Long-Term No-Till And Stover Retention Each Decrease The Global Warming Potential Of Irrigated Continuous Corn

Abstract

Over the last 50ￂﾠyears, the most increase in cultivated land area globally has been due to a doubling of irrigated land. Long￢ﾀﾐ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 (N2O) and methane (CH4) fluxes and SOC changes (ￎﾔSOC) at a long￢ﾀﾐ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 6.8ￂﾠMgￂﾠDMￂﾠha￢ﾈﾒ1ￂﾠyr￢ﾈﾒ1, respectively) under no￢ﾀﾐtill (NT) or conventional disk tillage (CT) with full irrigation (nￂﾠ=ￂﾠ4). Soil N2O and CH4 fluxes were measured for five crop￢ﾀﾐyears (2011￢ﾀﾓ2015), and ￎﾔSOC was determined on an equivalent mass basis to ~30ￂﾠcm soil depth. Both area￢ﾀﾐ and yield￢ﾀﾐscaled soil N2O 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 CH4 neutral and CT a CH4 source. Surface SOC decreased with stover removal and with CT after 14ￂﾠyears of management. When ￎﾔ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 ￎﾔSOC is measured affect the GWP outcomes of irrigated systems at large, this long￢ﾀﾐterm irrigated study provides valuable empirical evidence of how management decisions can impact soil GHG emissions and surface SOC stocks.