NITROUS-OXIDE AND METHANE FLUXES FROM ORGANIC SOILS UNDER AGRICULTURE

Trace gas fluxes of N2O and CH4 were measured weekly over 12 months on cultivated peaty soils in southern Germany using a closed chamber tec hnique. The aim was to quantify the effects of management intensity an d of soil and climatic factors on the seasonal variation and the total annual exchange rates of these gases between the soil and the atmosph ere. The four experimental sites had been drained for many decades and used as meadows (fertilized and unfertilized) and arable land (fertil ized and unfertilized), respectively. Total annual N2O-N losses amount ed to 4.2, 15.6, 19.8 and 56.4 kg ha(-1) year(-1) for the fertilized m eadow, the fertilized field, the unfertilized meadow and the unfertili zed field, respectively. Emission of N2O occurred mainly in the winter when the groundwater level was high. At all sites maximum emission ra tes were induced by frost. The largest annual N2O emission by far occu rred from the unfertilized field where the soil pH was low (4.0). At t his site 71% of the seasonal variation of N2O emission rates could be explained by changes in the groundwater level and soil nitrate content . A significant relationship between N2O emission rates and these fact ors was also obtained for the other sites, which had a soil pH between 5.1 and 5.8, though the relation was weak (R-2 = 15-27%). All sites w ere net sinks for atmospheric methane. Up to 78% of the seasonal varia tion in CH4 flux rates could be explained by changes in the groundwate r level. The total annual CH4-C uptake was significantly affected by a gricultural land use with greater CH4 consumption occurring on the mea dows (1043 and 833 g ha(-1)) and less on the cultivated fields (209 an d 213 g ha(-1)).