Significant increases in nitrous oxide emissions under simulated extreme rainfall events and straw amendments from agricultural soil

Abstract

Pulsed N₂O emissions resulting from field management practices (N fertilization addition and straw return) or rainfall events make for a significant proportion of the total annual N₂O budget from croplands. However, it remains unclear whether altered rainfall patterns induced by climate change will stimulate the responses of pulsed N₂O emissions to various field practices. In this study, we aimed to elucidate the underlying mechanisms driving pulsed N₂O emissions in response to extreme rainfall events and examine their interaction with carbon and nitrogen availability. We hypothesized that highly available substrates rapidly induce an anaerobic environment and N₂O pulses during extreme rainfall events. A soil column experiment under simulating extreme rainfall events was conducted to investigate the responses of pulsed N₂O emissions to three common farming practices: nitrogen fertilization (N), nitrogen fertilization coupled with low straw return (N+LS), and nitrogen fertilization coupled with high straw return (N+HS). We frequently monitored surface emissions and soil concentrations of N₂O and CO₂, and measured O₂, NH₄⁺, NO₃^- and DOC concentrations. N and straw amendments together under simulated rainfall events significantly depleted O₂, and simultaneously increased pulsed N₂O emissions. The N+HS treatment exhibited the highest soil N₂O concentration (51.9 µL L⁻¹) and lowest O₂ concentration (4.3 %), along with high soil moisture levels (24.8 %–32.2 %). Correspondingly, the highest cumulative N₂O emissions were observed in the N+HS treatment (117.8 mg m⁻²), followed by 52.2, 31.9, and 11.0 mg m⁻² for the N+LS, N, and CK treatments, respectively. The promotion of N₂O production by highly available substrates confirms our hypothesis. Our work contributes to the refinement of global climate models and field mitigation practices, as pulsed N₂O emissions from croplands will increase under future extreme rainfall events owing to climate change.