Two-year field study on the emission of N2O from coarse and middle-textured Belgian soils with different land use

In the following study N2O emissions from 3 different grasslands and from 3 different arable lands, representing major agriculture areas with different soil textures and normal agricultural practices in Belgium, have been monitored for 1 to 2 years. One undisturbed soil under deciduous forest was also included in the study. Nitrous oxide emission was measured directly in the field from vented closed chambers through photo-acoustic infrared detection. Annual N2O emissions from the arable lands ranged from 0.3 to 1.5 kg N ha(-1) y(-1) and represent 0.3 to 1.0% of the fertilizer N applied. Annual N2O emissions from the intensively managed grasslands and an arable land sown with grass were significantly larger than those from the cropped arable lands. Emissions ranged from 14 to 32 kg N ha(-1) y(-1), representing fertilizer N losses between 3 and 11%. At the forest soil a net N2O uptake of 1.3 kg N2O-N ha(-1) was recorded over a 2-year period. It seems that the N2O-N loss per unit of fertilizer N applied is larger for intensively managed and heavily fertilized (up to 500 kg N ha(-1)) grasslands than for arable lands and is substantially larger than the 1.25% figure used for the global emission inventory. Comparison of the annual emission fluxes from the different soils also indicated that land use rather than soil properties influenced the N2O emission. Our results also show once again the importance of year-round measurements for a correct estimate of N2O losses from agricultural soils: 7 to 76% of the total annual N2O was emitted during the winter period (October-February). Disregarding the emission during the off-season period can lead to serious underestimation of the actual annual N2O flux.