Effect of Application of Several Amendments on Threshold and Coefficient of Runoff in Various Conditions under Rainfall Simulation

The major issues that must be addressed in watersheds is correct estimating threshold from the rainfall events. According to the agricultural leveling land and irrigation and drainage network of study area is exposed to sourounding runoff destruction, so watershed management activities such as design of small-scale water structures, sediment control structures, implementing the management actions in vegetation, soil and land utilization is required to understand and estimate surface runoff threshold. The aim of this study was to determine the effect of soil conservation practices on runoff initiation time and runoff coefficient using rainfall simulator in the Arayez plain. For this purpose, a rain simulator with a metal plot that has a square meter area was used. The treatments consisted of natural soil (observed), polyacrylamide at two levels 3 and 6 grams per square meter (P3 and P6, respectively) and Parsian mulch (Pc) that were conducted in sandy clay loam and sandy loam soil with three replications. The rainfall intensities set up to be of 32 and 50 mm per hour in slopes 7.5 and 12.5 percent. For statistical comparison split split plot design was used. Least Significant Difference (LSD) method was used for comparison of means. Results indicated that the mean of runoff initiation time in observed treatment is higher than mulch treatments, it means which runoff begins later in observed treatment. Mulches of P6 and Pc have not significantly differences in runoff initiation time. Runoff initiation time in P3 mulch much earlier began than the other treatments. Also, results revealed that the mean of runoff coefficient in different treatments (observed, P3, P6 and Pc) have a significant differences, and belonged to separate group.