Runoff Production under the Influence of Slope and Soil Characteristics in Pastures without Vegetation Cover in Semi-Arid Region

Runoff is an important factor influencing soil erosion in slope lands. This study was carried out to investigate runoff production as affected by slope gradient and soil properties in pastures without vegetation cover in Zanjan province during 2017-2018. Nine pastures with slope gradients of 6, 8, 12, 15, 17, 24, 27, 31 and 36% were considered and three plots with 1.0 m× 1.5 m in dimensions were installed in each slope on early autumn 2017. Runoff production was measured in twenty seven plots for a one-year period. The steep slopes have coarse soil textures, low organic matter and low lime content as compared to gentle slopes. Out of thirty two rainfalls, five events caused runoff at the plots. There was no positive trend between runoff production and rainfall intensity, indicating the role of soil conditions such as initial water content in controlling runoff at the plots. Significant difference was found among rainfall events in runoff production. Lower runoff production potential in the lands was associated with lower rainfall intensities and higher soil infiltration rate. Runoff production was significantly affected both slope gradient (r= 0.51, p< 0.01), organic matter (r= -0.69, p< 0.01), and lime content (r= -0.59, p< 0.01). This study indicates the role of soil properties and slope gradient in runoff production in the pastures. Therefore, maintaining vegetation cover can increase water retention and improve organic matter content, resulting in a decrease in runoff production.