Publication date: 15 January 2018
Source:Geoderma, Volume 310
Author(s): Jens Tierling, Hermann Kuhlmann
The potential of nitrogen (N) fertilizer forms to mitigate N2 O emissions from agricultural fields is not very well understood. It is known that both reduced and oxidized N forms can be beneficial, depending on site-specific edaphic and climatic conditions. In the present study four laboratory incubation experiments were conducted under conditions that should minimize denitrification to investigate N2 O emissions during the nitrification of solid N fertilizers. It was found that on two loamy sand soils with pH values slightly above pH2 O emissions than ammonium sulphate (AS). N2 O emission rates from urea were accompanied by elevated soil nitrite levels, while those of AS were not. The direct addition of a NaNO2 solution revealed an exponential relationship between soil nitrite levels and cumulative N2 O emissions, indicating that soil nitrite induces N2 O emissions, probably by nitrite reduction via nitrifier denitrification. When the soil pH was increased to 6.3 (soil from a long-term liming experiment) nitrite accumulation during nitrification was observed for both N forms. Cumulative N2 O emissions did not differ between N forms on the latter soil, but N2 O emission kinetics were faster for urea. Cumulative N2 O emissions from AS at soil pH It was concluded that i) nitrite accumulation during nitrification of reduced N fertilizer forms can significantly contribute to N2 O emissions under non-denitrifying conditions, ii) the risk of nitrite accumulation increases with higher soil pH values, and iii) that the alkalizing hydrolysis of urea increases the risk of nitrite accumulation and thus higher N2 O emissions as well. This mechanism would explain why urea causes higher N2 O emissions than fertilizers in the form of ammonium salts.
Source:Geoderma, Volume 310
Author(s): Jens Tierling, Hermann Kuhlmann