Measuring and Estimating Soil Hydraulic Properties in a Farmer's Field, Western Kentucky.

Soil hydraulic properties are relevant for quantitative analysis and modeling of water and solute transport through the vadose zone. Measuring hydraulic properties can be expensive and time consuming. Pedotransfer functions (PTFs) have been developed and are increasingly used to estimate hydraulic properties by more easily measured data (such as soil texture, bulk density). However, the validation of a PTF outside of its development dataset can be problematic. Therefore, the objective of this study was to evaluate PTFs in a farmer’s field in Western Kentucky. Undisturbed soil cores were collected from 10 soil profiles at five depths in a field soil in Princeton, Kentucky for measuring soil hydraulic properties. Saturated hydraulic conductivity (K_sat) was measured with a permeameter. Near saturated hydraulic conductivity was measured in double pressure-membrane apparatus. Unsaturated hydraulic conductivity K(h) in the range -500< h < -10 cm was determined with the evaporation method. Disturbed soil samples were collected from corresponding locations for soil texture and water content measurement. Soil texture was determined by the pipette method. Water contents at 3, 5 and 15 bar were measured with pressure plate apparatus. Dew point meter was used to measure water contents at lower potentials. Hierarchical neural network PTF implemented in the ROSETTA computer program was used to estimate water retention, saturated and unsaturated hydraulic conductivity based on different levels of input information: texture only, texture and bulk density, and various options for using K_sat as input data. The root mean square error (RMSE) between measured and estimated water contents, saturated and unsaturated hydraulic conductivities for different soil water pressure heads was used to characterize the performance of PTF.

Key words: Soil texture, Bulk density, Pedotransfer functions, Water retention, Hydraulic conductivity