Evaluation of soil quality with different methods in upper tigris basin where intensive agricultural production is performed

Sustainability in regions where intensive agricultural production is carried out can be achieved by determining the soil quality accurately and developing management methods accordingly. The purpose of this study was to determine the soil quality index of the Upper Tigris Basin by using different methods and mapping of the spatial variability with geostatistical methods. The study area of 9847,29 km2 with 5 different land uses was divided into 5km * 5km grids and soil samples were taken from 386 points at a depth of 0-20 cm from approximately the corners of grid points. Additional soil samples of 66 points were taken between the grid corners (250m, 750m and 1750m) in order to define the variations in distances less than 5 km. Particle size distribution (clay, sand and silt), aggregate stability (AS), pH, electrical conductivity (EC), organic matter (OM), available phosphorus (P) and potassium (K), sodium adsorption ratio (SAR), lime content, bulk density (Bd), available water content (AWC), total porosity (TP) and water filled pore space of soil samples and the mean slope of each sampling area were determined. The parameters were evaluated by Principal Component Analysis (PCA) method, and the minimum data sets (MDS) including the indicators that best represent the soil quality were created. The weights used to express the contribution of the parameters included in the minimum data set to the soil quality were determined by both the PCA and Analytic Hierarchy Process (AHP). Thus, three soil quality index (SQI, SQIPCA and SQIAHP) values were obtained by three different methods. Results of the statistical analysis indicated that soil quality indexes were significantly different from each other. The most significant parameter contributed to SQIAHP (expert opinion) was texture (22%), while the lime content (4%) was the least contributed parameter. The evaluation made for the different land uses showed that field crop fields and the orchards had the worst SQI values. The OM content, AS, Bd, pH and EC had significant effects on soil quality index in the areas where intensive agricultural production was carried out. The findings revealed that soil quality can be determined more accurately by including the expert opinions into the assessment process.