Variability of Particle Size Distribution in North and South Hillslopes in A Semi-Arid Region in West of Zanjan

Soil erosion by water is one of the most important destructive factors on the earth's surface. The slope and aspect are the factors controlling the movement of water and sediments on the surface of the slopes and have a special contribution in different soil characteristics. In general, the public relations of surface erosion and soil loss are continuous, depending on the degree and length of the slope. As the degree and length of the slope increases, the discharge and flow rate increases, and the rate of separation and transfer of particles increases as well. This study was conducted to investigate the effects of slope and aspect on soil characteristics in slopes with weak vegetation cover in Western Zanjan semi-arid region, northwest Iran. Five plateaus were surveyed on both the northern and the southern slopes with different slope percentages (9-10, 13-17, 16-22, 29-31 and 33-37 percent). Soil samples were taken from two depths (0 to 5 and 5 to 15 cm) at four positions with a distance of two meters along the slope during two replications. Finally, 160 soil samples were considered for determination of particle size distribution, organic matter and lime size distribution. The results of this study showed that the surface erosion of the studied area was strongly affected by slope and aspect of the land. In the two-meter position from the top of the slope, there was the highest degree of fine particle erosion but at the bottom of the slope, the relative frequency of fine particles was increased. The surface erosion rate in the southern slopes was on average 23% higher than that of the northern slopes. Also, the results showed that increasing the slope had an incremental effect on the amount of sand and a significant reduction effect on clay content (P < 0.05, R2 = 0.43).