Nitrous oxide emissions from arable soils in Germany — An evaluation of six long-term field experiments

In this study emissions of N2O from arable soils are summarized using data from long-term N2O monitoring experiments. The field experiments were conducted at six sites in Germany between 1992 and 1997. The annual N-application rate ranged from 0 to 350 kg N ha—1. Mineral and organic N-fertilizer applications were temporarily split adapted to the growth stage of each crop. N-fertilizer input and N-yield by the crops were used to calculate the In/Out-balance. The closed chamber technique was applied to monitor the N2O fluxes from soil into the atmosphere. If possible, plants were included in the covers. Annual N2O emission values were based on flux rate measurements of an entire year. The annual N2O losses ranged from 0.53 to 16.78 kg N2O-N ha—1 with higher N2O emissions from organically fertilized plots as compared to minerally fertilized plots. Approximately 50% of the total annual emissions occurred during winter. No significant relationship between annual N2O emissions and the respective N-fertilization rate was found. This was attributed to site- and crop-specific effects on N2O emission. The calculation of the N2O emission per unit N-yield from winter cereal plots indicates that the site effect on N2O emission is more important than the effect of N-fertilization. From unfertilized soils at the sites Braunschweig and Timmerlah a N-yield of 60.0 kg N ha—1 a—1 and N2O emissions of 2 kg N ha—1 a—1 were measured. This high background emission was assigned to the amount and turnover of soil organic matter. For a crop rotation at the sites Braunschweig and Timmerlah the N In/Out-balance over a period of four years was identified as a suitable predictor of N2O emissions. This parameter characterizes the efficiency of N-fertilization for crop production and allows for N-mineralization from the soil.