Accurate measurement of soil moisture helps in better planning for the amount and duration of water applied to the farms, improving irrigation efficiency and preventing degradation of soil and water quality. The time domain reflectometery (TDR) is a relatively new and easy method of estimating volumetric moisture content in soil based on electromagnetic waves movement through the soil. By inclusion of soil compositions in the TDR calibration curves the accuracy of soil moisture estimation increases. Because of the significant impact organic matter on bulk density and surface area of soil particles, calibration curves in organic and non-organic soils are different. In this study, disturbed samples of three soil types with light, medium and heavy textures and with high organic matter were tested in pots of 25.5 cm height and 25 cm diameter. Tested soils range included clay-sand to loam-clay-sand with bulk densities between 0.87 and 1. Comparison of the volumetric moisture content, obtained from TDR calibration curve and weight method, shows high correlation between them. Besides, analysis of the observed data analysis by curve fitting showed that a cubic form described the relationship between the TDR dielectric constant and soil moisture content.
