EFFECTS OF TYPE AND AMOUNT OF APPLIED NITROGEN-FERTILIZER ON NITROUS-OXIDE FLUXES FROM INTENSIVELY MANAGED GRASSLAND

Five field experiments and one greenhouse experiment were carried out to assess the effects of nitrogen (N) fertilizer type and the amount o f applied N fertilizer on nitrous oxide (N2O) emission from grassland. During cold and dry conditions in early spring, emission of N2O from both ammonium (NH4+) and nitrate (NO3-) containing fertilizers applied to a clay soil were relatively small, i.e. less than 0.1% of the N ap plied. Emission of N2O and total denitrification losses from NO3- cont aining fertilizers were large after application to a poorly drained sa nd soil during a wet spring. A total of 5-12% and 8-14% of the applied N was lost as N2O and via denitrification, respectively. Emissions of N2O and total denitrification losses from NH4+ fertilizers and cattle slurry were less than 2% of the N applied. Addition of the nitrificat ion inhibitor dicyandiamide (DCD) reduced N2O fluxes from ammonium sul phate (AS). However, the effect of DCD to reduce total N2O emission fr om AS was much smaller than the effect of using NH4+ fertilizer instea d of NO3- fertilizer, during wet conditions. The greenhouse study show ed that a high groundwater level favors production of N2O from NC3- fe rtilizers but not from NH4+ fertilizers. Increasing calcium ammonium n itrate (CAN) application increased the emitted N2O on grassland from 0 .6% of the fertilizer application rate for a dressing of 50 kg N ha(-1 ) to 3.1% for a dressing of 300 kg N ha(-1). In another experiment, N2 O emission increased proportionally with increasing N rate. The result s indicate that there is scope for reducing N2O emission from grasslan ds by choosing the N fertilizer type. depending on the soil moisture s tatus. Avoiding excessive N application rates may also minimize N2O em ission from intensively managed grasslands.