MANAGEMENT AND UREASE INHIBITOR EFFECTS ON NITROGEN USE EFFICIENCY INNO-TILL CORN

No-till corn (Zea mays L.) production is common in the Mid-Atlantic re gion and urea-ammonium nitrate solution (UAN) and urea are by far the most common N fertilizers used in the region. Because of the potential for ammonia volatilization from these sources when they are surface-a pplied to no-till corn, it is necessary to know how the method and tim e of application affect the N fertilizer use efficiency (grain yield, N uptake, and ear-leaf N concentration per pound of N applied) obtaine d with them. We also wanted to determine if the urease inhibitor amend ments ammonium thiosulfate (ATS) and N-(n-butyl) thiophosphoric triami de (NBPT) would increase the N fertilizer use efficiency of UAN and ur ea surface applied to no-till corn. Field experiments were conducted f or 3 yr in central Pennsylvania on well-drained silt loam soils. Ther e were three N rates, 50, 100, and 150 lb N/acre. Averaged over the 3 yr and three rates, broadcast urea and sprayed UAN at planting general ly produced significantly lower N fertilizer use efficiency than at-pl ant dribbled UAN and broadcast ammonium nitrate, and sidedress applica tions of dribbled or injected UAN. Nitrogen fertilizer use efficiency of UAN applied to no-till corn was in the order: at-plant spray < at-p lant band < sidedress band < sidedress inject. Amending UAN with ATS h ad no significant effect on N fertilizer use efficiency of sprayed UAN and only a slight effect on banded UAN. Amending UAN with the urease inhibitor NBPT produced significantly greater N fertilizer use efficie ncy with the sprayed UAN. Amending urea with 0.5% NBPT also significan tly increased the N fertilizer use efficiency of unincorporated broadc ast and banded urea.