عنوان مقاله [English]
Evapotranspiration as an important component of the hydrologic cycle plays a large role in watershed’s water balance study. Accurate estimation of evapotranspiration rate is essential for efficient management of irrigation, determination of plants water demand as well as design of irrigation systems. The aim of the current study is to design and construct a weighing lysimeter to address the need for accurate monitoring of evapotranspiration. The designed lysimeter in this research contains two concentric cylinders. The internal cylinder is the main container of the lysimeter and outer cylinder has the role of protection and isolation of the main container from surrounding soil media. The main container is open-ended from top, but sealed in sidewalls and bottom end, except for orifices at the bottom end to drain the saturation excess water from main container. The main container was made from 3 mm and 6 mm thick steel sheets for sidewall and bottom, respectively. The inner diameter and depth of the main container were 45 cm and 60 cm, respectively. After filling with soil, the containers were loaded on relatively precise and cheap loadcells fixed to a rigid metal framework. An electronic board, which can support four loadcells, was developed for calibration of loadcells and setting up the monitoring and recording the output signals of loadcells as a text file saved on an external memory card. The board can display the instantaneous weight of containers and save them at user defined intervals. The results of performance evaluation indicated that the developed lysimeter can measure and record temporal changes of soil moisture with an acceptable accuracy.