Soil Properties and Organic Carbon Stock of Soils under Arid Coastal Ecosystem Oasis in Southern East of Tunisia

Abstract—Our knowledge about soil properties and soil organic carbon stock under arid ecosystems is crucial if we are to optimize soil organic carbon sequestration to mitigate climate changes. This study aims at investigating soil properties, soil organic carbon (SOC) pools, and stocks in soil under arid ecosystem oasis. Soil samples were randomly collected from 0–5 and 0–30 cm depths in 17 sites (34 samples). The bulk density, pH, electrical conductivity EC, calcium carbonate and gypsum were measured in soil samples. Total SOC, particulate organic carbon (POC), SOC associated with the fine mineral fraction concentrations and stocks were also determined. Results showed that soils under oasis are characterized by high pH and EC values. Similarly we recorded great amount of CaCO₃ and gypsum among sites and depths. However bulk density values ranged from 1.23 to 1.30 and 1.18 to 1.35 g cm^–3 respectively in 0–5 and 0–30 cm layer depths. The total SOC concentrations range on average between 8.47 to 13.25 g kg^–1 and between 9.27 to 11.06 g kg^–1 in 0–5 and in 0–30 cm layers respectively. In all samples the SOCff represents the major organic pools of SOC (>60%). Among sites the SOCs in 0–5 cm layer depth were between 0.4 and 0.8 kg C m^–2 and reach 4 kg C m^–2 (40 t ha^–1) in 0–30 cm. The POCs constitute only between 21 and 34%. The correlation matrix established between soil properties shows significant negative correlation (p = 0.05) between POC and EC. However, SOCs are largely positively correlated (p = 0.01) with different SOC pools. It can be said that soils under oasis store relatively high amount of organic carbon. Therefore, this study confirms that arid soils can be considered as a potential sink in North Africa to sequester SOC.