Long‐term no‐till and stover retention each decrease the global warming potential of irrigated continuous corn

Over the last 50 years, the most increase in cultivated land area globally has been due to a doubling of irrigated land. Long‐term agronomic management impacts on soil organic carbon ( SOC ) stocks, soil greenhouse gas ( GHG ) emissions, and global warming potential ( GWP ) in irrigated systems, however, remain relatively unknown. Here, residue and tillage management effects were quantified by measuring soil nitrous oxide (N 2 O) and methane ( CH 4 ) fluxes and SOC changes (Δ SOC ) at a long‐term, irrigated continuous corn ( Zea mays L.) system in eastern Nebraska, United States. Management treatments began in 2002, and measured treatments included no or high stover removal (0 or 6.8 Mg DM ha −1 yr −1 , respectively) under no‐till ( NT ) or conventional disk tillage ( CT ) with full irrigation ( n = 4). Soil N 2 O and CH 4 fluxes were measured for five crop‐years (2011–2015), and Δ SOC was determined on an equivalent mass basis to ~30 cm soil depth. Both area‐ and yield‐scaled soil N 2 O emissions were greater with stover retention compared to removal and for CT compared to NT , with no interaction between stover and tillage practices. Methane comprised <1% of total emissions, with NT being CH 4 neutral and CT a CH 4 source. Surface SOC decreased with stover removal and with CT after 14 years of management. When Δ SOC , soil GHG emissions, and agronomic energy usage were used to calculate system GWP , all management systems were net GHG sources. Conservation practices ( NT , stover retention) each decreased system GWP compared to conventional practices ( CT , stover removal), but pairing conservation practices conferred no additional mitigation benefit. Although cropping system, management equipment/timing/history, soil type, location, weather, and the depth to which Δ SOC is measured affect the GWP outcomes of irrigated systems at large, this long‐term irrigated study provides valuable empirical evidence of how management decisions can impact soil GHG emissions and surface SOC stocks.