Testing of new inputs to predict near-saturated soil hydraulic conductivity

Near-saturated soil hydraulic conductivity (Ks) is a key property for several purposes including simulation of hydrological processes, determination of unsaturated soil hydraulic conductivity function and modelling water flow and solute transport. Since it is soil structure-dependent, field measurement techniques should be used to minimize disturbance of the sampled soil volume. Because of high spatiotemporal variability of Ks, replicated measurements need to be carried out, so that, the method to be applied should be simple and rapid enough as the simplified falling head (SFH) technique is. Alternatively, pedotransfer functions (PTFs) could also be utilized for indirect prediction of Ks through the surrounding soil attributes. The objective of this study was to test some new inputs to predict the Ks of salt-affected soils adjacent to Lake Urmia. A 32 cm diameter ring was used to determine Ks by the SFH technique in soils with different salinity (electrical conductivity of saturated extract, ECe = 0.1 – 95.3 dS/m) and sodicity (exchangeable sodium percentage, ESP = 4 – 70.9 %) levels. A total of 190 SFH runs were carried out, adjacent to each of which, some undisturbed soil cores (5 cm in height by 5 cm in diameter) and disturbed soil samples were randomly collected from the surface soil and were analyzed for their physicochemical properties. The studied soils mainly had moderate (≈ 40%) to moderately rapid (≈ 48%) conductivities. Correlation and stepwise regression analysis showed that Ks was correlated negatively with bulk density (ρb) (r = -0.205), index of crusting (Ic) (r = -0.180), and degree of compaction (SDC) (r = -0.206) (P ≤ 0.01) and positively with structural stability index (SSI) (r = 0.184) and geometric mean diameter of soil aggregates (GMD) (r = 0.157) (P ≤ 0.05). Furthermore, the Ks had negative correlation with both soil ECe and ESP.