Comparing field-saturated soil hydraulic conductivity determined by the single-ring pressure infiltrometer and bottomless bucket methods

Reliable estimates of field-saturated soil hydraulic conductivity, Kfs, are challenging because results may depend on the measurement method. In this investigation, Kfs values obtained with the single-ring pressure infiltrometer (PI) and bottomless bucket (BB) methods were compared across three agricultural sites (two sandy-loam soils and one clay soil). At each site, 15 PI runs were performed using two consecutive ponding depths of water (5 and 10 cm) and 15 BB falling-head runs were carried out with repeated declines in ponding depth from 10 to 1 cm. The PI data were analyzed using both the two-ponding-depth (TPD) and one-ponding-depth (OPD) approaches. The Kfs values were predominantly log-normally distributed, whereas the sorptive number α* was normally distributed. The estimated α* values were consistent with expectations based on soil texture (≈4.7 m−1 in the clay soil and 9.7–16.4 m−1 in the sandy-loam soils). The mean Kfs values differed by up to a factor of 1.2 in the two sandy-loam soils (70–85 and 249–293 mm h−1, respectively) and by 1.9 times in the clay soil (150–279 mm h−1). Coefficients of variation ranged from 27% to 130%, with the largest variability observed in the clay soil. Overall, the agreement between the PI and BB methods was satisfactory in sandy-loam soils but less in the clay soil. Method-dependent differences were more pronounced for Kfs variability than for mean values. These results support the BB method as a practical option for high-replication Kfs surveys, while highlighting the need for careful application and data interpretation in fine-textured soils.