Abstract
Abstract. This study evaluates the impact of land use and topographic features (slope and aspect) on soil organic carbon (SOC) within the Wadi Beja watershed in north-western Tunisia. A soil spectral library was set up to assess the variation in the SOC for 1440 soil samples from four land use types (field crops, permanent crops, forest, and grazing land), three slope categories (flat, moderate, and steep) and two aspects (north- and south-facing). For field crops, only one factor – slope – significantly affected SOC, with SOC content in north-facing areas appearing to be higher in flat areas (0.75 %) than in hilly areas (0.51 %). However, in south-facing areas, SOC content was also higher in flat areas (0.74 %) than in hilly areas (0.50 %). For permanent crops, which were inter-planted with field crops, the slope significantly affected SOC content, which improved to 0.97 % in flat north-facing and 0.96 % in flat south-facing areas, scoring higher than hilly south- and north-facing areas (0.79 %). In the grazing land use system, both of the investigated factors – aspect and slope – significantly affected the SOC content, which was significantly higher in flat areas (north-facing: 0.84 %, south-facing: 0.77 %) than in hilly areas (north-facing: 0.61 %, south-facing: 0.56 %). For the forest, none of the factors had a significant effect on SOC content, which was higher in flat areas (north-facing: 1.15 %, south-facing: 1.14 %) than in steep areas (1.09 % in north-facing areas and 1.07 % in south-facing areas). This study highlights the ability of visible and near-infrared (VNIR) spectroscopy to quantify C in diverse soils collected over a large diverse geographic area in order to indicate that calibrations are feasible, and therefore, assessing the variation of SOC content under land use and topographic features (slope and aspect) will result in better sustainable land management planning.
Highlights
Land degradation is a major challenge for Mediterranean arid and semi-arid ecosystems (Hill et al, 2008)
A land use system (LUS) is defined as a sequence of goods and services obtained from land, but can involve particular management interventions undertaken by the land users as well
This study investigated four land use systems – field crops, permanent crops, forest plantation, and grazing land – in order to assess their effects on the variation of soil organic carbon (SOC) (Table 1)
Summary
Land degradation is a major challenge for Mediterranean arid and semi-arid ecosystems (Hill et al, 2008). In Tunisia, human activities are responsible for land degradation through deforestation, overgrazing, removal of natural vegetation, and agricultural practices that exacerbate soil erosion (Sarraf et al, 2004). Soil degradation processes include biological degradation (e.g. soil fertility and soil fauna decline), physical degradation (e.g. compaction, soil erosion, and waterlogging), and chemical degradation (e.g. acidification nutrient and depletion), which are mostly caused by agricultural practices (Diodato and Ceccarelli, 2004; Post and Kwon, 2000). There are both natural and human-induced causes of soil degradation (Bhattacharyya et al, 2015)
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