Soil organic carbon stock in arid and semi-arid steppe rangelands of North Africa

The assessment of soil organic carbon stock (SOCS) in degraded and rehabilitated soils in steppelands and rangelands of North Africa is crucial for the adoption of adequate management strategies that respond to sustainable development. This study aimed to estimate the SOCS in the surface layer of soils rehabilitated by prickly pear plantations (PPP) and analyze the effects of edaphic factors controlling the variation of SOCS in old PPP (OPPP), young PPP (YPPP) and control plots (unplanted plots). Under arid and semi-arid climates, three steppe sites were sampled in which three plots with OPPP (age = 10-20 years), YPPP (age < 5 years) and controls plots were considered. In each plot, five quadrats were delimited and within each quadrat, two pedological profiles were dug to collect soil samples. The determined parameters were soil organic carbon (SOC), bulk density (BD), pH, electrical conductivity (EC) and total calcium carbonate. The averages of SOCS varied between 14.51 +/- 11.03 t/ha (min-max: 0.09-35.88 t/ha) under arid climate and 17.32 +/- 9.05 t/ha (range: 0.26-41.84 t/ha) under semi-arid climate. The variations of SOCS were significant (P = 0.002) between the type of steppe managements but not significant (P > 0.05) among climate zones. Generally, the control plots and OPPP stored more carbon (14-19 t/ha) than steppes with YPPP (11-14 t/ha). SOCS varied significantly with changes in soil depths, it reached 27 t/ha at 15 cm and dropped to 10-18 t/ha at 20 cm. Regardless of the type of climate and rangeland management, SOCS evolved with BD and soil organic matter. This study estimated for the first time the SOCS in soils of degraded steppe rangelands in North Africa. Even if the SOCS remains low degraded steppes rangelands, it is necessary to avoid the loss of SOC in these ecosystems. The adoption of conservation agricultural practices, e.g. organic matter addition and reduced tillage techniques can increase SOC levels in these ecosystems.