Soil organic carbon (SOC) is one of the most important carbon stocks and has large potential to affect global climate. Management of soils to increase SOC levels can therefore increase the productivity and sustainability of agricultural systems and provide a framework to control land degradation and also for identification of sustainable management. The aspect and slope can control the movement of water and material in a hillslope and contribute to the spatial differences of soil properties. The aim of this study is to characterize spatial patterns of the concentrations of topsoil SOC on different slope aspects in a loess hillslope of Toshan area in Golestan Province, Northen Iran. Therefore, 96 soil samples were collected at three aspects (north-east (NE), east (E) and south-east (SE)) in a hillslope with cultivated landuse. SOC was measured for the collected soil samples. Slope and aspect attributes were calculated by a digital elevation model using ArcGIS 9.3. The results of ANOVA showed that mean, minimum and maximum of SOC in north-east (NE) is more than other aspects and showed significant differences (P < 0.05) compared to the other aspects. It is therefore concluded that accumulation of topsoil SOC is dependent on aspects at the local-scale and it seems that areas on the east and south-east facing slopes are the most sensitive areas for agriculture which need protecting and control measures.

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