Challenges of soil carbon sequestration in NENA Region

Abstract. North East North Africa (NENA) region spans over 14 % of the total surface of the Earth and hosts 10 % of its population. Soils of the NENA region are mostly highly vulnerable to degradation, and food security will depend much on sustainable agricultural measures. Weather variability, drought and depleting vegetation are dominant causes of the decline in soil organic carbon (SOC). In this work the situation of SOC was studied, using a land capability model and soil mapping. The land capability model showed that most NENA countries (17 out of 20), suffer from low productive lands (> 80 %). Stocks of SOC were mapped (1 : 5 Million) in topsoils (0–30 cm) and subsoils (30–100 cm). The maps showed that 69 % of soil resources present a stock of SOC below the threshold of 30 t ha−1. The stocks varied between ≈ 10 t ha−1 in shrublands and 60 t ha−1 for evergreen forests. Highest stocks were found in forests, irrigated crops, mixed orchards and saline flooded vegetation. The stocks of SIC were higher than those of SOC. In subsoils, the SIC ranged between 25 and 450 t ha−1, against 20 to 45 t ha−1 for SOC. This paper also highlights the modest contribution of NENA region to global SOC stock in the topsoil not exceeding 4.1 %. The paper also discusses agricultural practices that are favorable to carbon sequestration. Practices of conservation agriculture could be effective, as the presence of soil cover reduces the evaporation, water and wind erosions. Further, the introduction of legumes, as part of a cereal-legume rotation, and the application of nitrogen fertilizers to the cereal, caused a notable increase of SOC after 10 years. The effects of crop rotations on SOC are related to the amounts of above and belowground biomass produced and retained in the system. Some knowledge gaps exist especially in aspects related to the effect of irrigation on SOC, and on SIC at the level of soil profile and soil landscape. Still, major constraints facing soil carbon sequestration are policy relevant and socio-economic in nature, rather than scientific.