Enhanced-efficiency nitrogen fertilizers reduce winter losses of nitrous oxide, but not of ammonia, from no-till soil in a subtropical agroecosystem

Nitrogen (N) gas losses can be reduced by using enhanced-efficiency N (EEN) fertilizers such as urease inhibitors and coating technologies. In this work, we assessed the potential ofEENfertilizers to reduce winter losses of nitrous oxide (N2O-N) and ammonia (NH3-N) from a subtropical field experiment on a clayey Inceptisol under no-till in Southern Brazil. TheEENsources used included urea containingN-(n-butyl) thiophosphoric triamide (UR+NBPT), polymer-coated urea (P-CU) and copper-and-boron-coated urea (CuB-CU) in addition to common urea (UR) and a control treatment without N fertilizer application. N2O-N andNH(3)-N losses were assessed by using the static chamber method and semi-open static collectors, respectively. Both N2O-N andNH(3)-N exhibited two large peaks with an intervening period of low soil moisture and air temperature. Although the short-term effect was limited to the first few days after application,UR +NBPTurea decreased soil N2O-N emissions by 38% relative toUR. In contrast, urease inhibitor technology had no effect onNH(3)-N volatilization. Both coating technologies (CuB-CUand P-CU) were ineffective in reducing N losses via N2O production orNH(3)volatilization. The N2O emission factor (% N applied released as N2O) was unaffected by all N sources and amounted to only 0.48% of N applied-roughly one-half the default factor ofIPCCTier 1 (1%). Based on our findings, usingNBPT-treated urea in the cold winter season in subtropical agroecosystems provides environmental benefits in the form of reduced soil N2O emissions; however, fertilizer coating technologies provide no agronomic (NH3) or environmental (N2O) advantages.