Assessing the soil quality index as affected by two land use scenarios in Miandoab region

In this research, the physical, chemical and biological properties of 19 soil indicators using 80 samples (0–25 cm) were quantified to measure the soil quality index (SQI) in Miandoab region, Iran, across different land uses. These properties include aggregate stability (AS), bulk density (BD), soil moisture content (θm), saturation percentage (SP), particle size fractions (clay, silt, sand), pH, EC, available P and K, OC, total N, C/N, CaCO3, sequestration of organic carbon (SOC), CEC, microbial respiration (MR) and microbial population (MP). Principal component analysis (PCA) was used as a dimension reduction method to separate farmlands and orchards as two different land uses. The linear SQI and nonlinear SQI were calculated, and the results showed a clear difference in SQI as affected by the aforementioned land uses. The specific contribution of each minimum data set also showed that soil OC, N, MR, MP, silt, CaCO3, AS and BD had the highest importance to SQI. The linear SQI value was more significantly affected by the physical properties than the chemical and biological ones. It varies from the maximum value of 35.17% in the farmland to 37.74% in the orchard. On the other hand, the nonlinear SQI showed the highest contribution of biological SQI in the farmland (73.94%) followed by the orchard (64.15%). Finally, both linear and nonlinear equations may be acceptable for assessing SQI using the aforementioned soil properties. Furthermore, it is the biological properties that have the main role in terms of evaluating the effect of land use conversion on soil quality.