Abstract: A total of 325 samples collected from cultivated land profiles were analyzed to investigate the factors affecting soil organic matter (SOM) variability in different horizons (0-20 cm, 20-40 cm, and 40-60 cm). Factors including parent materials, land types, and elevation were examined by classical statistics and classification and regression trees (CART). The results showed that the CART models could explain 57%, 44%, and 35% variability of SOM in 0-20 cm, 20-40 cm, and 40-60 cm, respectively. SOM decreased with the increase of soil depth. More specifically, the mean value of SOM in the 0-20 cm soil horizon was 1.5 times higher than that in the 20-40 cm, and 2 times higher than that in the 40-60 cm. The factors affecting SOM variability differed with soil horizons. The most important parameters were parent material, land type, and elevation for 0-20 cm. Elevation was the critical variable for 20-40 cm and parent material was the key one for 40-60 cm. The interaction between elevation and parent material had a significant effect on the variation of SOM in different horizons. Soils developed from alluvial and limestone parent material had higher values of SOM content at an elevation range of 500-1 000 m. Elevation was positively significantly correlated with SOM in soils developed from purple parent material.