Mapping Water Salinity and Sodicity Using Selected Geostatistical Methods, Case Study: Kerman Plain

Proper design and management of irrigation systems requires knowledge of soil infiltration rate، which is in turn influenced by water salinity and sodicity. The objectives of this study were to investigate the spatial variability of irrigation water electrical conductivity (EC) and sodium adsorption ratio (SAR) and to map these parameters using geostatistical methods. The main objective was to predict the spatial distribution pattern of soil infiltration rate over the study area based on water salinity and sodicity. Water samples were collected from 76 observations wells in the Kerman Plain in 2008. The geostatistical methods used were ordinary and log-normal kriging. The performance of interpolation methods was evaluated through cross-validation with comparison criteria of root mean square error (RMSE) and mean absolute error (MAE). Geostatistical analysis showed that both EC and SAR had strong spatial correlations، and these fitted a spherical model. The cross-validation results are indicated that the two methods provided similar accuracy for estimating salinity and sodicity. Furthermore، it was evident from the kriged maps generated through both methods for EC and SAR that the estimation error maps produced were only slightly different. Therefore، whenever the aim is to produce only a map of spatial distribution of soil properties، ordinary kriging، which is mathematically simpler than other methods، is preferred. Soil infiltration rate distribution pattern was also predicted based on the kriged maps of EC and SAR، and، some approved standards. The results indicated that most of that area، including northern and western regions had good infiltration rates. The rest، which cover mostly the northeastern and southeastern of the study area، had moderate infiltration rates.