Technical Abstract: A no-till (NT) irrigated production system has potential to reduce soil erosion, fossil fuel consumption, and greenhouse gas emissions compared with a conventional till (CT) system. Tillage system and N fertilization effects on soil organic C (SOC) sequestration, greenhouse gas emissions, and global warming potential (GWP) in irrigated production systems are not well documented. A study was initiated on a Fort Collins clay loam (classified as fine-loamy, mixed, superactive, mesic Aridic Haplustalfs) in northeastern Colorado near Fort Collins, USA (40 degrees 39’ N; 104 degrees 59’ W; 1530 m a.s.l.) in 1999 with six N rates (0, 34, 67, 101, 134, and 224 kg N/ha) to investigate the potential of NT management to sequester SOC while maintaining continuous corn (Zea mays L.) yields at levels similar to CT practices. In April 2002, measurement of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from three of the N rates (0, 134, and 224 kg N/ha) were initiated in the NT and CT systems. Fluxes of CO2, CH4, and N2O were measured, using vented chambers, one to three times per week, year round, from April 2002 through October 2004. Methane fluxes were small and did not differ between tillage treatments, but varied with year. Carbon dioxide efflux was higher in CT compared to NT in 2002, but was not different by tillage treatment in 2003 and 2004. Nitrous oxide fluxes increased linearly with increasing N-fertilizer rate each year with emission rates varying with year but not by tillage treatment. Grain yields and crop residue increased with increasing N rate in both tillage systems, but grain yields were slightly higher in CT than in NT system. The lower grain yield with NT probably resulted from the slow early spring development and delayed tasseling compared with the CT system as a result of cooler spring soil temperatures in the NT system. Grain yields were near maximum with an available N (soil + fertilizer N) level of 276 and 268 kg N/ha in the CT and NT systems, respectively. Corn residue increased with increasing N rate with no difference in residue production between tillage systems. The NT system had the same size plant for grain production as the CT system. Trends were for SOC to be increasing in the NT system but remaining fairly constant in the CT system. Based on soil C sequestration, only NT soils were net sinks for GWP. No-till soils were greater net sinks for GWP when adequate fertilizer was added to maintain crop production than CT soils. The results suggest that economic viability and environmental conservation can be achieved by minimizing tillage and utilizing appropriate levels of fertilizer to optimize crop yields.