RESUMO
Changing precipitation has the potential to alter nitrous oxide (N2 O) emissions from agricultural regions. In this study, we applied the Coupled Model Intercomparison Project Phase 5 end-of-century RCP 8.5 (business as usual) precipitation projections for the U.S. Upper Midwest and examined the effects of mean precipitation changes, characterized by increased early-season rainfall and decreased mid- to late-season rainfall, on N2 O emissions from a conventionally managed corn (Zea mays L.) cropping system grown in an indoor mesocosm facility over four growing seasons. We also assessed the response of N2 O emissions to over 1,000 individual rain events. Nitrous oxide emissions were most strongly correlated with water-filled pore space (WFPS) and soil nitrogen (N) status. After rain events, the change in N2 O emissions, relative to pre-rain emissions, was more likely to be positive when soil NO3 - was >40 mg N kg-1 soil and soil NH4 + was >10 mg N kg-1 soil and was more likely to be negative when soil NO3 - was >40 mg N kg-1 soil and soil NH4 + was <10 mg N kg-1 soil. Similarly, hourly N2 O emissions remained <5 nmol m- 2 s-1 when combined NH4 + + NO3 - was <20 mg N kg-1 soil or NH4 + and NO3 - were <5 and 20 mg N kg-1 soil, respectively. Rain event magnitude did not substantially affect the change in N2 O flux. Finally, growing-season N2 O emissions, soil moisture, and inorganic N content were not affected by the future precipitation pattern. Near-optimal soil WFPS combined with soil N concentrations above the identified thresholds favor higher N2 O emissions.
