with estimates increasing as much as a factor of 20 when the scale of measurement increased from 0.1 to 2 m (e.g., Estimates of saturated and unsaturated water flow in soil are impor- Garbesi et al., 1996;Tidwell and Wilson, 1999). tant for predictions of infiltration, runoff, and solute transport. Previ-Measurement bias related to sample size has someous research indicates that ponded infiltration estimates are influenced by the volume or cross-sectional area of the measurement. Our study times been attributed to smaller samples having less probcompared quasi-steady infiltration measurements made using 20-, 30-, ability of encountering spatially infrequent, high magniand 45-cm-diameter cylinders driven 25 cm deep into 56 field plots tude portions of the soil (Iverson et al., 2001; Starr et al., under diverse agricultural management practices. Mean infiltration 1995). As pointed out by Sisson and Wierenga (1981), rate increased from 50, to 81, to 95 mm h Ϫ1 as diameter increased. however, this would be a violation of the central limit Standard deviation and range also increased with diameter. All three theorem, since the mean of randomly selected samples diameters produced lognormal data distributions. These results indishould be centered on the same value regardless of their cate that increasing the sample area is not equivalent to pooling of sample volume. If a sufficient number of small-volume many smaller samples, which would have produced the same mean but samples are used, the mean should be equivalent to that with a lower variance. Follow-up experiments with a double-ring configuration or a divider placed in the center of a 45-cm cylinder demon-of larger samples. In terms of the variance, large-volume strated that adding vertical barriers reduced infiltration even when samples should be equivalent to pooling small samples, the total infiltration area was unchanged. A pulse of dye introduced unless the measurement technique creates artifacts de-10 min before removing the ponded water showed an extensive netpendent on the volume or dimensions of the sample. To work of dyed flow pathways in all but the slowest infiltration situaaccount for the decrease in infiltration measured with tions. The pathways were not associated with visible macropores. smaller infiltration rings, Shouse et al. (1994) suggested Careful consideration should be given to the dimensions of samples that a stagnation zone (an artifact of the measurement used to estimate saturated and possibly unsaturated flow from infiltechnique) was introduced when partitions were driven tration experiments.