Short and Long-Term Effect of Land Use and Management on Soil Organic Carbon Stock in Semi-Desert Areas of North Africa-Tunisia

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

Carbon and nitrogen balances and CO2 emission after exogenous organic matter application in arid soil

Addition of organic amendments (OAs) could be a means to sequester carbon (C) in soils. However, the efficiency of C sequestration depends on how OAs evolve in the soil. A field study was installed in arid soil to which was added one of five OAs – olive husk-based compost (CM), palm leaf-based compost (CP), crushed olive pruning (GW), fresh olive mill wastewater (OMW) or fermented ovine manure (OM) – at an equivalent fixed level of 350 g of C/m2. C and N mineralization were followed for 112 days by measuring the evolution of released CO2 and mineral N evolution. The results showed that CM and CP did not disturb soil respiration, with a very low CO2 emission or almost no respiration for the CM, while CO2 release reached 7.6 g of CO2/m2 for GW and OMW. Soil organic carbon (SOC) was sustainably improved by 0.54% and 0.50%, respectively, for CM and CP. N mineralization showed no significant difference between amended and untreated soils. Based on these results, compost amendment was the most efficient for C sequestration to enhance soil fertility and consequently reduce the rate of CO2 emission