Comparing the sediment variation with hillside direction and plot length in storm wise soil erosion

In this study the role of hillside direction and plot length of experimental plots on the accuracy of soil erosion estimation was studied. For this purpose 12 experimental plots with length of 2, 5, 10, 15, 20 and 25 meters were established on the north and south facing hillside of Sanganeh watershed having sandy loam soil texture and mean slope of 30%, located in the northeastern part of Khorasan Razavi province. The sediment of Sanganeh watershed having an area of about 1 ha was collected in concrete ponds and was used for comparison with the test plots. During the research period (November 2006 to June 2007), 12 storms causing runoff occurred and the sediments were collected in metal containers and were analyzed later. The results revealed that the amount of sediment per unit area collected from the south hillside plots was nonlinearly and adversely dependent on the plot length. However, the variation among sediment collected from the north hillside plots was not significant due to difference in crop cover and soil type. In addition, the variation in soil loss was reduced as the plot length increased. According to statistical analyses, the 20 meter plot length was found as the optimal plot length for estimation of soil erosion in the studied watershed.