NITROGEN LOSS FROM GRASSLAND ON PEAT SOILS THROUGH NITROUS-OXIDE PRODUCTION

Nitrous oxide (N2O) in soils is produced through nitrification and den itrification. The N2O produced is considered as a nitrogen (N) loss be cause it will most likely escape from the soil to the atmosphere as N2 O or N-2. Aim of the study was to quantify N2O production in grassland on peat soils in relation to N input and to determine the relative co ntribution of nitrification and denitrification to N2O production. Mea surements were carried out on a weekly basis in 2 grasslands on peat s oil (Feat I and Feat II) for 2 years (1993 and 1994) using intact soil core incubations. In additional experiments distinction between N2O f rom nitrification and denitrification was made by use of the gaseous n itrification inhibitor methyl fluoride (CH3F). Nitrous oxide productio n over the 2 year period was on average 34 kg N ha(-1) yr(-1) for mown treatments that received no N fertiliser and 44 kg N ha(-1) yr(-1) fo r mown and N fertilised treatments. Grazing by dairy cattle on Feat I caused additional N2O production to reach 81 kg N ha(-1) yr(-1). The s ub soil (20-40 cm) contributed 25 to 40% of the total N2O production i n the 0-40 cm layer. The N2O production:denitrification ratio was on a verage about 1 in the top soil and 2 in the sub soil indicating that N 2O production through nitrification was important. Experiments showed that when ratios were larger than 1, nitrification was the major sourc e of N2O. In conclusion, N2O production is a significant N loss mechan ism in grassland on peat soil with nitrification as an important N2O p roducing process.