Comparison of Time Domain Reflectometry, Capacitance Methods and Neutron Scattering in Soil Moisture Measurements

An accurate¡ precise¡ fast and ease as well as the ability for measurements in depth are the characteristics that are desirable in measuring soil moisture methods. To compare methods (time domain reflectometry and capacitance) with neutron scattering for soil water monitoring¡ an experiment was carried out in a randomized complete block (RCB) design (Split Split plot) on tomato with three replications on the experimental field of IAEA (Seibersdorf-Austria). The treatment instruments for the soil moisture monitoring (main factor) consist of neutron gauge¡ Diviner2000¡ time domain reflectometer (TDR) and an EnviroScan and different irrigation systems (first sub factor) consist of trickle and furrow irrigations and different depths of soil (second sub factor) consist of 0-20¡ 20-40 and 40-60cm. The results showed that for the neutron gauge and TDR the amount of soil moisture in both of trickle and furrow irrigations were the same¡ but the significant differences were recorded in Diviner2000 and EnviroScan measurements. The results of this study showed that the neutron gauge is an acceptable and reliable means with the modern technology¡ with the precision of ±2mm in 450mm soil water to a depth of 1.5 meter and can be considorelas the most practical method for measuring soil moisture profiles and irrigation planning program. The TDR method in most mineral soils¡ without the need for calibration¡ with an accuracy ±0.01m3m-3 has a good performance in soil moisture and electrical conductivity measurements. The Diviner2000 and EnviroScan are not well suitable for the above conditions for several reasons such as much higher soil moisture and a large error measurement and also its sensitivity to soil gap and to small change in the soil moisture in comparison with the neutron gauge and the TDR methods.