A. Keyhani - Department of Power and Machinery, Faculty of Agriculture, University of Tehran, Karaj, Islamic Republic of Iran.

To measure soil water content (or soil matric suction) in thin layers of about ۳۰mm, conventional gypsum blocks are not suitable. To carry out the task, mini-gypsum blocks were constructed using plaster of Paris in an innovative fashion. A power relationship was found between the soil water content and the mini-gypsum blocks’ readings in kΩ. The calibration results showed that readings of mini-gypsum blocks were sensitive to temperature. A normalized resistance deviation method was adopted to compensate for the effect of temperature on the sensor readings. After calibration, the high coefficient of determination obtained ensured the use of the mini-gypsum blocks for further experiments.

Matric suction, Normalized resistance deviation, Plaster of Paris, Temperature calibration, Water content