Challenges of soil carbon sequestration in the NENA region

摘要

Abstract. The Near East North Africa (NENA) region spans over 14 % of the total surface of the Earth andhosts 10 % of its population. Soils of the NENA region are mostly highly vulnerable to degradation, and futurefood security will much depend on sustainable agricultural measures. Weather variability, drought and depletingvegetation are dominant causes of the decline in soil organic carbon (SOC). In this work the status of SOC wasstudied, using a land capability model and soil mapping. The land capability model showed that most NENAcountries and territories (17 out of 20) suffer from low productive lands (> 80 %). Stocks of SOC were mapped(1 V 5000000) in topsoils (0–0.30 m) and subsoils (0.30–1 m). The maps showed that 69 % of soil resources areshown to have a stock of SOC below the threshold of 30 tons ha?1. The stocks varied between ≈ 10 tons ha?1 inshrublands and 60 tons ha?1 for evergreen forests. Highest stocks were found in forests, irrigated crops, mixedorchards and saline flooded vegetation. The stocks of soil inorganic carbon (SIC) were higher than those of SOC.In subsoils, the SIC ranged between 25 and 450 tons ha?1, against 20 to 45 tons ha?1 for SOC. Results highlightthe contribution of the NENA region to global SOC stock in the topsoil (4.1 %). The paper also discusses agricultural practices that are favorable to carbon sequestration such as organic amendment, no till or minimum tillage,crop rotation and mulching and the constraints caused by geomorphological and climatic conditions. The effectsof crop rotations on SOC are related to the amounts of above and belowground biomass produced and retained inthe system. Some knowledge gaps exist, especially in aspects related to the impact of climate change and effectof irrigation on SOC, and on SIC at the level of the soil profile and soil landscape. Still, major constraints facingsoil carbon sequestration are policy-relevant and socioeconomic in nature, rather than scientific.