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Hello, We have integrated some hardware parts for a soil moisture measurement Time Domain Reflectometer. Firsts preliminary measurement confirm us that TOPP equations do not fit exactly our local soils. We think K=f(moisture) is an averaged 3rd order polynomial function fit. But experimental inverse polynomial that fits moisture=g(K) have large differences respect K=f(moisture). In 1980 perhaps was the best solution between accuracy and computing time. Does anyone know more recent references that solve this problem? Some commercial products solve these discrepancies with tables between K (measured TDR relative permittivity) and specific soil moisture content. Is it the best solution? This implies a previous soil calibration. ............ Connecting to last days messages these problems also apply to FDR techniques as ThetaProbe soil moisture sensor however use 5th order polynomial sometimes and different coefficients. Thanks for all, Josep Maria 17-XII-96 -- Josep Maria Torrents-Dolz, Departament d'Enginyeria Electrònica, Universitat Politècnica de Catalunya, c/. Gran Capità s/n edifici C4, 08034 Barcelona, Spain, tel. 34-3-401 67 58, fax 34-3-401 67 56, e-mail torrents@eel.upc.es