Soil Carbon Stocks Evolution in Organic Cotton-Based Cropping Systems in Southern and Northern Sudanese Agro-Ecological Zones of Burkina Faso

Variation of soil carbon stock in the cropping systems is an important indicator of their sustainability. The present study was conducted in 2015 and 2018 in seven organic cotton production areas distributed over the Southern and Northern Sudan agro-ecological zones in Burkina Faso. Soil samples were collected in 2015 as baseline and in 2018, after three years of cropping seasons, to determine the variations in carbon stocks in plots under organic farming systems. Surveys were also conducted to understand the fertilization practices implemented by producers during the same period. The results revealed that the recommended fertilization packages were not respected due to low production capacity and under using of organic manure. After three years of cropping in 2018, the deficit of organic restitution has led to a high decline of the soil carbon stocks. This decline was more severe in the 0-10 cm depth in some soils where the decrease in carbon stocks ranged from -4.6 t/ha to -5.5 t/ha. The correlation between soil types and their carbon stocks in the 0-10 cm soil layer was found to be significant (p < 0.05) in the Northern Sudan agro-ecological zone with adjusted R² = 74% and 54% in 2015 and 2018, respectively, and adjusted R² = 56% (2015) and 44% (2018) in the Southern Sudan agro-ecological zone. After three years of organic cotton-based farming, a decrease in the correlation between soil types and their carbon content was observed in the majority of cases. These results show that the process of carbon storage in soil is more influenced by agricultural practices and agro-ecological conditions than by the soil type.