A Review of the Movement and Fate of N2O in the Subsoil

Abstract

Understanding the fate of N 2 O in the subsoil is important in accurately assessing the direct and indirect fluxes of N 2 O to the environment. The production, movement and ultimate fate of N 2 O in the subsoil are all poorly understood. Movement of N 2 O in the subsoil occurs predominantly via diffusion but convective fluxes can also occur. Diffusion gradients in the soil have been used to determine N 2 O surface fluxes with varying success. Infiltration of water into the soil may lead to entrapment, and the temporary storage of N 2 O, ebullition, or the transport of dissolved N 2 O in soil leachates. The reduction of N 2 O to N 2 is potentially enhanced when N 2 O is entrapped. Few studies have examined the effect of infiltrating water on a previously known N 2 O concentration in the soil. Future studies are required to better establish the consumption and movement of N 2 O in the subsoil during water infiltration. This paper reviews past work on the movement and fate of N 2 O in the subsoil and makes suggestions for future studies.

The fate of N<sub>2</sub>O consumed in soils

“…1): (1) complete denitrification to N 2 within the cell prior to its escape into the gas phase (reviewed in Zumft, 1997); (2) escape from the cell into the gas phase of soil and potentially to the atmosphere; or (3) complete denitrification to N 2 upon re-entering a cell capable to reduce N 2 O (e.g. Neftel et al, 2000;Clough et al, 2005). To the best of our knowledge other pathways have not been considered in natural soil so far.…”

An Initial Investigation into the Use of a Flux Chamber Technique to Measure Soil-Atmosphere Gas Exchanges from Application of Biosolids to UK Soils

“…By measuring N 2 O fluxes at the surface simultaneously with concentration in soil cores to a depth of approximately 10cm, moisture content was shown to cause a significant delay between production of N 2 O in the subsoil and flux measurements at the soil surface. Soil disturbances, especially agricultural practices, can release the trapped gas, for example, say [38] measured N 2 O fluxes of 9-31% above background concentrations 1 minute after cultivation, but these had reduced to background fluxes within 2 hours. It is also possible the gas will have dissolved and leached away to be emitted elsewhere or taken up by plants and transpired.…”

“…It is also possible the gas will have dissolved and leached away to be emitted elsewhere or taken up by plants and transpired. A more thorough understanding of the diffusion of gases formed in the subsoil is therefore also important [38]. Changes in ambient pressure and temperature have also been investigated and shown to lead to movement of gases in soils.…”

“…Studies have measured N 2 O concentration in soil leachates but have not correlated these with concentrations in the soil profile. Readily available C has been identified as a limiting factor for this process [38], but studies have indicated that moisture content has a greater influence than C or N concentration.…”

Use of Artificial Neural Networks in Predicting Direct Nitrous Oxide Emissions from Agricultural Soils

“…Direct emission sources include: the use of nitrogen fertilizers, organic nitrogen emissions in animal faeces, land management and storage of sewage sludge. Indirect emissions come mainly from the evaporation of precipitation, surface runoff and leaching of nitrogen into groundwater and surface water [9,10]. N 2 O emissions from agricultural production has the main source in soil fertilized by mineral and organic fertilizers [11,12].…”