Effect of slope position and aspect on some physical and chemical soil characteristics in a loess hillslope of Toshan area, Golestan Province, Iran

Considering the importance of soil in supplying food for the increasing human population, knowledge of soil quality, including physical, chemical, biological and mineralogical properties are important. Spatial variability of soil properties is related to environmental factors such as climate, slope position, topography, slope gradient, elevation, parent material and vegetation. Topography variability and soil formation cause the significant differences in soil characteristics in a hillslope. The main objective of the present study was to assess some physical, chemical and biological indicators of soil quality in a loess hillslope of Toshan area in Golestan Province, Northen Iran. Therefore 135 samples were collected at random systematic method (0-20 cm depth) at three aspects and four slope positions. Soil texture, bulk density, organic carbon (OC), electrical conductivity, pH, microbial respiration rate, calcium carbonate equivalent (CCE) and mean weight diameter (MWD) of aggregates were measured for studying soil quality, including physical, chemical and biological. The results indicated that the lower slope positions had the highest amounts of clay, OC, MWD and the lowest CCE and soils in north-east aspect had higher OC compared to other aspects. Therefore, it is concluded that most soil properties are dependant largely on slope position and aspect that could have a long-term influence on soil development and evolution. Among the soil properties, OC is a suitable indicator for assessing the effects of slope position and aspect on soil quality in the studied area.