Abstract: Time domain reflectometry (TDR)is a modern device for quick measurement of soil water content; it has been widely used for monitoring soil moisture status in farmland in recent years. But application of TDR in soils with high contents of salt or clay may result in large errors due to the embedded limitation of the instrument. Calibration is often needed on a site specific basis to improve the measurement accuracy. In order to examine the feasibility of using TDR for soil water content measurement in saline soil environment, the paper presented an experimental study in this paper to compare the differences in soil water contents measured by a TRIME-T3 TDR and the conventional oven-drying method. Soil sampling and onsite observations were conducted on a reclamation area with salinized soils in Shaanxi Province of China. Plastic access tubes of TDR were placed as groups in 2 strip fields; each group has 3 tubes spaced at 20 cm for easy access of the TDR. Of the total 6 monitoring points, manual readings of soil moisture at depth interval of 20 cm were conducted every 10 days; three readings were taken at each point and the averages were adopted as the final values. In the mean time, soil samples were taken for water content measurement with the oven drying method. The results show that soil water contents measured with TDR tended to be higher than those with the oven-drying method, the absolute deviation was in the range of 1-7 cm³·cm^-3, and the relative difference was between 2% and 25%, indicating the need for calibration process. The soil water content measured with the TRIME-T3 and the oven drying method were compared and fitted to a semi-empirical functional relationship, relatively good correlation was found between the two measurement results with R²=0.094 91, indicating that the TRIME-T3 measurements of soil water content were close to the field condition, and a simple linear relationship can be used for calibration. The electrical conductivity (EC)of the soil samples was not significantly correlated with the moisture content of the same soil profile. Further testing of the soil moisture correction function with TDR obtained a correlation coefficient of 0.99, showing promising application of the TDR technology for determining soil moisture in the study area.

Key words: TDR, saline-alkali land, soil moisture content, electric conductivity(EC)