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A review on controlled vacuum lysimeter design for soil water sampling

Farsad, A., Sadeghpour, A., Hashemi, M., Battaglia, M., Herbert, S.J.
Environmental technology & innovation 2019 v.14 pp. 100355
algorithms, automation, controllers, energy efficiency, lysimeters, soil profiles, soil water, tensiometers
Measuring water movement in unsaturated soil profile is inherently difficult. Equilibrium Tension Lysimeters have been introduced for collecting representative water samples (in terms of concentration and volume). In this method, suction level in sampler container is adjusted daily with soil matric pressure. Since soil–water tension changes over time, the vacuum level of sampler has to be adjusted accordingly. Automated Vacuum Lysimeters use electronic controllers as well as a set of vacuum sensors to keep the vacuum applied to porous plates in equilibrium with soil matric pressure. Automated Equilibrium Tension Lysimeter has no direct control on matric pressure right above the sampler. Therefore, accuracy of samples is questionable. Controlled Suction Period Lysimeter (CSPL) uses a tensiometer right above water sampler to address this issue. This method seems to be the most reliable method for collecting soil–water samples. However, it has some issues such as low energy efficiency and slow tensiometer response rate. In this review paper, different methods of measuring water movement in unsaturated soil profile are summarized and compared. A low resistance set up and a new controlling algorithm are suggested to significantly increase energy efficiency and accuracy of the system.