Assessing Soil Degradation: A Comprehensive Study Using Soil Degradation Index (SDI) in a Watershed

Soil degradation is an important problem for watersheds that contain agricultural and natural areas within its border. This study was conducted to assess land degradation status with an empirical method named soil degradation index (SDI) in a watershed. For this purpose, the watershed was divided into transects at 500m intervals in the north-south and east-west directions. After removing the hard-to-reach points due to topography, disturbed and undisturbed soil samples were taken from 138 sample points at the intersection of the transects. In the calculation of SDI, grain size distribution, aggregate stability, aggregation rate, mean weight diameter, dispersion rate, bulk density, porosity, field capacity, wilting point, organic matter content, pH, and electrical conductivity were used as parameters. This study also determined the spatial distribution of these parameters. Some features of the watershed, such as slope, elevation, aspect, and land use, were mapped using the GIS technique. The geostatistical technique was used to interpolate these futures and SDI. The results of the study showed that soil degradation could be expressed with an index value, and basic soil properties can be used as index parameters. These parameters affect index values with different weighting, and these weighting values can be calculated by correlation analysis. Moreover, according to the distribution maps, SDI showed spatial variability due to the land use, altitude, and aspect, but it did not vary regularly due to the slope.