fall or spring. A field study was conducted to determine the N release characteristics of oxamide in applications to Kentucky bluegrass. Coarse and fine oxamide were applied at a rate of 196 kg N ha(\u27-1) yr(\u27-1) in two and four applications. Coarse oxamide exhibited good slow-release characteristics when applied at two applications of 98 kg N ha(\u27-1). The release of by fine oxamide was faster, but the time period for residual N release was shorter than coarse oxamide. This particle size of oxamide was better suited to four applications of 49 kg N ha(\u27-1) yr(\u27-1). Melamine (2,4,6-triamino-1,3,5-triazine) and ammeline (4,6-diamino-1,3,5-triazine (1H)-al were tested for N release characteristics over a 16 week period. Melamine was also combined with equal amounts of urea-N in a granule and in suspension. One and two applications of 98 kg N ha(\u27-1) were evaluated. The release of N from melamine and ammeline was slow. Soil concentrations of NH(,4) and NO(,3) in the surface 7-cm were less than 5% of the total N applied over a 56 day period. Poor turf quality also reflected the lack of N release from these N sources. Melamine and ammeline would not maintain adequate turf quality when used as the sole source of N or in a 1:1 ratio of N with urea