The objective is to provide estimates of the soil and atmosphere exchange of nitrous oxide over Europe
A project was set up to provide estimates of the soil atmosphere exchange of nitrous oxide over Europe, identify the key soil and other environmental factors controlling gaseous fluxes, model fluxes over large regions and develop new methods of measuring gaseous fluxes. In particular:
to investigate the effects of nitrogen fertilizer form, and soil and environmental factors, on nitrous oxide fluxes from grassland;
to compare nitrous oxide flux measurements by various chamber methods and by flux gradient and eddy correlation micrometeorological methods, in a joint field campaign;
to develop further the tunable diode laser system for nitrous oxide measurement by eddy correlation and the automted chamber gas sampling system;
to measure nitrous oxide fluxes from non agricultural ecosystems, and to investigate spatial variability and topographically related trends in the fluxes.
After 2 joint field campaigns, it was concluded that satisfactory agreement was now attainable between micrometeorological methods and small chamber methods for for measuring nitrous oxide emissions, provided that care was taken to ensure that the footprint (the area measured) of the micrometeorological measurement, and the area measured with arrays of chambers, were substantially the same. Other work with chambers (including the development of battery-powered automated systems) provided information on fluxes from a variety of land uses. On agricultural land the timing and chemical form of nitrogen fertilizer addition had a major impact on the size of the nitrous oxide emissions. Soil temperature, wetness and mineral nitrogen content were the major controlling variables.
Measurements of nitrous oxide will be made initially by the well proven technique involving accumulation of the gas in a cover box over a small area of land surface and measurement of the concentration increase with time by gas chromatography (GC). Adequate replication and the use of automatic sampling and analysis will allow investigation of spatial and temporal variability of emissions. Results with both static (closed) and dynamic (open) boxes will be compared. At one site, the cover box method for nitrous oxide will also be compared, during the first year, with the mass balance method used by Denmead for ammonia.
At a later stage, analysis by GC used in both methods, including samples from greatly extended boxes (tunnels), will be compared with measurements by a new tunable diode laser (TDL) system developed as part of the project. Use of the TDL system will be extended to nitrous oxide flux measurements from natural wetlands.
Gaseous emission data will be complemented by the following soil measurements: temperature; water content and matrix potential; nitrous oxide and ammonia content; oxygen concentration; particle and aggregate size distributions; temperature and redox potential.
Funding SchemeCSC - Cost-sharing contracts
EH26 0QB Penicuik
1017 Koebenhavn K/copenhaegen