Measurement of soil water content for different soil types by using time domain transmission technology

According to the disadvantages of time domain reflectometry (TDR) on measuring water content for saline soils, high organic matter soils and red soils, a laboratory experiment was conducted to study the applicability of time domain transmission (TDT) instrument for measuring soil water content for different soil types. The results showed that there was a good linear relationship between soil volumetric water content and TDT voltage output for aeolian soils, cinnamon soils and fluvo-aquic soils. An uniform calibration relationship could be established for above soil types with a standard error of estimate of 0.026 cm3·cm-3; The linear relationship between soil volumetric water content and TDT voltage output was still hold for saline soils (EC value of 11.12 dS·m-1, salinity content of 59.5 g·kg-1) with a standard error of estimate of 0.025 cm3·cm-3; For chestnut soils (organic matter content of 67.95 g·kg-1) and red soils, the relationships between soil volumetric water contents and TDT voltage outputs were the cubic polynomials, with the standard errors of estimate of 0.028 cm3·cm-3 and 0.015 cm3·cm-3, respectively. Therefore, TDT instrument can be used to measure soil water content for many types of soils, and presents more superior performance for saline soils, high organic matter soils and red soils comparing with TDR.