Anhydrous ammonia (AA) is a major fertilizer source in North America that can promote greater emissions of nitrous oxide (N 2O) than other nitrogen (N) fertilizers. Previous studies found that injection of AA at a shallow depth (0.1 m) decreased N 2O in a rainfed clay loam but increased N 2O in an irrigated loamy sand compared with the standard injection depth of 0.2 m. The objective of this study was to evaluate the effects of AA injection depth in a silt loam soil used for corn ( Zea mays L.) production and managed under two contrasting tillage regimes over two consecutive growing seasons (2010 and 2011) in Minnesota. In contrast with previous studies, AA placement depth did not affect N 2O emissions in either tillage system or in either growing season. Tillage by itself affected N 2O emissions only in the drier of two seasons, during which N 2O emissions under no tillage (NT) exceeded those under conventional tillage (CT) by 55%. Soil moisture content under NT was also greater than under CT only in the drier of the two seasons. Effects of AA placement depth and long-term tillage regime on N 2O emissions exhibit intersite as well as interannual variation, which should be considered when developing N 2O mitigation strategies. Further study is needed to identify specific soil, climate, or other factors that mediate the contrasting responses to management practices across sites.
