Abstract

Tension infiltrometry is a useful in situ technique that is commonly used to determine hydraulic conductivity of the soil near saturation; however, the measurements are time consuming and costly. The aim of this study was to develop a fully automated tension infiltrometer for field use based on already existing designs. Differential pressure transducers were used to automate water level measurements, and the tension settings were automated by a set of solenoid valves. The effects of different design parameters on water level measurement fluctuations created by bubble disturbances (noise) were studied in the laboratory. The differential transducer provided less noisy measurements than the single transducer. The measurement noise was significantly smaller when a large-diameter reservoir was used. The measurement noise was further reduced by using a reservoir system made of two tubes of different diameters slotted into each other. The effect of an increasing flow rate on the water level fluctuations was also investigated. Based on the design parameters tested, three identical tension infiltrometers connected to a single Mariotte bottle were built and tested under laboratory and field conditions. The pressure-dependent hydraulic conductivity, K(h), values for all three replicates applied in the laboratory did not significantly differ from each other. In the field, the infiltration experiments were performed on a sandy loam soil on sites with and without wheel tracks. A significant reduction of K(h) values for most of the applied pressure heads was observed in the wheel track. The improved automated tension infiltrometer requires only a little operator intervention.

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