# Monitoring soil greenhouse gas (GHG) emissions in a Sahelian agrosilvo-pastoral parkland

Seydina Mohamad Ba, Olivier Roupsard, Lydie Chapuis-Lardy, Frédéric Bouvery, Djim Mouhamadou Lamine Diongue, Yélognissè Frédi Agbohessou, Frédéric Guérin, Torbern Tagesson, Bienvenu Sambou, Dominique Serça

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## ► To cite this version:

Seydina Mohamad Ba, Olivier Roupsard, Lydie Chapuis-Lardy, Frédéric Bouvery, Djim Mouhamadou Lamine Diongue, et al.. Monitoring soil greenhouse gas (GHG) emissions in a Sahelian agrosilvo-pastoral parkland. EGU General Assembly 2022, May 2022, Vienne, Austria. 1 p., 10.5194/egusphere-egu22-4337. https://hal-05490285

HAL Id: hal-05490285

https://hal.science/hal-05490285v1

Submitted on 3 Feb 2026

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# Monitoring soil greenhouse gas (GHG) emissions in a Sahelian agrosilvopastoral parkland

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Seydina Mohamad Ba, Olivier Roupsard, Lydie Chapuis-Lardy, Frédéric Bouvery, Djim Mouhamadou Lamine Diongue, Yélognisse Frédi Agbohessou, Håkan Torbern Tagesson, Bienvenu Sambou, and Dominique Serça

https://doi.org/10.5194/egusphere-egu22-4337

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© Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License.

seydina1988@gmail.com
https://lped.info/wikiObsSN/?FaidherbiaFlux

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24 may 2022
- The impact of agrosilvopastoral systems in the Sahel on the carbon cycle and greenhouse gas (GHG) fluxes is very poorly documented

- Growing need to produce baseline data on GHG emissions

- Study of the temporal and spatial variability of GHG fluxes (between soil and atmosphere)

- Where?

- Agrosilvopastoral area dominated by the *Faidherbia albida*

- Cropped area (millet, groundnut in an annual rotation)

- Instrumented site (*Faidherbia* flux)

<figure><img src="image_6.png" /><figcaption>NIAKHAR (Sob) - Groundnut Bassin (SENEGAL)</figcaption></figure>

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Sources : Désignation : CRUA/EA, UNEP/DEWA, Arachide - SRD - A-LIFUR - AFDEC

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METHODS : Experimental design

**8 automatic chambers** used (**04 under trees** -Faidherbia albida- and **04 far from trees**)

With a groundnut plant during the rainy season and without a groundnut plant during the dry season

The whole is coupled to a **Picarro 5 gas analyser**

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© Design: F. Bouvéry

Photo credit: O. Roupsard

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Shaded chambers

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Full sun chambers

soil GHG analyser
shelter

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SN, Niakhar/Sob: Wet season

Photo credit: O. Roupsard
METHODS : in situ gas monitoring system (CO₂, CH₄, N₂O, H₂O and NH₃)

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https://www.youtube.com/watch?v=32VflJF4wug

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# Results : 8 months GHG fluxes (soil, plant and atmosphere)

## ☐ CO2 fluxes (measured from June 21 to January 22)

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DS = Dry season with bare soil

RS = Rainy season with cropped soil (groundnut)

* Soil respiration was highest after the first rainfall (high release of CO2 trapped in the soil pore spaces) and throughout the wet season.

* During the wet season, the maximum soil respiration at night was about 5 µmolCO2m-2s-1 and the maximum net CO2 uptake during the day was about -6µmolCO2m-2s-1

* Soil CO2 respiration was very low at the end of the dry season, with an average of about 0.6 µmolCO2m-2s-1.

* daily soil respiration is highest under trees (p< 0,0001), but the patterns remain similar
# Results : GHG fluxes exchange trends (soil, plant and atmosphere)

## Comparing soil fluxes to Eddy covariance (EC) measurements at 4.5 m above the crop

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DS = Dry season with bare soil

RS = Rainy season with cropped soil (groundnut)

* The CO2 fluxes from the automatic chambers show similar patterns to those from the EC tower.

* During the dry season, the CO2 fluxes obtained by automatic gas chambers were close to the EC fluxes. However, during the rainy season, with crop growth, a large difference was observed (i.e. a factor of 3.74 and 7 respectively for soil respiration and photosynthesis).

* This gap could be due to higher leaf cover in the field (as sensed by EC) as compared to leaf cover inside chambers.

* Therefore, we will soon apply correction per unit leaf area.
# Results : GHG fluxes exchange trends (soil, plant and atmosphere)

## ☐ H₂O, CH₄, N₂O and NH₃ fluxes trends

H₂O Flux (mmol H₂O m⁻² s⁻¹)

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NH₃ Flux (nanomol NH₃ m⁻² s⁻¹)

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LEGEND

▲ Shaded soil chambers_Avg

▲ Full sun soil chambers_Avg

— Rain (mm semih )

* No clear trend for the CH₄, N₂O, and NH₃ was found during the rainy season. The fluxes recorded look more like noise which decreases considerably in the dry season.

Another reason might be the low soil fertility, the lack of nitrogen supply, and the low moisture content in these sandy soils which are not suitable for trace gases production processes like N₂O and CH₄.

* H₂O fluxes seem to be more perceptible during the rainy season, possibly due to soil evaporation and plant transpiration, but with low intensity, as compared to EC fluxes (data not shown), probably due to vapor condensing in the pipes.
# Thank you

Looking forward to receiving any questions or comments

<figure><img src="image_21.png" /><figcaption>© Seydina Mohamad BA</figcaption></figure>

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https://lped.info/wikiObsSN/?Faidherbia-Flux

https://www.cassecs.org/

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https://www.youtube.com/watch?v=32VflJF4wug

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seydina1988@gmail.com
olivier.roupsard@cirad.fr

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