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

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.
(© 2022 The Authors. Journal of Environmental Quality published by Wiley Periodicals LLC on behalf of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)