Impacts of land use and topography on soil organic carbon in a Mediterranean landscape (north-western Tunisia)

This study evaluates the impact of land use and topographic features (slope and aspect) on soil or-ganic carbon (SOC) within the Wadi Beja watershed in north-western Tunisia. A soil spectral library was set upto 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-facingareas 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, whichwere inter-planted with field crops, the slope significantly affected SOC content, which improved to 0.97 % inflat 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 af-fected 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 significanteffect on SOC content, which was higher in flat areas (north-facing: 1.15 %, south-facing: 1.14 %) than in steepareas (1.09 % in north-facing areas and 1.07 % in south-facing areas). This study highlights the ability of visibleand near-infrared (VNIR) spectroscopy to quantify C in diverse soils collected over a large diverse geographicarea in order to indicate that calibrations are feasible, and therefore, assessing the variation of SOC content underland use and topographic features (slope and aspect) will result in better sustainable land management planning.