Study on TDR method : Measuring limitation and its applications

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The objectives of this study are to investigate the limitation of the TDR method to various soils, to examine the length of TDR probe, and to develop the application of the method We obtained the following results.1. A review of the TDR method disclosed various problems in terms of soil water measurements.2. Calibration experiments were conducted for three representative field soils in Kyushu Island. The results showed that the estimation by Topp's equation underestimates soil water content for smaller soil bulk density, and that the Maxwell-De Loor model as calibration equation can be successfully applied for different soils.3. A new type of TDR probe was designed using electrical circuit board. Calibration of the probe demonstrated its effectiveness in both dry and wet soil.4. Multiple length TDR probes of metal rods were employed to measure soil water content at different depths. The method was found to be applicable to determine the features of soil water distribution in field.5. Based on the fuzzy theory, we tried water saving control in a drip irrigation experimented in a dry land, and demonstrated the validity of the technique.6. Both soil water content and electrical conductivity were measured using TDR method for glass beads and sand soil. It was found that water content is higher in salt water condition than in distilled water condition, and that the Topp's equation excellently estimates soil electrical conductivity.7. The application of TDR method made it clear that the shading effect is independent of soil water content in mungbean cultivation, and that the water use efficiency is high in intercropping system.