Evidence of increasing atmospheric carbon dioxide (CO2) levels has prompted research into ways to sequester atmospheric CO2. It has been suggested that converting agricultural ecosystems from conventional tillage to reduced or no tillage systems could possibly reduce atmospheric CO2 by increasing soil carbon (C) levels. Unfortunately, current research into the problem has produced conflicting results. Furthermore, few studies have considered changes in methane (CH4) and nitrous oxide (N2O) fluxes, which could potentially offset any gains resulting from increases in soil C. During the summers of 2004 and 2005, chamber and micrometeorological techniques were used to measure soil CO2, CH4, and N2O fluxes from two fields grown using contrasting management strategies in Rosemount, Minnesota, USA. Both fields represent corn/soybean rotation agriculture in the Upper Midwest. During 2004 and 2005, the fields were planted with soybeans and corn, respectively. One field was farmed conventionally (CONV) with fall chisel/disk tillage after each harvest (typical in the Upper Midwest). The alternative (ALT) field was farmed using reduced tillage (strip till) after harvest and a spring oats cover crop. During 2005, anhydrous ammonia was knifed into the CONV field and urea was broadcast on the ALT field. In conjunction with the soil chamber measurements, CO2 fluxes were measured using eddy covariance and N2O fluxes were measured using a tunable diode laser (TDL) and flux gradient method. Nighttime flux measurements obtained using micrometeorological methods were compared to the chamber measurements in order to better constrain ecosystem respiration. Our preliminary results indicate that there was not a significant difference (p < 0.05) in CO2 fluxes between tillage treatments for either 2004 or 2005. CO2 fluxes for each year were 2.4 ± 0.26 µmol m-2 s-1 and 2.6 ± 0.18 µmol m-2 s-1 for the ALT field and 2.2 ± 0.19 µmol m-2 s-1 and 2.8 ± 0.17 µmol m-2 s-1 for the CONV field during 2004 and 2005, respectively. N2O fluxes were not significantly different between treatments for 2004 or 2005. In 2004, the ALT and CONV N2O fluxes were 2.1 x 10-4 ± 5.4 x 10-5 µmol m-2 s-1 and 1.3 x 10-4 ± 3.5 x 10-5 µmol m-2 s-1, respectively. In 2005, the ALT and CONV N2O fluxes were 7.4 x 10-4 ± 2.1 x 10-4 µmol m-2 s-1 and 1.1 x 10-3 ± 2.4 x 10-4 µmol m-2 s-1, respectively. CH4 fluxes were significantly different in 2004, with mean fluxes of -3.0 x 10-4 ± 5.7 x 10-5 µmol m-2 s-1 and -1.0 x 10-5 ± 6.2 x 10-5 µmol m-2 s-1 for the ALT and COVN fields, respectively. CH4 fluxes were not significantly different in 2005. These results suggest that management practices did not significantly affect the greenhouse gas budget, with the exception of CH4 in 2004. However, the overall magnitude of the CH4 fluxes was negligible in these systems. Annual budgets of these trace gases are required in order to assess the greenhouse gas potential of these systems.
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