The possibility of measuring the water content of saline fine textured soils by time domain reflectometry

Measurement of soil water content is done by different methods, which can be referred to methods such as oven method, gamma ray, and time reflectometry methods. Direct methods are time-consuming and lead to handling of the soil sample, and some indirect methods have risks of radiation of radioactive materials. Among these methods, the TDR method, which is one of the reflectometry methods, is a quick and safe method, it has been given attention for this reason and it gives acceptable results in soils with normal conditions. But for saline soils, this method is not able to measure soil water content accurately. The objective of this research is to construct sensors that the TDR device can use to measure the water content of saline and fine textured soils. By making these sensors, it is possible to measure the water content of saline soils with a TDR device, and if an error is observed, the actual amount of soil water content can be obtained by providing suitable calibration models. For this purpose, a fine textured soil was prepared from Tikmehdash research station and by adding different amounts of salt to it, soil samples with electrical conductivity of 20, 35 and 50 dS/m with natural density were prepared. After determining the type of coating suitable for covering the moisture sensor rod, which is a polymer material, through trial and error, the length of the coating used in the middle moisture sensor rod was determined for the mentioned soil with the prescribed salinities in certain water content, which was equal to a length of the moisture sensor rod. Then, the coated sensors were tested to measure other soil water contents, and suitable calibration models were presented. Therefore, by measuring the soil water contents using the TDR method, the water content of fine-textured saline soils can be predicted from the models.