Temporal and Spatial Changes of Soil Salinity in a part of the 280-Thousand Hectare Drainage Plan Lands of Golestan Province

Soil desalination in drained fields is very important because soil salinity harms on crop yield. Therefore, for the optimal management of water and soil, and the sustainability of agricultural lands, salinity monitoring in soil is essential. In this study, 44 soil samples from the depth of 0-30 and 30-60 cm were prepared from drained lands, during one cropping year. Then, soil salinity and acidity map was produced by GPI, LPL, IDW, Ok, RBF methods. Evaluation of salinity at 0-30 cm showed that stable kriging in the first and third months, exponential kriging in the second month, RBF inverse multi-quadrant model in the fourth and fifth months, were the best models. The results 30-60 cm showed that stable kriging in the first and third month, Gaussian kriging in the second month, Exponential kriging in the fourth month, and RBF inverse multi-quadrant model in the fifth month were selected as the best model. Also, evaluation of pH at the depth of 0-30 cm showed that Spherical kriging in the first month, GPI with the first power in the second and fifth months, IDW with the second power in the third month and Exponential kriging in the fourth month had the lowest RMSE. Evaluation of pH at 30- 60 cm showed that stable kriging method in the first, third, and fourth months and GPI with the first power in the second and fifth months had the lowest RMSE. The problem of salinity and alkalinity was observed in most of the surveyed region, and the level of salinity in the surface layer of the soil was higher than in the deep layer. The comparison of the salinity map in different months shows that the salinity has been decreasing during the 5 months of monitoring and the general trend of pH changes is similar to EC.