Measuring Soil Water Content and Electrical Conductivity Under High Salinity Conditions Using a Novel TDR Method

Measuring Soil Water Content and Electrical Conductivity Under High Salinity Conditions Using a Novel TDR Method

National Institute for Water Resources, Water Resources Research Institute Program

3/1/2010 – 2/28/2011

Salt accumulation from irrigation is a significant and growing problem on many agricultural lands. The efficient operation of an irrigation system relies on, among other factors, the correct reading of soil water content, which is currently an imperfect process especially in high-salinity soils. WRRC Research Associate Dr. Xiufu Shuai worked on the development of a new approach to measure water content based on the time domain reflectometry processes.

Problem and Research Objectives:

Approximately one-third of the developed agricultural land in arid and semi-arid regions reflect some degree of salt accumulation, while more than 25% of the 47 million acres of irrigated agricultural land within the U.S. is affected by salinity (Allison 1964, Tanji 1990). Determining the accurate measurement of soil water content and electric conductivity (EC) in highly saline soils can improve the practical operation of irrigation systems, guide the installation of drainage systems, and provide fundamental information for establishing and validating the algorithm of microwave remote sensing of soil moisture. However, the widely used nondestructive in-situ method, time domain reflectometry (TDR), failed to work under high salinity condition. Feng et al. (1999) proposed an alternative inverse analysis method to analyze the data from the TDR measurements in the frequency domain. They developed a model, the scatter function of a multi-section transmission line, which can theoretically be applied to any salinity condition. This theoretical model estimates the dielectric permittivity (DP), which is then converted to soil water content by calibration. However, there was no published material that specifically explores using the inverse analysis method under high salinity conditions.

The following were the objectives of this research study:

1. Applying the inverse analysis method proposed by Feng et al. (1999) to measure soil water content and EC under highly saline conditions.

2. Examining the accuracy and upper limit of measurability by the inverse analysis method using commercial probes.

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