Greenhouse gas production, diffusion and consumption is depth dependent

Mr Erik Button1, Prof Dave Chadwick1, Prof Davey Jones1,2

1School of Natural Sciences, Bangor University, Bangor, United Kingdom, 2UWA School of Agriculture and Environment, University of Western Australia, Crawley, Australia

Successfully meeting mitigation targets of climate agreements can be achieved with help of specific strategies, such as enhanced soil carbon (C) sequestration. While topsoils have been the major focus of sequestration research, subsoils have characteristics (e.g. old and stable C, low microbial activity, low disturbance) that offer substantial potential to sequester C. However, due to limited research, crucial aspects of subsoil C dynamics remain unknown.

For the development of effective sequestration methods, it is important to understand how the dynamics of greenhouse gases (GHGs), produced by soil organic matter mineralisation, differs throughout the soil profile. Few studies that research soil GHG dynamics venture below the soil surface and indeed none have monitored and experimentally tested GHG production, consumption and diffusion in a vertical soil profile.

In this 12-month study, we investigate the dynamics of nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂) in an arable soil by sampling from gas collectors inserted into a maize field at 10, 20, 30 and 50 cm depths. In addition, laboratory experiments were conducted to a) determine soil CO₂ production rates and N₂O and CH₄ consumption rates at different depths, and b) test how these GHGs diffuse through the soil profile using sterilised soil and a conservative tracer gas.

Our results from the field gas collectors show a significant increase in GHG concentrations with soil depth. Laboratory experiments suggest that the higher concentrations of GHGs observed in deeper soil layers are due to reduced gas diffusion, greater production of N₂O and CH₄ at depth and consumption of N₂O and CH₄ by microbial processes closer to the surface.

The dynamics of subsoil GHGs are crucial in determining C balances, and a soil’s ability to offset GHGs via long-term C sequestration in the subsoil.


Biography: I developed a keen interest in soil science during my undergraduate studies at the University of Sheffield, UK. I went on to study a Masters with Prof Jonathan Leake investigating how hedgerows may be harnessed to improve arable soil recovery. This strengthened my interest in soil and led me to study for a PhD in subsoil carbon dynamics at Bangor University, Wales, with Prof Davey Jones and Prof Dave Chadwick. I am fascinated by the understudied and unknown nature of deep soils and hope to shed some light on the carbon dynamics which are occurring in this soil zone.

SOIL ORGANIC MATTER

7th International Symposium
Soil Organic Matter

6 – 11 October 2019

Hilton Adelaide

Adelaide, South Australia

Australia

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