Abstract: Sub-humid and semi-arid zones comprise a land area of about approximately 1/3 of Tunisia, good agricultural soils and major organic carbon storage are situated in this region. The objective of this study is to investigate the organic carbon distribution and stocks in soils of this region under different land uses by using different investigations: (1) The conversion from natural forest to agricultural land caused significant loss of Soil Organic Carbon (SOC) stock, it induces a decrease of SOC stock with 19.33 t C ha-1, (2) however, restoring forestry after conversion from agricultural ecosystems to forest, we found an increase of SOC stock with 0.42 t C/ha/year, (3) soil carbon sinks increase most rapidly under practice of no-tillage compared with conventional tillage, no-tillage treatment was found to increase the storage of OC in the surface layer 0-20 cm compared to conventional tillage and (4) irrigation with saline water stock higher than irrigation with freshwater only at superficial layer. Although, under this depth, irrigation with freshwater and at total profile stock higher than saline water. SOC stock is 148.5 t ha-1 in the freshwaters irrigated soils against 139.6 t ha-1 in saline water irrigated soil.