SPRING-APPLIED NITROGEN-FERTILIZER INFLUENCE ON WINTER-WHEAT AND RESIDUAL SOIL NITRATE

Spring fertilization may reduce N losses and immobilization compared w ith fall-applied N in winter wheat (Triticum aestivum L.) grain produc tion systems, The objectives of this experiment were to determine the effects of spring applications of varying rates of three N fertilizer sources on grain yield and N concentration, and residual soil profile ammonium-N and nitrate-N distribution. Anhydrous ammonia (AA), urea-am monium nitrate (UAN), and UAN + dicyandiamide (DCD) (1% w/w N as DCD) were applied for three consecutive years on a sandy loam soil (Udic Ar giustoll). Nitrogen was applied prior to reproductive growth at 30, 60 , and 90 lb N/acre. An unfertilized check and an AA applicator check ( 0 N applied) were included, Anhydrous ammonia was injected in 18 in. b ands using a rolling coulter applicator. The UAN and UAN + DCD mixture were broadcast sprayed. Soil cores were taken to 4 ft from each plot after harvest. Core samples were partitioned by depth and analyzed to determine ammonium-N and nitrate-N. Grain yield responses to applied N were observed, No significant grain yield reduction was attributed to wheat disturbance by the AA applicator, Grain N uptake and apparent f ertilizer N recovery in the grain (based on the difference method) wer e greater for AA than for UAN. Anhydrous ammonia resulted in significa ntly greater upper profile soil nitrate-N than either UAN or UAN + DCD in 1 yr, Postemergence injection of AA into established winter wheat was an effective method for applying N when compared with broadcast UA N. Addition of DCD to UAN did not significantly affect measured plant or soil parameters.