Gully erosion is one of the main processes of soil degradation, representing 50%–90% of total erosion at basin scales. Thus, its precise characterization has received growing attention in recent years. Geomatics techniques, mainly photogrammetry and LiDAR, can support the quantitative analysis of gully development. This paper deals with the application of these techniques using aerial photographs and airborne LiDAR data available from public database servers to identify and quantify gully erosion through a long period (1980–2016) in an area of 7.5 km² in olive groves. Several historical flights (1980, 1996, 2001, 2005, 2009, 2011, 2013 and 2016) were aligned in a common coordinate reference system with the LiDAR point cloud, and then, digital surface models (DSMs) and orthophotographs were obtained. Next, the analysis of the DSM of differences (DoDs) allowed the identification of gullies, the calculation of the affected areas as well as the estimation of height differences and volumes between models. These analyses result in an average depletion of 0.50 m and volume loss of 85000 m³ in the gully area, with some periods (2009–2011 and 2011–2013) showing rates of 10,000–20,000 m³/year (20–40 t/ha*year). The manual edition of DSMs in order to obtain digital elevation models (DTMs) in a detailed sector has facilitated an analysis of the influence of this operation on the erosion calculations, finding that it is not significant except in gully areas with a very steep shape.

In Tunisia, the olive is the most cultivated fruit crop in the northern region, where annual rainfall exceeds 400 mm. This olive-growing area is characterized by a wide coverage of marginal soil with a high slope gradient. Therefore, the inclusion of cover crops in olive orchards is a sustainable solution to enhance ecosystem productivity, improve soil fertility, and increase oil yields. This study aimed to investigate the short-term (two cropping seasons in 2021 and 2022) effects of different seeded cover crops and soil management practices on soil characteristics, as well as soil health by measuring soil enzyme activities and microbial diversity. Six cover crop types consisting of wheat, vetch, oat, fenugreek, a vetch–oat mixture, and spontaneous vegetation were tested in association with rainfed olive trees (cv. Chetoui) in the north of Tunisia and compared to a control (which was tilled periodically three times per year without intercropping). During the first cropping season, cover crops were cut as animal feed, and only residues were incorporated into the soil. However, during the second year, all cover crop biomass was incorporated into the soil. The results indicated that the dry biomass production and carbon uptake were significantly higher in grass species (wheat and oat). All of the cover crops, including the spontaneous vegetation, significantly increased soil organic matter (SOM) and macronutrient levels, mainly, available phosphorus. On the other hand, the highest level of soil nitrogen was found in the fenugreek cover crop. The soil enzyme activities in the cover crops of wheat, oat, and the vetch–oat mix were higher than those in the control. Together with the increase in soil organic matter (SOM), this demonstrates a significant improvement in soil health with cover crops. Furthermore, this study proves that the utilization of carbon sources was dominated by amides, amines, and amino acids in the fenugreek plot, while it was dominated by polymers and carboxylic acids in the case of the wheat and oat. Overall, this study demonstrates that seeding cover crops is a sustainable management practice not only to integrate livestock but also to improve soil health in semiarid olive orchards.

Cropland soils are key systems in global carbon budgets due to their high carbon-sequestration potential. It is widely accepted that clays are one of the soil components that have a significant effect on the stabilisation of soil organic carbon (SOC), owing to its surface interactions with organic molecules. However, the identification of the direct effects of clays on SOC stabilization is complicated, mainly due to the difficulty of accurately characterizing the mineralogy of clays, especially phyllosilicates. In this study, the relationships between soil phyllosilicates and functional SOC pools in woodlands and comparable olive groves, under two contrasting management systems (bare soils versus soil under cover crops) and parent materials (calcareous and siliceous), were explored. The total mineralogy of soil and clay fractions and the soil-clay assemblages were analysed through the decomposition of X-ray diffraction patterns, and were then related to four SOC pools. Total and unprotected SOC was higher in olive groves under cover crops, and this was true independent of the parent material, proving the importance of herbaceous covers in SOC sequestration in woody crops. Some significant correlations between clay minerals and SOC fractions were found. Interestingly, mixed-layer content was correlated with the biochemically protected SOC fraction (r = 0.810, p < 0.05), and this was so even when the partial correlation coefficient was calculated (r = 0.761, p < 0.05). According to the partial correlation networks (PCN), four separated clusters of variables were obtained, which joined into only one at fdr < 0.25. The PCNs supported the direct correlation between mixed-layer content, especially those rich in smectite, and the biochemically protected SOC fraction, suggesting that smectite layers may stabilize organic molecules. Since potassium enrichment is higher in the rooted layers of woodland and soils under cover crops, and this increase is related to the collapse of swelling layers, these soils were poorer in smectite phases than the bare soils. This also would explain why the biochemically protected SOC was more abundant in the latter.