Nitrous oxide emissions from temperate grassland ecosystems in the Northern and Southern Hemispheres

Nitrogen (N) fertilized or grazed grasslands in temperate regions of the Northern and Southern Hemisphere are important sources for atmospheric nitrous oxide (N2O). Following synthetic urine applications in a New Zealand grassland ecosystem, and ammonium (NH4 +) and nitrate (NO3 -) applications to a German grassland ecosystem, approximately 31, 16, and 5%, respectively, of the total emitted N2O (N2Otot) was produced by nitrification (N2Onit) with the rest being produced by denitrification (N2Oden). Analyses of the combined data set showed that 75% of all N2O emissions occurred above 60% water filled porosity (WFPS) and that more than 80% of all N2O emissions occurred at soil temperatures between 10° and 15 C. N2Oden emissions were associated with a WFPS value at around 80% at relatively low NO3 - concentrations, while N2Onit emissions only occurred at high NH4 + levels shortly after N application at soil temperatures around 10 C. To increase the accuracy of predictions with simple mathematical models, such as the “hole-in-the-pipe-model,” long-term validation data sets are needed where driving variables are related to measured N2Onit and N2Oden data.