A TWO-LINE APPROXIMATIONOF HYDRAULICCONDUCTIVITYFOR STRUCTUREDSOILS

Laboratory-measured soil hydraulic conductivity and pressure head relationship over the pressure head range of0-120 cm H20 were studied using a two-line regression model. Water content, pressure head and hydraulic conductivity were measured under steady flow conditions. The soils used were one column of packed sandy loam and two undisturbed soil blocks of different pedal structure. The results show that, for all three columns, the two-line regression model fitted the data reasonably well after adjustment for position effects (intercepts). The response pattern shows that the conduc tivity decreases first drastically when tension is increased from 0 cm to 50 cm of H20, but flattens off when tension is beyond this point. It is believed that the difference of the rates of responses in these two tension intervals was due to either soil structure or pore size distribution.