NITROUS-OXIDE FLUXES FROM GRASSLAND IN THE NETHERLANDS .2. EFFECTS OFSOIL TYPE, NITROGEN-FERTILIZER APPLICATION AND GRAZING

Intensively managed grasslands are potentially a large source of nitro us oxide (N2O) in the Netherlands because of the large nitrogen (N) in put and the fairly wet soil conditions. To quantify the effects of soi l type, N-fertilizer application and grazing on total N2O losses from grassland, fluxes of N2O were measured weekly from unfertilized and mo wn, N fertilized and mown, and N fertilized and predominantly grazed g rassland on a sand soil, a clay soil, and two peat soils during the gr owing season of 1992. Total N2O losses from unfertilized grassland wer e 2.5-13.5 times more from the peat soils than from the sand and clay soils. Application of calcium ammonium nitrate fertilizer significantl y increased N2O flux on all sites, especially when the soil was wet. T he percentage of fertilizer N applied lost to the atmosphere as N2O du ring the season ranged from 0.5 on the sand soil to 3.9 on one of the peat soils. Total N2O losses were 1.5-2.5 times more from grazed grass land than from mown grassland, probably because of the extra N input f rom urine and dung. From 1.0 to 7.7% of the calculated total amount of N excreted in urine and dung was emitted as N2O on grazed grassland. The large N2O losses measured from the peat soils, combined with the l arge proportion of grassland on peat in the Netherlands, mean that the se grasslands contribute significantly to the total emission from the country.