Distribution of soil carbon according to pedological profile in the Sudanese savannah Agro-systems of Bondoukuy, western Burkina Faso

A study was conducted to examine the vertical distribution of soil organic carbon (SOC) in savannah agrosystems within the cotton farming region of Burkina Faso. The study was conducted on plots belonging to two village lands and two distinct morpho-pedological environments. The first area is characterised by a sandy flatland with light ferruginous soils and a low content of SOC. The second area is distinguished by a sandy-loam lowland with heavier soils and a high content of SOC. A total of 13 plots, comprising natural vegetation, crops or fallow land, were sampled along transects. The history of each plot, whether cultivated or in spontaneous vegetation, was obtained through surveys and field observations. The variability of the soil was addressed by the study of 13 profiles. The soil organic carbon (SOC) content was determined for each distinct horizon in the profiles, and a five-fraction granulometry was conducted on the composite horizon 0-20 cm in the 13 plots. The findings indicate that soil organic carbon (SOC) concentrations are higher in the lowland area than in the flatland area. The results demonstrate that the lowland area is characterised by a prevalence of hydromorphic tropical ferruginous soils, which exhibit elevated levels of carbon compared to ferruginous soils with iron sesquioxide and ferralitic soils in the flatland area. The content of fine elements serves to confirm the names of the two morpho-pedological environments. Furthermore, it elucidates the underlying causes of the observed variability in soil organic carbon (SOC) content, which is evident between the two environments. The other primary explanatory variables are soil type (i.e., moisture levels and waterlogging), vegetation type, and the use of the environment through cropping systems. It is notable that there are considerable fluctuations in carbon between the crop and fallow stages in these areas, although the variation is relatively low (+3%). Additionally, some plots with relatively high C content received substantial quantities of manure. The carbon content of the soil tends to decrease as a result of the specific cropping system and the way in which the land is used. As the predominant practice of farming since the 1950s has been shifting cultivation, and given that the land under permanent cultivation is the most clayey, the loss of soil organic carbon (SOC) following a change in land use is considerably less than that predicted by current models. In consideration of the dynamics of land use since 1950, it can be posited that a maximum of 3% of carbon in arable soils has undergone a slight reversible process of disappearance, occurring primarily in the 0-20 cm horizon and amounting to a mere 0.5t/ha. Nevertheless, this decline would have ceased (end of the labile C stock, maintenance of fallow cultivation on poor land) were it not for the possibility of increased tillage intensity.