This study discusses the selection of
parametric models of the moisture retention characteristic MRC as nonlinear
regression models from a mathematical and statistical viewpoint. Simulation
studies and some measures of nonlinearity are given. A comparison is introduced
between the used famous models of the moisture retention characteristic
(van Genuchten and King) which are presented early and their variants.
Following the considered simulation study and the used measures of nonlinearity
in nonlinear regression the author find that although a variant of van
Genuchten model with four parameters is an optimal model but it has a
strong nonlinear parameter. Moreover, a possible appropriate reparametrization
with respect to this nonlinear parameter is proposed.