Efficiency test of modeled empirical equations in predicting soil loss from ephemeral gully erosion around Mubi, Northeast Nigeria

A field study was carried out to assess soil loss from ephemeral gully (EG) erosion at 6 different locations (Digil, Vimtim, Muvur, Gella, Lamorde and Madanya) around the Mubi area between April, 2008 and October, 2009. Each location consisted of 3 watershed sites from where data was collected. EG shape, land use, and conservation practices were noted, while EG length, width, and depth were measured. Physico-chemical properties of the soils were studied in the field and laboratory. Soil loss was both measured and predicted using modeled empirical equations. Results showed that the soils are heterogeneous and lying on flat to hilly topographies with few grasses, shrubs and tree vegetations. The soils comprised of sand fractions that predominated the texture, with considerable silt and clay contents. The empirical soil loss was generally related with the measured soil loss and the predictions were widely reliable at all sites, regardless of season. The measured and empirical aggregate soil loss were more related in terms of volume of soil loss (VSL) (r2=0.93) and mass of soil loss (MSL) (r2=0.92), than area of soil loss (ASL) (r2=0.27). The empirical estimates of VSL and MSL were consistently higher at Muvur (less vegetation) and lower at Madanya and Gella (denser vegetations) in both years. The maximum efficiency (Mse) of the empirical equation in predicting ASL was between 1.41 (Digil) and 89.07 (Lamorde), while the Mse was higher at Madanya (2.56) and lowest at Vimtim (15.66) in terms of VSL prediction efficiencies. The Mse also ranged from 1.84 (Madanya) to 15.74 (Vimtim) in respect of MSL predictions. These results led to the recommendation that soil conservationists, farmers, private and/or government agencies should implement the empirical model in erosion studies around Mubi area.