AbstractLaboratory experiments were conducted to examine the radius of soil (sand) sampled (Sr) by a porous cup sampler. Srwas defined by the detection of potassium bromide (KBr) in a sample when KBr was injected at horizontal distances of 5, 10, 15, 30, and 45 cm from the sampler. For quasi‐static soil moisture conditions, the relation between Sras defined by the arrival time of KBr (t) at the sampler (evacuated with a constant vacuum of 70kPa) after it was injected at a distance (x) was described by t = 1.4x2.3.As expected, desaturation occurred most rapidly near the sampler (0‐5 cm). The amount of KBr collected on a mass balance basis was greatest when KBr was injected near the sampler and decreased with injection distance. The injection of KBr into the soil at a prescribed distance from the sampler was a better method for predicting Srfor a given time than change in matric potential of the s
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