Study of spatial variability and mapping of soil salinity in agricultural lands using kriging and GIS in south of Tehran

Using low quality water on agricultural lands in South of Tehran has increased the risk of soil salinity and created problems for some agricultural crops. This study was carried out to determine of soil salinity distribution and to produce salinity map. The mapping of salinity can also identify the saline and non-saline regions that are very effective for land management and choosing kind of crops that are suitable. The study area is located in 20000 ha of lands in South of Tehran between expressways of Azadegan، Tehran- Qom and Tehran- Saveh. In order the soil salinity mapping، 196 surface soil samples (0-30cm) were taken from a regular grid of 1000×1000m. The electrical conductivity of saturated soil extract (ECe) was measured. Data analysis and soil salinity mapping has been done by GIS and kriging interpolation method. The results showed that ECe varies between 0. 2-14dS/m. Based on the soil salinity map، ECe of 0-2، 2-4، 4-8 and 8-16dS/m have covered 30. 41، 42. 44، 22. 63، and 4. 52 percent of the total area، respectively. The best model was fitted the exponential which has been achieved with a range of 1130 meter. Considering the threshold of salinity for many vegetable crops is less than 4 dS/m، thus increasing salinity to more than 4dS/m is worrying. The results showed that the soils of study area، due to differences in the depth of groundwater، relief، using low quality water in shallow wells، river، sewage water for irrigation، were affected on soil salinity.