ABSTRACT:Restoration of atmospheric carbon in soils has principal many good effects. Arid lands cover more than 40 % of the global earth area, but only stock 16 % from the global carbon stock. It seems to be a suitable solution for this environmental issue, but still all variables controlling organic carbon in such kinds of soil, was ignored. This study aims to develop two models of organic carbon under clayey and sandy soils in semi-arid Mediterranean zones basing on physical and chemical soil properties. For establishing both models, structural equation modeling was used. For modeling organic carbon, two Tunisian soil databases composed from clayey and sandy soils made respectively, of 450 and 602 soil horizons were used. Using the two databases for all properties, the principal component analysis shows two components for clayey soil; (i) chemical properties and bulk density and (ii) physical properties. For the sandy soil it reveals two components; (i) chemical properties and (ii) physical properties. According to the derived components for each soil category, two models have been built. Structural equation modeling results show that clayey model has proved that organic carbon was controlled by chemical properties and bulk density more than physical properties and sandy model has proved that organic carbon was controlled by chemical properties more than physical properties. The root mean square errors of approximation were 0.079 and 0.050 for the clayey and sandy models, respectively. Then these two models were validated with two other databases from Tunisian dryland soils.

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Communication présentée au 24th DAAAM International Symposium on Intelligent Manufacturing and Automation, 23-26 October 2013, Zadar, Croatia.Soil organic carbon (SOC) is of big importance in the global carbon cycle. Distribution patterns of SOC in various regions of Tunisia constitute a baseline for studies on soil carbon changes. This paper presents Tunisian SOC stock calculated using soil profile descriptions defined by FAO/UNESCO classification, and the digital soil map 1:500 000. A soil database has been compiled, containing data from 5024 horizons and 1483 profiles. SOC stocks have been calculated for each profile by a classical method for a given depth, it consists of summing SOC stocks by layer determined as a product of bulk density (Db), organic carbon (OC) content, and layer thickness. Db values were calculated from pedotransfer functions when we have missing values. SOC stocks by profiles were calculated and linked by soil type to polygons of a digital soil map of Tunisia. In total, Tunisian SOC stocks are 1.006 Pg C in the 0 to 100 cm soil depth, and 0.405 Pg C in the upper layer 0-30 cm. The surface horizon (0 – 30 cm) stored 40% of the soil organic carbon stock. OC stocks were higher in Luvisols 71.6 and 159.2 t/ha in 0 – 30 and 0-100 cm soil depth, respectively. In Podzoluvisols there are 6.19 and 138.8 t/ha, but amounts are lower in Lithosols at 18.4 and 40.4 t/ha