University of Tehran Press Iranian Journal of Soil and Water Research 2008-479X 56 2 2025 04 21 The challenges of measuring and estimating the soil erodibility factor (K) of the (R)USLE model in rangelands of arid regions The challenges of measuring and estimating the soil erodibility factor (K) of the (R)USLE model in rangelands of arid regions 351 371 101766 10.22059/ijswr.2024.386195.669845 FA Ayoub Avizhgan Soil Science Dep., Faculty of Agriculture, University of Tehran, Karaj, Iran Hossein Asadi Soil Science Dep., Faculty of Agriculture, University of Tehran, Karaj, Iran Mahmood Arabkhedri Soil Conservation and Watershed Management Research Institute (SCWMRI), Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran Hamzeh Noor Khorasan Razavi Agricultural and Natural Resources Research Center, Agricultural Research, Education and Extension Organization (AREEO), Mashhad, Iran Ali Akbar Nazari Samani Department of Arid and Mountainous Regions Reclamation, Faculty of Natural Resources, University of Tehran, Karaj, Iran Journal Article 2024 11 29 This research aimed to determine the soil erodibility factor (K) of the Universal Soil Loss Equation (USLE) by direct measurement of soil loss at natural runoff plots (), and to compare it with the estimated K by the USLE-nomograph (). The research carried out at the Sanganeh Soil Conservation Research Site located in the northeast of Iran, in dry rangelands. The soil loss data were obtained from 19 plots with lengths of 20 and 25 m, and different conditions in terms of soil, slope, vegetation cover, and rock fragments under 20 natural rainfall events. The results showed that average intensity and the maximum 30-minute intensity had a greater correlation with soil loss compared to the . Based on the results obtained,  is at least 24, 7, and 6 times of , obtained using the soil loss data of the long-term average, the year with the largest share, and the most intense event (), respectively. The main reasons likely for this overestimation are the low intensity of erosive events and the resulting uncertainties in the measurement of soil loss and other USLE model factors in dry rangelands. Therefore, based on the overestimation of the USLE nomograph, more research, especially with a longer statistical period or using a rainfall simulator with an intensity of 63 mm h^-1in field, is needed to develop appropriate relationships to estimate the K factor in rangelands in dry regions. This research aimed to determine the soil erodibility factor (K) of the Universal Soil Loss Equation (USLE) by direct measurement of soil loss at natural runoff plots (), and to compare it with the estimated K by the USLE-nomograph (). The research carried out at the Sanganeh Soil Conservation Research Site located in the northeast of Iran, in dry rangelands. The soil loss data were obtained from 19 plots with lengths of 20 and 25 m, and different conditions in terms of soil, slope, vegetation cover, and rock fragments under 20 natural rainfall events. The results showed that average intensity and the maximum 30-minute intensity had a greater correlation with soil loss compared to the . Based on the results obtained,  is at least 24, 7, and 6 times of , obtained using the soil loss data of the long-term average, the year with the largest share, and the most intense event (), respectively. The main reasons likely for this overestimation are the low intensity of erosive events and the resulting uncertainties in the measurement of soil loss and other USLE model factors in dry rangelands. Therefore, based on the overestimation of the USLE nomograph, more research, especially with a longer statistical period or using a rainfall simulator with an intensity of 63 mm h^-1in field, is needed to develop appropriate relationships to estimate the K factor in rangelands in dry regions. https://ijswr.ut.ac.ir/article_101766_1ba2ba28d241b42b944da82c1ed16cae.pdf