SHORT COMMUNICATION: Volatile losses of NH3 from surface-applied urea and urea ammonium nitrate with and without the urease inhibitors NBPT or ammonium thiosulphate

Abstract

Field microplot studies were conducted under zero-till conditions on a fine sandy loam (Orthic Black Chernozem) to determine the effect of the urease inhibitors N-(n-butyl) thiophosphoric triamide (NBPT) and ammonium thiosulphate (ATS) on volatile losses of NH3 from urea and urea ammonium nitrate (UAN). Two studies were conducted, one in late May and one in early August. Losses of NH3 were measured on days 1, 2, 4 and 7 after fertilizer application, using ammonia traps. Ammonia losses were higher in the second study due to the higher soil temperatures and lower soil moisture later in the growing season. Total NH3 losses increased in the order Control < UAN + NBPT = Urea + NBPT < UAN + ATS = UAN < Urea. Total loss of NH3 during the 7 d after fertilizer application was higher from urea than from UAN, particularly in the first study. 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 time for rainfall to carry the urea into the soil, thus reducing total volatilization losses from surface fertilizer application. Key words: N-(n-butyl) thiophosphoric triamide, zero tillage