Assessment spatial variability of soil erodibility by using of geostatistic and GIS (Case study MEHR watershed of SABZEVAR)

Soil erodibility is one of the key factors affecting certain sediment and soil erosion models such as USLE, RUSLE and MUSLE, and is represented as K factor that is the function of particle size distribution, organic content, soil structure and permeability. Traditional methods do not depict spatial displacement and fail to provide information on the precision of approximations by these methods. This study was performed to assess spatial variability of soil erodibility and its relevant variables in Mehr watershed, Sabzevar. The sampling network included 110 nested-systematic points with distance about 50, 100, 250 and 500 meter across the study area at GIS. Sampling was done at depth of 0-5 cm beneath the ground surface and permeability was studied at depth of 5-30 cm. Some soil properties such as particle distribution and organic content were measured at laboratory. Spatial variability of these variables were examined with means such as variogram models, kriging and error maps. Statistical analysis of the soil shows that the studied variables following the gaussian, exponential and spherical models and their range were changed from 320 to 3,200 m. Soil erodibility magnitude ranges from 0.13 to 0.91 and maximum and minimum values were identified in the east and southwest of the studied area. Soil spatial variability pattern is highly corresponds the silt pattern due to high effect of silt on soil erodibility. Spatial variability pattern is also in agreement with geological maps satisfactorily that reveals parental materials controls erodibility of soil with respect to the soil's type.