Response of nitrous oxide emissions to individual rain events and future changes in precipitation

Changing precipitation has the potential to alter nitrous oxide (N2O) 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 N2O 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 N2O 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 N2O 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 N2O emissions remained (-)(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 N2O flux. Finally, growing-season N2O 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 N2O emissions.