Document Type : Research Paper
Assistant Professor, Soil Science Department, Faculty of Agiculture, University of Zanjan, Zanjan, Iran
Former M.Sc. Student, Soil Science Department, Faculty of Agiculture, University of Zanjan, Zanjan, Iran
Runoff production along with rainfall characteristics and soil properties is affected by the soil type. This study was carried out to investigate runoff variations as affected by the same rainfall events in different soil textures in Zanjan province. After initial tests, ten soil textures were recognized in the area and accordingly soil samples were taken from 0-30 depth. The experiment was done in the randomized complete block design with ten treatments at three replications. The soils were filled within the plots with a dimension of 60 × 80cm and 20 cm-depth on a sloped land (8%). Experimental plots were exposed to 10 simulated rainfalls with 55-mm h-1 intensity and 30-min duration. Soil moisture content was measured at the plots before each event using the weighted method. The initiation time and volume of the generated runoff were measured at the plots in each rainfall event. The results showed that there was significant differences among the soils in the initial soil moisture (P<0.001), runoff initiation time (P<0.001) and runoff depth (P<0.001). Rainfall events also significantly affected the moisture content (R2=0.98, P<0.001), initiation time (R2=0.95, P<0.001) and runoff depth (R2=0.96, P<0.001) in the soils. From the first rainfall event to the forth event, the soil moisture content and runoff depth significantly increased and the runoff initiation time considerably declined. After the fifth event, the runoff parameters did not significantly vary probably due to the stop of the aggregates breakdown. Based on the results, both the runoff production and the runoff initiation time were remarkably related to the soil moisture content (R2=0.96, P2=0.94, P<0.001, respectively).