Carbon dioxide balance of a crop-fallow rotation in western Canada

The use of micrometeorological and chamber techniques is a unique means to investigate the seasonal CO2 cycle in agriculture. Two growing seasons are reported in this study, one being a wet year (207 mm 1994) and the other a dry year (86 mm 1996). A Bowen ratio tower and automated soil chambers were set up in a barley and fallow field to simultaneously monitor energy and c arbon dioxide fluxes. These fluxes were integrated over the measurement per iod to arrive at a seasonal carbon balance of each surface. Our results sho w that barley removed CO2 from the atmosphere, amounting to -9.5 and -8.5 M g CO2 ha(-1) in 1994 and 1996, respectively. A portion of the atmospheric C O2 was retained by the soil (6.6 and 3.7 Mg CO2 ha(-1) in 1994 and 1996, re spectively). The soil in fallow emitted -11.1 and -6.7 Mg CO2 ha(-1) in 199 4 and 1996, respectively. Above a crop-fallow area. the atmosphere gained C O2 from the surface in 1994 (0.8 Mg CO, ha(-1)) but was a source of CO2 in 1996 (losing -1 Mg CO2 ha(-1) to the surface). The soil under a crop-fallow area lost CO2 in both years (-2.2 and -1.5 Mg CO2 ha(-1) in 1994 and 1996, respectively).