VOLATILE LOSSES OF NH3 FROM SURFACE-APPLIED UREA AND UREA AMMONIUM-NITRATE WITH AND WITHOUT THE UREASE INHIBITORS NBPT OR AMMONIUM THIOSULFATE

Field microplot studies were conducted under zero-till conditions on a fine sandy loam (Orthic Black Chernozem) to determine the effect of t he urease inhibitors N-(n-butyl) thiophosphoric triamide (NBPT) and am monium thiosulphate (ATS) on volatile losses of NH3 from urea and urea ammonium nitrate (UAN). Two studies were conducted, one in late May a nd one in early August. Losses of NH3 were measured on days 1, 2, 4 an d 7 after fertilizer application, using ammonia traps. Ammonia losses were higher in the second study, due to the higher soil temperatures a nd lower soil moisture later in the growing season. Total NH3 losses i ncreased in the order Control < UAN + NBPT = Urea + NBPT < UAN + ATS = UAN < Urea. Total loss of NH3 during the 7 d after fertilizer applica tion was higher from urea than from UAN, particularly in the first stu dy. Use of NBPT was effective in reducing NH3 volatilization from both UAN and urea during 7 d after fertilizer application while use of ATS had little influence on NH3 loss from UAN. The NBPT may delay losses by slowing the hydrolysis of urea, but volatilization may persist for a longer duration. The delay in urea hydrolysis could allow rime for r ainfall to carry the urea into the soil, thus reducing total volatiliz ation losses from surface fertilizer application.