van Genuchten model ITYCL=1

[easternwang]

Hi,

In the water retention van Genuchten model ICL=6, ITYCL=1;

Is the P in the formula the air entry value? I noticed that P=P0(sigma/sigma0). What is sigma here? There are explanations for P0 and sigma0 in the manual as following, but not sigma:

Po (MPa): Measured P at certain temperature
sigma0 (N m-1): Surface tension at temperature in which Po was measured (usually σo=0.072 N/m at 20ºC)

Thank you