A soil quality index for evaluation of degradation under land use and soil erosion categories in a small mountainous catchment, Iran

Soil erosion and land use type have long been viewed as being particularly important drivers of soil degradation. The objectives of this study, therefore, were to select a new soil quality index (SQI) which varies significantly with land use/soil erosion, and to evaluate the new SQI using expert opinion. In total, 18 soil physical, chemical, and biochemical properties (indicators) were measured on 56 soil samples collected from four land use/soil erosion categories (rangeland/surface erosion, rangeland/subsurface erosion, cultivated land/surface erosion and dry-farming land/surface erosion). Principal component and classification analysis (PCCA) identified five PCs that explained 77.7% of the variation in soil properties with the biochemical PC varying significantly with land use/soil erosion. General discriminant analysis (GDA) selected urease and clay as the most sensitive properties distinguishing the land use/soil erosion categories. The GDA canonical scores for the new SQI were significantly correlated with expert opinion soil surface summed scores (for soil movement, surface litter, pedestalling, rills and flow pattern) derived using the U.S. Department of the Interior Bureau of Land Management (BLM) method. A forward stepwise general regression model revealed that the new SQI values were explained by soil movement, surface litter, and the summed values of the soil surface factors. Overall, this study confirmed that soil quality in the study area in Iran is controlled by land use and corresponding soil erosion.