An Alert Regarding a Common Misinterpretation of the Van Genuchten α Parameter

Abstract

Among the equations available to describe the relation between matric potential and soil water content, the soil water retention function, the most commonly used is the equation proposed by Van Genuchten in his 1980 landmark paper. In soil physics literature, especially in Brazil, several authors relate the inverse of the Van Genuchten parameter α to the air-entry pressure. This study aimed to show this common interpretation to be erroneous, as 1/α corresponds to water contents lower than saturation. The deviation depends on the m parameter. In fact, α is merely a scaling parameter relative to the matric potential axis. Recognizing this mathematical fact may improve the interpretation of soil hydraulic properties based on water retention parameters.

No‐till cover crop effects on the hydro‐physical properties of a silt loam

“…The vG α parameter is a scaling parameter relative to the matric potential axis of the soil water retention curve (van Lier & Pinheiro, 2018). As such, the higher vG α parameter under CC compared with NC management in the current study suggests that CC management can increase the amount of water retained in the soil at measured soil water pressures.…”

An Unsaturated Hydraulic Conductivity Model Based on the Capillary Bundle Model, the Brooks‐Corey Model and Waxman‐Smits Model

“…The model parameters can be determined by fitting the van Genuchten (1980) model to the θ ( ψ ) measurements. The van Genuchten (1980) model describes the θ ( ψ ) curve as, $$${S}_{\mathrm{e}}=\frac{\theta -{\theta }_{\mathrm{r}}}{{\theta }_{\mathrm{s}}-{\theta }_{\mathrm{r}}}={\left[\frac{1}{1+{(\alpha \vert \psi \vert )}^{p}}\right]}^{(1-1/p)}$$$ where α (>0, cm −1 ) is a scale parameter relative to the matric potential axis (van Lier & Pinheiro, 2018).…”