Does agricultural practices impact the quantity and the forms of organic carbon stored in cultivated soils of the Senegal groundnut basin ? : a rock-eval approach [résumé]

Soil organic carbon (SOC) is a key element in the functioning of agrosystems. It ensures soil quality and productivity of cultivated systems in the Sahelian region. This study uses Rock-Eval pyrolysis to examine how cultural practices impact SOC quantity and quality of cultivated sandy soils in the Senegal groundnut basin. Such thermal analysis method provides cost-effective information on SOC thermal stability that has been shown to be qualitatively related to SOC biogeochemical stability. Soils were sampled within 2 villages agricultural plots representative of local agricultural systems and for local preserved areas. Total SOC concentrations ranged from 1.8 to 18.5 g.kg-1 soil (mean ± standard deviation: 5.6 ± 0.4 g.kg-1 soil) in the surface layer (0-10 cm) and from 1.5 to 11.3 g.kg-1 soil (mean ± standard deviation: 3.3 ± 0.2 g.kg-1 soil) in 10-30 cm deep layer. SOC of cultivated soils significantly (p-value +manure > +millet residues > no input. Our results show that the quantity and the quality of SOC are linked to each other and both depend on land-use and agricultural practices, especially the nature of organic inputs. This correlation is very strong in the tree plantation (R² = 0.98) and in the protected shrubby savanna (R² = 0.97). It remains important for cultivated soils receiving organic wastes (R² = 0.82), manure (R² > 0.75), or millet residues (R2 = 0.91) but it's no more significant in no-input situations. The Rock-Eval based indexes were depicted in a I/R diagram that illustrate the level of SOC stabilization and plotted against comparable results from literature. The Senegalese sandy soils have thermal signatures showing an inversion of the I and the R indexes compared to data from the literature and highlighting SOC stabilization as a function of soil depth. Indeed, the studied soils were characterized by a more abundant refractory pool (A5 which ranged from 7.7 to 21.3 % in 0-10 cm layer and from 12.5 to 24.3 % in 10-30 cm, respectively) compared to other tropical soils. The SOC in these sandy soils while positively affected by organic inputs is dominated by labile forms that mineralize quickly which is excellent for the needs of productivity of these agrosystems but not for mitigation of climate change

Is the thermal stability of soil organic matter related to its biogeochemical stability in cultivated Arenosols of the groundnut basin of Senegal ? [résumé]

EGU.European Geosciences Union General Assembly, en ligne, , 19-/04/2021 - 30/04/2021Soil carbon (C), now more than ever, attracts the interest of the scientific community for its importance in combating climate change and achieving food security. As a result, its key role in agricultural soil fertility and in anthropogenic greenhouse gas emissions mitigation is high on international agendas. A key issue regarding the linkage between food security and carbon storage concerns the mineralization or the stability of soil organic matter (SOM). Rock-Eval® analysis was used to examine the thermal stability of SOM and these results were presented in details at the EGU General Assembly in 2020 (EGU2020-11229). Several indicators are used to further appreciate the quantity and quality of SOM: particle size fractionation (POM-C), determination of permanganate oxidizable carbon (POX-C) and carbon mineralization kinetics (Min-C). The results of both approaches are crossed and presented here. Soils were sampled from two soil layers (0-10 et 10-30 cm) in agricultural plots representative organic inputs practices in local agricultural systems (No input, +Millet residues, +Manure and +Organic wastes). Total soil organic carbon (SOC) concentrations ranged from 1.8 to 18.5 g C.kg-1 soil (mean ± standard deviation: 5.6 ± 0.4 g C.kg-1 soil) in the surface layer (0-10 cm) and from 1.5 to 11.3 g C.kg-1 soil (mean ± standard deviation: 3.3 ± 0.2 g C.kg-1 soil) in 10-30 cm deep layer. The soil organic matter in these Arenosols while positively affected by organic inputs is dominated by thermally labile forms. The POM-C fractions represent respectively 45 % and 24 % of the COS in the 0-10 cm and 10-30 cm soil layers respectively. Permanganate oxidizable carbon (POX-C) and mineralizable C (Min-C) averaged 254 ± 14 mg C.kg-1 soil and 10.7 ± 1.2 mg C-CO2 kg-1 soil in the 0-10 cm layer. Our results show that in different situations, the labile pools POM-C, POX-C and Min-C are linked to the active thermal pools A1 (highly labile pool), A2 (labile pool), A3 (resistant pool) and even A4 (refractory pool). The A3 and A4 pools, which are known to be relatively stable in more clayey soils, are in fact quickly mineralized in the sandy soils of this region. This intense mineralization of SOM promotes the recycling of nutrients which is excellent for productivity of these agrosystems, but not for mitigation of climate change in the long term

Agroecological transformation for sustainable food systems : Insight on France-CGIAR research

This 26th dossier d’Agropolis is devoted to research and partnerships in agroecology. The French Commission for International Agricultural Research (CRAI) and Agropolis International, on behalf of CIRAD, INRAE and IRD and in partnership with CGIAR, has produced this new issue in the ‘Les dossiers d’Agropolis international’ series devoted to agroecology. This publication has been produced within the framework of the Action Plan signed by CGIAR and the French government on February 4th 2021 to strengthen French collaboration with CGIAR, where agroecology is highlighted as one of the three key priorities (alongside climate change, nutrition and food systems)