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Water erosion has been recognized as a major soil degradation process worldwide. This is of special relevance in the semi-arid areas of South Bulgaria with long periods of drought along with severe rainfall events. The main objective of this study was to evaluate the applicability of Bromus innermis L. and Lotus corniculatus L. for soil protection purposes under different site conditions. The site parameters considered were slope, fertilization and a range of soil physical parameters. The plant parameters were canopy cover, biomass, and root morphological characteristics. The experiment includes plots without and with eleven rates of NPK fertilization on gentle (6 degrees) and steep slopes (12 degrees). It was observed that the effect of fertilization on shoot and root growth was stronger on the gentle than on the steep slopes. The biomass accumulation was more sensitive to N than the PK fertilizer applications. The increase of the root density with increasing fertilization rates was more pronounced for the mass than for length or surface area. A significant effect on root diameter was found only for the variants with the highest N application. Treatments with the highest root mass density on both slopes showed the greatest potential for reducing erosion.