The application of organic amendments is an important technique used to enhance carbon storage in soils, thereby reducing CO2 emissions and mitigating climate change. The role of the composition of organic amendment in CO2 emissions is not well understood, however. The aim of this study was to understand the effect of the biochemical composition of organic amendments on CO2 emission and carbon stabilization. To do this, the application to the soil of five organic amendments with different biochemical compositions was considered. The effects of two types of compost (CH and CP), green manure (GM), olive mill waste water (OMW) and manure (M) on the rate of mineralization and humification of organic carbon were studied under controlled conditions. A single dose of 350 mg of organic carbon/100 g of soil was tested. These treatments, and the control soil, were incubated for 56 days. Soil respiration, organic carbon evolution, and the polymerization index were measured during the incubation period. The results showed that CO2 emission was strongly associated with the soluble fraction and the lignin content. Olive mill water, with the highest soluble fraction, induced the highest rate of mineralization. Composts CH and CP, with the greatest lignin content, were the most resistant to short‐term decomposition, and permitted the highest amount of carbon to be stored in the soil. Overall, this study showed that composts were the best form of organic C application. Indeed, with the composts, low direct mineralization was detected, improving the humidification processes and resulting in enhanced C storage in the soil. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

Soil organic carbon (SOC) plays an important role in the global C cycle, as well as in the maintenance and improvement of the soil quality. Over time, special attention has been paid to it in the study of the SOC reserves worldwide; however, reduced attention has been given to assessing the spatial patterns of SOC stock (SOCS) in semi-desert ecosystems. In this line, there are no conclusive studies in drylands of Africa affected by aeolian processes (semi-desert conditions) mainly due to the complexity of sample collection, and this is especially significant in some soil types such as Arenosols (AR) and Calcisols (CL). This study evaluated the spatial variability of SOC and SOCS in AR and CL with woody crops in relation to land use and management (old plantations > 100 years: centenary olive grove; new plantations < 12 years: young olive grove, almond, and pistachio) in semi-desert conditions. For this purpose, 16 soil profiles (for 0–40 and 40–100 cm depth) were selected and studied in an experimental area of Menzel Chaker-Sfax in southeastern Tunisia (North Africa). The main results indicated that the SOCS on average was higher in Old Cultivated AR (OC-AR) with 41.16 Mg ha−1 compared to Newly Cultivated AR (NC-AR) with 25.13 Mg ha−1. However, the SOCS decreased after a long period of cultivation in CL from 43.00 Mg ha−1 (Newly Cultivated CL: NC-CL) to 32.19 Mg ha−1 (Old Cultivated CL: OC-CL). This indicates that in the long term, CL has more capacity to store SOC than AR, and that in the short term, AR is more sensitive to land management than CL.