Organic Matter Quality and Clay Mineral Type of Soils on a Catena in Deilaman Region of Guilan Province

This research is conducted to evaluate the quality of organic matter and clay type in the soils which are located at different positions of the slope of a catena in Deilaman region of Guilan province. To do this, the catena was firstly divided into five transverse sections including summit, shoulder, back slope, foot slope and toe slope. Then each section was longitudinally divided into three parts as three replications and composite soil samples were collected from each sections at the depths of 0-20, 20-40 and 40-60cm and some characteristics of soils and clay minerals of the samples were determined. Results showed that the maximum organic matter and carbohydrate contents were found in the soils located on the lower positions of the catena (representing foot slope and toe slope). Carbon-nitrogen ratio decreased by reducing the slope, indicating the more decay of organic matter in the positions of foot slope and toe slope. Soil microbial respiration amounts also more increased with reducing of the slope. Clay mineralogy of soils located on the catena confirmed the presence of kaolinite, illite, hydroxy interlayer vermiculite and little amounts of chlorite in the soils. The type of clay minerals was the same but their frequency was varied at the different slope positions and soil depths. The results of present study revealed that soil properties were affected by topography in this region.