Application of γ-ray computed tomography to evaluate the radius of influence of soil solution extractors and tensiometers

Tensiometers and soil solution extractors are tools commonly used in irrigated agriculture and in studies of soil solute movement. The matric potential (Ψm) measured through tensiometers represents the energy by which water is retained by soil matrix. A relevant aspect that has to be taken into account while evaluating any instrument based on the use of sensors, like the porous cup of tensiometers, is the interference of the sensor on the property that is being measured. Information related to the range of influence of the sensor, its response power and its operation become very important when one is looking for precise results. The objective of this study was to evaluate the region of influence of tensiometer and solution extractor porous cups used in soil physical measurements. A first-generation γ-ray scanner was used having a 241Am γ-ray source and a 7.62 × 7.62 cm NaI(Tl) scintillation crystal detector coupled to a photomultiplier tube. Image analysis and tomographic unit distributions could successfully be used for visualizing soil water content changes around the porous cup and for verifying its range of influence. The results show that computed tomography technique is a valuable tool because it makes it possible to provide an insight about the soil water content spatial distributions around the porous cup of tensiometers and solution extractors. The way that soil water content and matric potential are affected by these sensors was shown by this study.