Is the Tension Beneath a Tension Infiltrometer What We Think It Is?

The tension infiltrometer has become a standard tool for measuring near-saturated soil hydraulic properties. The objective of this study was to examine the dynamics of the supply tension at the interface between the tension infiltrometer and the measured soil using a pressure transducer under different soil conditions and to raise some cautions needed for proper use of this standard device. Infiltration experiments were conducted on a tension table, a large sand column, and in two field soils of contrasting textures and structures to test the performance of the standard two-piece infiltrometer. Results showed that during high flow rates (>200 cm³ min⁻¹) the tension at the infiltrometer–soil interface started to deviate by as much as 15 mm from the desired tension. However, during field experiments the high flow rates were not experienced, and thus no deviation was observed between the preset desired tension and the actual measured tension at the infiltrometer–soil interface. To alleviate the problem of tension deviation under high flow, the water supply tubing and fitting diameters of the standard infiltrometer were successfully increased to yield a higher flow rate (≈300–400 cm³ min⁻¹) without elevated tensions.