Nitrous oxide emissions from a fallow and wheat field as affected by increased soil temperatures

Abstract

In order to determine the effects of increased soil temperature resulting 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 negative feedback in response to global warming. The soils of a fallow field and a wheat field were heated 3 °C above ambient temperature and 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 °C at a depth of 0.01 m and 1.0–1.8 °C at a depth of 1 m. Soil moisture decreased with the elevated soil temperatures of the heated plots. The mean differences in soil moisture between the treatments were 6.4% (fallow field) and 5.2%DW (wheat field dry weight, DW), respectively. Overall 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 plot. However, on a seasonal basis, cumulated N2O emissions differed between the plots. During the summer months (May–October), releases from the heated fallow plot were 3 times the rates from the control plot. In the winter months, N2O releases increased in both the fallow and wheat fields and were related to the number of freezing and thawing cycles.