Variability of near-surface saturated hydraulic conductivity for the clay soils of a small Sicilian basin

Proper characterization of saturated hydraulic conductivity, Ks, of clay soils in a hillslope or a basin is still a challenge for soil science. In this investigation, the clay soils of the Maganoce (Sicily, Italy) basin were sampled at 19 sampling sites by the BEST procedure of soil hydraulic characterization. More OM implied less compact conditions (decreasing dry soil bulk density; coefficient of determination, R2 = 0.67), more stability to water of the soil aggregates (increasing water stable aggregates; R2 = 0.83) and, consequently, higher Ks values (R2 = 0.54). Variability of Ks was lower in the steeper zones of the basin than in the flatter ones. A comparison with the Ks data collected in the past with the Simplified Falling Head (SFH) technique at the same sampling points revealed a similarity between the two datasets but also a tendency of this last technique to yield some small Ks values that were not obtained with BEST. Soil disturbance due to ring insertion that SFH requires and/or Ks anisotropy likely contributed to explain this result. In conclusion, organic matter content and topographic attributes can help to plan an effective clay soil sampling strategy. High Ks values are expected to be less uncertain than small values.