NITROUS-OXIDE EMISSIONS FROM A FALLOW AND WHEAT FIELD AS AFFECTED BY INCREASED SOIL TEMPERATURES

In order to determine the effects of increased soil temperature result ing from global warming on microbiological reactions, a 21-month field experiment was carried out in the Bavarian tertiary hills. The major objective was to focus on N2O releases as either a positive or negativ e feedback in response to global warming. The soils of a fallow field and a wheat field were heated 3 degrees C above ambient temperature an d N2O fluxes were measured weekly from June 1994 to March 1996, During the experimental period, measured temperature differences between the control plots and the heated plots were 2.9+/-0.3 degrees C at a dept h of 0.01m and 1.0-1.8 degrees C at a depth of 1 m, Soil moisture decr eased with the elevated soil temperatures of the heated plots, The mea n differences in soil moisture between the treatments were 6.4% (fallo w field) and 5.2%(DW) (wheat field dry weight, DW), respectively. Over all N2O releases during the experimental period from the fallow field were 4.8 kg N2O-N ha(-1) in the control plot against 5.0 kg N2O-N ha(- 1) in the heated plot, and releases from the wheat field were 8.0 N2O- N ha(-1) in the control plot and 7.6 N2O-N kg ha(-1) in the heated plo t. However, on a seasonal basis, cumulated N2O emissions differed betw een the plots. During the summer months (May-October), releases from t he heated fallow plot were 3 times the rates from the control plot. in the winter months, N2O releases increased in both the fallow and whea t fields and were related to the number of freezing and thawing cycles .