Assessment of soil quality index for different NDVI ranges in a watershed

The aim of this study is to determine the effect of vegetation density on the soil quality index (SQI) in the Godrahav basin, which varies in terms of land use and topographic features. For this purpose, a total of 180 soil samples were taken at depths of 0–20 cm (surface soil) from six ranges of the normalized difference vegetation index (NDVI) in a typical watershed in Artvin (northeast Türkiye). The SQI was used to evaluate and calculate soil quality in the study area. Topographic features (elevation, slope, and aspect), land use, physical properties of the soil (clay content, silt content, sand content, mean weight diameter, aggregation rate, aggregate stability, porosity, bulk density, dispersion rate, field capacity, and wilting point), and chemical properties of the soil (organic matter content, pH, and EC) were used as indicators. The results showed that aggregate stability, aggregation rate, porosity, field capacity, and wilting point water content were highest in the NDVI range of 0.45–0.56 with values of 89.83%, 76.76%, 60.56%, 47.89%, and 33.98%, respectively. Meanwhile, bulk density was lowest in the same NDVI range at 0.81 g cm–3. The differences among NDVI ranges in terms of soil properties were statistically significant. SQI values varied significantly (p < 0.01) depending on NDVI classes with an increasing trend from the lowest NDVI range to the highest. These results provide a better explanation of the effect of vegetation density on soil quality.