Nitrous oxide emissions from agricultural land use in Germany— a synthesis of available annual field data

Abstract

Abstract The nations that have ratified the Kyoto Protocol must set up an appropriate national inventory on N 2 O emissions from agricultural land use, in order to report properly on the achievements made in reducing greenhouse‐gas emissions. The search for the appropriate method is a controversial topic as it is subject to high uncertainty in particular associated to the upscaling from site measurements. In this study, all available data from Germany on annual N 2 O‐emission rates derived from field experiments of at least an entire year are summarized. From each study, only differences in soil properties on N input qualified as an individual data set. Under these premises, 101 treatments from 27 sites were found equally spread across Germany. The annual N application ranged from 0 to 400 kg N ha –1 and the annual emission rates from 0.04 to 17.1 kg ha –1 . Annual emission factors (EFs), uncorrected for background emission, varied considerably from 0.18% to 15.54% of N applied. There was no nationwide correlation found for the relationship between N 2 O losses and N application, soil C, soil N, soil texture, or soil pH. However, site‐specific trends in the relationship between emission factor and mean soil aeration status, as expressed by the soil type and/or mean climatic conditions, were revealed. Regularly water‐logged soils were characterized by low emission factors as were soils from the drier regions (<600 mm y –1 ), whereas well‐aerated soils from the frost‐intensive regions showed exceptionally high emission factors. Since purely physical and chemical parameterization failed to describe N 2 O emissions from agricultural land use on the national scale, there must be a biological adaptation to mean site conditions, i.e. , different microbial communities react differently to similar actual conditions in terms of N 2 O dynamics. Regardless of the point of view, the chapter on N 2 O soil dynamics cannot be closed yet, and new additional model concepts, process studies, and field measurements are needed.