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Development and evaluation of new sensor devices for soil water matric potential measurement


Soil water sensors have great importance for irrigation management and other applications. For this, there are two parameters used, the soil water content and the soil water matric potential (È). For water content determinations there are many sensors available, covering the full range of measurements, different soil types and conditions. Nevertheless, È sensors are more limited in terms of operational range, cost, maintenance and commercial availability. Two new sensor concepts for measuring È were recently developed, named dihedral sensor and IGstat sensor, which presents great potential for low-cost sensors developments for irrigation control and other applications. The dihedral sensor is formed of 2 glass plates in a dihedral angle and a thin water film between them. In contact with a soil, the measured water film length provides È, according to Yang-Laplace equation. The IGstat sensor is formed of an outer ceramic cup with high bubbling pressure and an inner core of glass beads microspheres. Air pressure or light reflection measurements in the sensor core allow assessment of È. At the current stage of development the sensor readings are taken manually, it has been used for thresholding irrigation only, were not thoroughly field tested (both) and little is known about temperature and soil salinity effects on the sensor response. Thus, this project proposes to develop new devices for the continuous measurement of È in soils using these 2 new sensor concepts and evaluate their performances in field conditions. The main expected results are: i) Development of optical and electrical devices for automatic measurements of dihedral sensors; ii) Performance evaluation of IGstat sensors for thresholding irrigation; iii) Development of methods and new devices for continuous measurement of È using IGstat sensors in pneumatic and optical modes; iv) Determination of operational ranges and accuracies for the dihedral and IGstat sensors in field, including evaluations of temperature and soil salinity effect on the sensor responses. (AU)

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