Effects of nitrogen input and grazing on methane fluxes of extensively andintensively managed grasslands in the Netherlands

Generally, grasslands are considered as sinks for atmospheric CH4, and N in put as a factor reduces CH4 uptake by soils. We aimed to assess the short- and long-term effects of a wide range of N inputs, and of grazing versus mo wing,on net CH4 emissions of grasslands in the Netherlands. These grassland s are mostly intensively managed with a total N input via fertilisation and atmospheric deposition in the range of 300-500 kg N ha(-1) year(-1). Net C H4. emissions were measured with vented, closed flux chambers at four contr asting sites, which were chosen to represent a range of N inputs. There wer e no significant effects of grazing versus mowing, stocking density, and wi thholding N fertilisation for 3-9 years, on net CH4 emissions. When the gro und-water level was close to the soil surface, the injection of cattle slur ry resulted in a significant net CH4 production. The highest atmospheric CH 4 uptake was found at the site with the lowest. N input and the lowest grou nd-water level, with an annual CH4, uptake of 1.1 kg CH4 ha(-1) year(-1). T his is assumed to be the upper limit of: CH4 uptake by grasslands in the Ne therlands. We conclude that grasslands in the Netherlands are a net sink of CH4, with sin estimated CH4 uptake of 0.5 Gg CH4 year(-1). Ar the current rates of total N input, the overall effect of N fertilisation on net CH4 em issions from grasslands is thought to be small or negligible.