Effect of rewetting following drought on nitrous oxide and carbon dioxide emissions from temperate agricultural soils: the response to nitrogen is mediated by carbon availability

Background/Question/Methods

Soil drying and rewetting cycles will become increasingly important processes in temperate ecosystems with intensification of the water cycle due to climatic change. Understanding the effect of rewetting on soil greenhouse gases (GHG) emissions in agricultural ecosystems is especially essential since agriculture is a major land-use. In addition, understanding the controls on soil GHG emissions after rewetting is important for both biogeochemical modeling and carbon and nitrogen budgets calculations. We took advantage of the 2012 drought to investigate the effect of rewetting on soil GHG emissions in two fields under intensive agricultural management but with different land-use histories, and compared them to unmanaged grassland. We measured soil N₂O and CO₂ fluxes with static chambers via two analytical techniques — laboratory analysis using gas chromatography versus an in situ analysis using a newly developed quantum laser coupled with an infra-red gas analyzer.

Results/Conclusions

Under drought conditions, average N₂O fluxes ranged between 2 and 12 g N ha^-1 d^-1 and were not affected by fertilization. After an artificial rain event of 50 mm, soil N₂O fluxes increased up to ~30 fold and were associated with both soil carbon availability and fertilization. Soil CO₂ emissions followed soil carbon availability and were 15, 28, and 45 kg C ha^-1 d^-1 for the two agricultural systems and the grassland ecosystem, respectively, and increased 1.4 – 2 fold after the artificial rain event. Under dry conditions water availability controlled soil GHG emissions. While the overall N₂O fluxes were associated with fertilization, the magnitude of the fluxes was associated with carbon availability. In contrast, soil CO₂ emissions were associated with water and carbon availability only. Results from the two analytical techniques were highly correlated and could be used interchangeably.