Cropping and tillage management can increase atmospheric CO{sub 2}, N{sub 2}O, and CH{sub 4} concentrations, and contribute to global warming and destruction of the ozone layer. Fluxes of these gases in vented surface chambers, and water-filled pore space (WFPS) and temperature of surface soil were measured weekly from a long-term winter wheat (Triticum aestivum L.)-fallow rotation system under chemical and mechanical tillage follow management and compared with those from native grass sod at Sidney, NE, from March 1993 to July 1995. Cropping, tillage, within-field location, time of year, soil temperature, and WFPS influenced net greenhouse gas fluxes. Mean annual interrow CO{sub 2} emissions from wheat-fallow ranged from 6.0 to 20.1 kg C ha{sup {minus}1} d{sup {minus}1} and generally increased with intensity and degree of tillage. Nitrous oxide flux averaged autumn > winter. Winter periods accounted for 4 to 10% and 3 to 47% of the annual CO{sub 2} and N{sub 2}O flux, respectively, and 12 to 21% of the annual CH{sub 4} uptake. Fluxes of CO{sub 2} and N{sub 2}O, and CH{sub 4} uptake increased linearly with soil temperature. No-till fallow exhibited the least threat to deterioration of atmospheric or soil quality as reflected by greater CH{sub 4} uptake, decreased N{sub 2}O and CO{sub w} emissions, and less loss of soil organic C than tilled soils. However, potential for increased C sequestration in this wheat-fallow system is limited due to reduced C input from intermittent cropping.« less