Main Driving Variables and Effect of Soil Management on Climate or Ecosystem-Relevant Trace Gas Fluxes from Fields of the FAM

This chapter discusses the main driving variables and effect of soil management on climate or ecosystem-relevant trace gas fluxes from fields of the Forschungsverbund Agrarökosysteme München (FAM). Nitrous oxide (N₂O) production rates during nitrification and denitrification rise with increasing soil temperature. High N₂O emission from agricultural soils mainly results from the increased nitrogen (N) input into agricultural soils through N fertilizers, organic fertilizers and N accumulation by legumes. Nitrification mainly occurs in well-aerated soil compartments and is consequently the main source of N₂O in dry and fresh soils. Soil moisture is identified as one of the most important driving variables for N₂O fluxes from arable soils, showing a high temporal variability. At soil moisture contents above field capacity, N₂O is further reduced to N₂ by denitrification resulting in a decrease of the N₂O flux rates. Positive correlations between the soil nitrate contents and the N₂O emissions have numerously been reported from study sites where denitrification is shown to be the main N₂O source. Most investigations on N₂O emissions from arable and grassland soils at the FAM research station reveal positive relationships with soil nitrate contents and soil moisture data of the topsoil. Trace gas flux determination at the FAM research station shows extremely high flux rates during the cold winter months. It is shown that the N₂O background emission during expanded periods of severe soil frost is higher as compared to the background emission during the summer period. The results of all investigations on N₂O emissions at FAM sites reveal strong positive correlations between soil moisture and the N₂O flux rates.