UREA NITRICPHOSPHATE FOR COOL-SEASON GRASS PRODUCTION

Significant losses of nitrogen (N) can occur via volatilization of amm onia (NH3) when non-incorporated broadcast applications of urea or ure a-containing fertilizers are made. This study was conducted to determi ne the efficacy of urea nitricphosphate (UNP) as an N and phosphorus ( P) source for cool-season grasses and to evaluate NH3 volatilization p otential of UNP as compared to urea under laboratory conditions. A thr ee-year field study compared UNP to ammonium nitrate (AN) and urea at 56 and 112 kg N/ha for tall fescue (Festuca arundinacea Schreb.) and s mooth brome (Bromus inermis Leyss.). Brome yields were significantly h igher from UNP as compared to urea for one of the three years. No such differences occurred with fescue. Nitrogen uptake was significantly h igher from UNP as compared to urea for one year each for brome and fes cue. Phosphorus uptake by brome was significantly higher from UNP as c ompared to urea for two years. Laboratory incubation studies showed si gnificantly lower NH3 volatilization from UNP than from urea after sev en days, but no significant differences after 14 days. The delay in NH 3 volatilization was due to the diffusion and subsequent hydrolysis of urea immediately below the soil zone initially influenced by the UNP. The reduction in NH3 volatilization at the early time could partially be attributed to an inhibition of urea hydrolysis and significantly l ower soil pH values for UNP as compared to urea in the upper 30 mm of soil cores. The general conclusion from the field and laboratory work was that UNP is a suitable N source for cool-season grasses, with the primary potential benefit being delayed NH3 volatilization as compared to urea.