Evaluation of some different types of gypsum blocks for determination of soil moisture

There are several methods for measuring and monitoring the status of soil moisture. One of the cheap methods compared with methods using more expensive devices, is determination of soil moisture status with the aid of a gypsum block. In this method, soil moisture status is determined by measuring the electric resistance of two electrodes embedded in the device. 5 brands of gypsum blocks with different structures were applied. The electrodes comprise of three omocentric cylindrical steal nets. The radiuses of these nets were 25, 15 and 10 millimeters. Gypsum Blocks were classified based on their types (dead, half dead, alive), composition (cement ratios) and the weight of gypsum used in their construction. By careful monitoring of their behaviors in air and soil, the most appropriate kind of gypsum block was selected according to their construction technique, type and ratio of their composites (gypsum and cement), electrode's space, characteristics of initial calibration and validation in the air and its equilibrium status in the soil. The blocks which use cement in structures have uniformity with soil moisture curve. In this study an ELE model 5910A soil moisture meter was used for readin the blocks. And as a result of the comparison of these devices functionality, the ELE soilmoisture meter was recognized as a precise devise for the irrigation management program range. It was also determined that having the initial calibration curve of gypsum block in the air hich is derived from the dimensionless relative moisture versus readings of the ELE, it is possible to measure the soil moisture without calibrating the gypsum block in soil.