Trends of Soil Salinity Changes and Its Relation to Climate Variables (Case Study: Karaj)

This research was used from climate information such as average humidity, average wind speed, soil temperature and salinity of different soil depths (5, 10, 20, 30, 50, and 100 centimeters) in 10 years (2008-2017). The purpose of this study was to investigate the relationship between climate parameters and soil salinity fluctuations. For this purpose, rice soil salinity data were used which were previously measured. In both seasons of rice cultivation (conducted in one of the nurseries of Alborz province), salinity fluctuations at different depths of soil were recorded over a period of five to seven days, and soil salinity required for the purposes of this study was obtained, and then with the required meteorological data, the research was done. Also, Hurst test to find enough variance of the data to analyze the time series trend, and Mann-Kendal, spearman, and multivariate regression tests were applied for data analysis. The results showed that all parameters of the study based on the Hurst coefficient bigger than 0.5, had a significant variance for time series analysis. The results of Mann-Kendal and spearman tests showed that in surface soil layers (5 and 10 cm) after 10 years period, the soil salinity had a descending trend. However, both tests had an increasing trend in deeper layers (20, 30, 50 and 100 cm) and at depths of 50 and 100 cm observed the significantly increasing trend at a 5% level. Result of the multivariate regression test illustrated that the temperature in depth of 5 cm and average relative humidity (each 16%) and average speed of 60% had the most and the least effect, respectively on the soil salinity in the mentioned soil depth. Also, in four depths of six depths, the temperature in depth of 5 cm was the most effect on soil salinity of different soil depths. As a general result, in areas where the conditions of this present study, cultivation of plants with surface roots is possible because salinity fluctuations in the surface layers are low and it does not pose a threat to the plant under cultivation but crop cultivation with deep roots is limited because salinity fluctuations is an increasing trend that should be addressed so that soil salinity does not have a detrimental effect on plant yield.