Application of Time Domain Transmissiometry for Measurement of Moisture Content and Void Ratio in a Heavy Paddy Clay Soil.

To establish a versatile farming system for paddy fields with heavy clay soils it is essential to accurately monitor soil moisture Although various moisture monitoring methods have been proposed, an adequate method for heavy clay soils has not been yet established because of their unique dielectric properties. Digital time domain transmission (TDT) sensors were applied for monitoring gravimetric water content (w) and void ratio (e) in a paddy soil. While during the initial rice growth stage the TDT sensors yielded excellent results, some problems were experienced when the soil dehydrated and shrinkage cracks developed in close vicinity of the sensors. The e estimated from w decreased gradually and irreversibly despite repeated rainfall and irrigation. Although more detailed studies regarding optimal sensor placement are required, presented results demonstrate the potential applicability of TDT for monitoring w and e and related geotechnical properties of heavy clay soils.