Methane Flux from Non-flooded Soils

Methods 5.0

on-farm
non-mechanical
Annual methane flux from soils under predominantly aerobic conditions.
Published

September 22, 2025

Introduction

Methane flux in non-flooded soils is an addition for Fieldprint Platform version 5.0, using the method from Ogle et al. (2024). This represents a very minor source of GHG emissions or sequestration.

Annual methane (CH4) net uptake or emission (tonne CH4) from soils results from the balance of two processes: methanogenesis, which occurs under anaerobic conditions, and methanotrophy, which is the dominant process under aerobic conditions.

In non-flooded mineral soils (NFMS), aerobic conditions are predominant and net uptake or negative fluxes of CH4 are expected.

Using closed-vented chambers, biological science aide Rochelle Jansen (right) and soil scientist Jane Johnson collect gas emissions from soil at a research farm. Samples will be analyzed for carbon dioxide, nitrous oxide, and methane. Photo by Stephen Ausmus. USDA ARS.

Using closed-vented chambers, biological science aide Rochelle Jansen (right) and soil scientist Jane Johnson collect gas emissions from soil at a research farm. Samples will be analyzed for carbon dioxide, nitrous oxide, and methane. Photo by Stephen Ausmus. USDA ARS.

Methods

The rate of uptake will depend on the land use. For these situations, the annual CH4 flux is determined by the average CH4 uptake in soils with natural vegetation (\([CH_4]^{base}\)) and a multiplying factor related to the current land use (\(MF\)) as follows:

\[ [CH_4]^{total} = [CH_4]^{base} \times MF \times A \times 10^3 \]

  • \([CH_4]^{total}\) = the annual total CH4 flux (kg CH4)
  • \(A\) = the area of the land parcel (ha)
  • \([CH_4]^{base}\) = the base annual CH4 flux per area for mineral soils with natural vegetation (tonne CH4 ha-1)
  • \(MF\) = the management factor for cropland and grazing land NFMS (dimensionless)

The methane flux per area and per crop production unit can be estimated with the following equations:

Emissions per area and per crop production unit

Provided the area and crop yield, the annual total CH4 emissions can be computed per area and per crop production unit as follows:

\[ \begin{align} [CH_4]^{area} &= [CH_4]^{total} \times A^{-1} \\ [CH_4]^{prod} &= [CH_4]^{total} \times (A \times Y)^{-1} \end{align} \]

where:

  • \([CH_4]^{area}\) = the annual total CH4 flux per area (kg CH4 ha-1)
  • \([CH_4]^{prod}\) = the annual total CH4 flux per crop production unit (kg CH4 [crop prod unit]-1)
  • \(A\) = the area of the land parcel (ha)
  • \(Y\) = the crop yield (crop production units ha-1)

Conversion CH4 to CO2e

Finally, methane flux can be expressed as CO2e as follows:

\[ \begin{align} [CO_2\text{e}]^{total} &= [CH_4]^{total} \times [CH_4]^{gwp} \\ [CO_2\text{e}]^{area} &= [CH_4]^{area} \times [CH_4]^{gwp} \\ [CO_2\text{e}]^{prod} &= [CH_4]^{prod} \times [CH_4]^{gwp} \end{align} \]

where:

  • \([CO_2\text{e}]^{total}\) = the annual total CO2e flux (kg CO2e)
  • \([CO_2\text{e}]^{area}\) = the annual total CO2e flux per area (kg CO2e ha -1)
  • \([CO_2\text{e}]^{prod}\) = the annual total CO2e flux per crop production unit (kg CO2e [crop production units]-1)
  • \([CH_4]^{gwp}\) = the global warming potential factor for CH4 (kg CO2e / kg CH4)

References

Ogle, Stephen M, Paul R Adler, Gary Bentrup, Justin Derner, Grant Domke, Stephen Del Grosso, Johannes Lehmann, Michele Reba, and Dominic Woolf. 2024. “Chapter 3: Quantifying Greenhouse Gas Sources and Sinks in Cropland and Grazing Land Systems.” In: Hanson, Wes L.; Itle, Cortney; Edquist, Kara, Eds. Quantifying Greenhouse Gas Fluxes in Agriculture and Forestry: Methods for Entity-Scale Inventory. Technical Bulletin Number 1939, 2nd Edition. Washington, DC: US Department of Agriculture, Office of the Chief Economist. 6-1-6-23. Chapter 3. 1939: 31.