| Abstrakt: |
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 (N2O) and methane ( CH4) 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 N2O and CH4 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 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 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. [ABSTRACT FROM AUTHOR] |
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