No 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 southfacing). 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.

Abstract. This study evaluated the impact of land use and landscape forms on SOC within the Wadi Beja watershed in north-western Tunisia. A soil spectral library was set to assess the variation of the SOC of 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, which SOC levels in north-facing areas appear higher in flat areas (0.75 %) than in hilly areas (0.51%). However, in south-facing areas, SOC levels were also higher in flat areas (0.74 %) than in hilly areas (0.50 %). For permanent crops, which was interplanted with field crops, the slope significantly affected SOC levels where SOC levels have been improved to 0.97 % in flat north facing and 0.96 % in flat south-facing areas, which are higher than hilly south – and north-facing areas (0.79 %). In the grazing land use system, both investigated factors – aspect and slope – significantly affected the SOC levels which, SOC levels were significantly higher in flat areas (north-facing: 0.84 %, south-facing: 0.77 %), compared to hilly areas (north-facing: 0.61 %, south-facing: 0.56 %). For the forest, none of the factors had a significant effect on the SOC, which they are higher in flat areas (north-facing: 1.15 %, south-facing: 1.14 %), compared to 1.09 % in north and 1.07 % in south-facing in steep areas. This study highlights the importance of the land use and landscape forms in determining the variation in SOC levels.