Slope gradient and land use change are known to influence soil quality and the assessment of soil quality is important in determining sustainable land-use and soil-management practices. In this study, soil quality indices (SQIs) were developed by quantifying several soil properties to discriminate the effects of slope gradient and land use change on soil quality in 480 km2 of agricultural land in Kurdistan Province, Iran. Three soil quality indices (SQIs) were used. Each of the soil quality indices was calculated using two linear and non-linear scoring methods and two soil indicator selection approaches, a Total Data Set (TDS) and a Minimum Data Set (MDS). Nine soil quality indicators: pH, Electrical Conductivity (EC), Organic Carbon (OC), Cation Exchange Capacity (CEC), Total Naturalized Value (TNV), Soil Erodibility (K), Porosity (P), Mean Weight Diameter (MWD), and Bulk Density (BD) and soil loss rate were measured for 110 soil samples (0–30 cm depth). Soil quality indices maps were developed using digital soil mapping methods. The >10% slope class had the highest soil loss rate and highest percentage of soils with very low quality (grade V) based on all SQIs. The results showed that soil quality was better estimated using the Weighted Additive Soil Quality Index (SQIw) (r2=0.78) compared to SQIa (the Additive Soil Quality Index) and SQIn (the Nemoro Soil Quality Index). The agreement values of all SQIs for the non-linear scoring method were higher than the linear scoring method. The mean values of all SQIs and the soil loss rate were higher and lower in rangeland than cropland, respectively, but they were not significantly different because of intensive grazing. Slopes with a large gradient and where land use was converted to agriculture were characterized by low values of SQIs, suggesting a recovery of soil quality through changing to sustainable practices and abandoning over grazing in these areas.
