Investigation of Time Domain Reflectometry (TDR): Its applicability to irrigation scheduling, and evapotranspiration estimation in Canterbury, New Zealand

Abstract

Time Domain Reflectometry is a relatively new technique for measuring soil moisture content and has not yet been proven as a reliable tool for routine field measurements. This thesis presents results to show that the TOR calibration is valid, from comparison with both gravimetrically sampled moisture contents and neutron probe moisture contents. The TDR does have limitations, such as the maximum waveguide length and the inability to insert waveguides in stony soils, and these are discussed. The project investigates TDR, as applied to irrigation scheduling, for measuring the actual evapotranspiration (ETA) of a crop and is compared to various methods of calculating the potential evapotranspiration (ETP). The methods of calculating ETP, from meteorological data and from weighing Iysimetry, are also investigated. The Lincoln University weighing Iysimeter is the only one on the Canterbury Plains and is the bench mark method for calculating ETP and is shown to be higher than both the Penman and Priestley-Taylor methods.