Response of nitrous oxide emissions to individual rain events and future changes in precipitation
Lee T. Miller, Timothy J. Griffis, Matthew Erickson, Peter Turner, M. J. Deventer, Zichong Chen, Zhongjie Yu, Rodney T. Venterea, John M. Baker, Alexander L. Frie
Abstract
Abstract Changing precipitation has the potential to alter nitrous oxide (N 2 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 N 2 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 N 2 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 N 2 O emissions, relative to pre‐rain emissions, was more likely to be positive when soil NO 3 – was >40 mg N kg –1 soil and soil NH 4 + was >10 mg N kg –1 soil and was more likely to be negative when soil NO 3 – was >40 mg N kg –1 soil and soil NH 4 + was <10 mg N kg –1 soil. Similarly, hourly N 2 O emissions remained <5 nmol m – 2 s –1 when combined NH 4 + + NO 3 – was <20 mg N kg –1 soil or NH 4 + and NO 3 – were <5 and 20 mg N kg –1 soil, respectively. Rain event magnitude did not substantially affect the change in N 2 O flux. Finally, growing‐season N 2 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 N 2 O emissions.