Comparing Interpolation Methods for Estimating Spatial Distribution of Topsoil pH and EC (Case Study: Karimabad Rangelands, Hamadan Province, Iran)

Soil alkalinity and salinity are serious problems in arid and semi-arid regions, and therefore monitoring of soil pH and electrical conductivity (EC) is necessary in any region. The present study aimed to properly interpolate soil pH and EC as soil quality indices in a semi-arid mountainous area with annual precipitation of 342.4 mm. The study area is the Karimabad rangelands in Hamadan Province, western Iran. A total of 266 composite soil samples were collected from 0-25 cm soil depth in a systematic random design. Soil samples were processed for pH and EC analysis and then further used for interpolating based on the optimal interpolation method for the study area. The overall soil pH and EC ranged from 7.3-7.9 and 0.33-2.13 dS m-1, respectively, presenting the slightly alkalinity and salinity problem in the region. The results showed the accuracy of spatial prediction of interpolation methods, particularly inverse distance weighting and radius basis function. However, based on root mean square error, the radius basis function was the most appropriate interpolation method to predict spatial distribution of soil pH and EC of topsoil in the study area. While salinity and alkalinity were low, still monitoring these soil indices is highly recommended to prevent the salinization and alkalization in the study area.