| Abstract: | A computer solution to the one-dimensional soil moisture flow equation was used to show how changes in the wet end of the Ψ-θ-K relations affect infiltration and the conductivity-gradient interactions between a crust and the underlying A-horizon of a hypothetic loess soil. Variations in the θ(Ψ) and K(Ψ) relations between 0 and 10 cm water tension caused three-fold differences in simulated steady-state infiltration rates. A crust having many pores that drain at low tensions (i. e., big pores) limited infiltration more than did a crust with the same saturated conductivity, but having few easily drainable pores. With either crust, the infiltration rate was higher when the hydraulic conductivity of the underlying A-horizon was greater over the low suction range. Both crusts limited infiltration more when the underlying A-horizon contained many easily drainable pores than when the A-horizon had only few big pores. Therefore, the wet end of the Ψ-θ-K relation of a tilled surface layer has an important effect upon infiltration, even when overlain by a dense surface crust. The calculations emphasize that estimates of infiltration and runoff are very sensitive to variations in the hydraulic input functions in the low tension range where precise measurements are very difficult. The model results also show how tension gradients and conductivities near the surface can produce infiltration rates that are considerably higher than the saturated conductivity of the crust. |
