First approximations of soil moisture retention curves using the filter-paper method

Relationships between gravimetric soil moisture content (w) and matric potential (φ(m)), and between volumetric soil moisture content (θ(v)) and pressure head (h) were approximated for the unsaturated zone on Long Island, New York. Soil samples were collected from two sites using a hand auger. The soil moisture content was determined using the filter-paper (w(f)) and gravimetric (w) methods, respectively. The w(f) was then used in an empirical equation to estimate φ(m). Each set of φ(m) and w was combined with a straight-line empirical model to obtain a w(φ(m)) relationship. Soil φ(m) was converted to h, and w to the volumetric moisture content θ(v), in order to produce a θ(v)(h) curve. Graphical and statistical comparison showed that the resulting θ(v)(h) curves fell within one order of magnitude of similar curves generated by a more sophisticated non-linear model developed previously. The simplicity and low cost of the filter-paper approach described in this study recommends it for preliminary studies of hydraulic properties in the unsaturated zone. Copyright (C) 2000 John Wiley and Sons, Ltd.