Effect of soil texture and organic matter on the accuracy of time dimain reflectometry method for estimating soil moisture content

Time Domain Reflectometry (TDR) is One of the modern and accurate methods in determination of soil water content that based on dielectric constant measurement. On the other hand Given that dielectric constant is affected by the soil characteristics، Therefore، calibration and determination of the relationship between dielectric constant and volumetric soil moisture is required for the practical application of this method. The purpose of this research is the evaluation of the effects of soil texture and organic matter on the accuracy of volumetric water content measured by TDR. For this purpose The experiments were carried out on five types of soil texture (sandy، sandy loam، loam، sandy clay loam and clay loam)، and three organic matter levels (2، 3. 5 and 5 percent) which contain litter fertilizer in three repetitions under quite random conditions. In order to evaluate and calibrate the results of the TDR system، soil volumetric water content was also measured by weight method. Results show that the accuracy of the volumetric water content values obtained from TDR system improved by increasing the percentage of clay and soil organic matter، so that TDR system with the relative error percentage (RE) 3. 97 and 11. 79 has been the most and least accurate، for sand with 2 percent and clay loam textures with 5 percent organic matter، respectively.