Characterizing Spatial Variability of Soil Properties in Tigris Basin Using Geostatistics and Geographical Information Systems

Abstract

Assessment, evaluation and mapping of the spatial characteristics of soil properties are crucial to ensure the sustainability of plant production and the development of appropriate management practices in the areas of intensive agricultural production. In this study, some physical and chemical soil characteristics of Dicle Basin, where most of the water reserves of our country are located, and large irrigation projects are taking place, were determined and spatial distributions are modeled and mapped. One hundred seventy-five soil samples from Diyarbakır and Siirt provinces were collected from 0-20 cm depth at approximate corners of each 5 x 5 km grids. Coverage of study area was 4.341 km2. In order to make a more accurate estimation of the changes of soil properties at distances shorter than 5 km, 33 soil samples were taken at 250 m, 750 m and 1750 m distances between two consecutive grid points. Soil samples were analyzed for texture (sand, clay and silt contents), organic matter (OM), lime content, soil reaction (pH), electrical conductivity (EC), available phosphorus and extractable potassium (K). The modeling of spatial variability allowed to predict the soil characteristics of locations that were not sampled and spatial distribution maps was created. The lowest variability in the study area was found for pH (CV=3.9%) and the highest variability was on available phosphorus (CV=137.8%) concentration. The highest range value was obtained for EC (135.4 km) while the smallest range value was obtained for pH (4.74 km). The soil maps where the lowest and highest values of each soil characteristic can be easily detected are extremely useful to determine appropriate management methods, remediate problems and optimize the use of inputs.

Keywords

• Tigris Basin soils
• geostatistics
• spatial variability
• semivariogram
• soil management