SSSAJ Grow Your Career with SSSA
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published in Soil Sci Soc Am J 57:26-29 (1993)
© 1993 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
This Article
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Ross, P. J.
Right arrow Articles by Smettem, K. R. J.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Ross, P. J.
Right arrow Articles by Smettem, K. R. J.
GeoRef
Right arrow GeoRef Citation
Agricola
Right arrow Articles by Ross, P. J.
Right arrow Articles by Smettem, K. R. J.

Describing Soil Hydraulic Properties with Sums of Simple Functions

Peter J. Ross* and Keith R. J. Smettem

Division of Soils, CSIRO, PMB, PO Aitkenvale, Townsville, Qld 4814, Australia

*Corresponding author.

ABSTRACT

Simple functions do not adequately describe the hydraulic properties of many field soils, particularly those with substantial macroporosity. By considering the soil pore-size distribution f({psi}) = {Sigma}Ni = 1 {psi}i fi ({psi}) corresponding to the effective saturation S({psi}) = {Sigma}Ni = 1 {psi}i Si({psi}), where {psi} is matric pressure head, the {psi}i are fractions of effective porosity, the Si({psi}) are simple water retention functions in common use, and fi({psi}) = S'i({psi}), we show that the relative hydraulic conductivity according to the Mualem model is Kr({psi}) = Sp[{Sigma}{Sigma}Ni = 1 {psi}i gi({psi})/{Sigma}Ni = 1 {psi}i gi(0)]2, where gi({psi}) = {varepsilon}{psi}-x{psi}–1 fi({psi}) d{psi} and p is a pore interaction index. If the pores of the distributions do not interact, the appropriate relation is K({psi}) = {Sigma}Ni = 1 KsiKri({psi}), where Ksi is the saturated conductivity of distribution i and Kri = Sp[gi({psi})/gi(0)]2. We note that the van Genuchten function S({psi}) = [1 + (–{alpha}{psi})n]–m with the restriction m = 1 – 1/n leads to an infinite slope K'({psi}) at {psi} = 0 unless n ≥ 2, which is unrealistic for field soils if a wide range of matric pressure heads is considered. Hydraulic conductivity near saturation is often expressed as K({psi}) = Ks exp(a{psi}). We introduce the function S({psi}) = (1 – {alpha}{psi}) exp({alpha}{psi}), which gives, according to Mualem's model, a conductivity K({psi}) = Ks(1 – {alpha}{psi})p exp[(p + 2){alpha}{psi}] that approximates Ks exp({alpha}{psi}) near saturation if a = 2{alpha} and is exactly equal if p = 0. As an example, a function using this model for one pore-size distribution and the van Genuchten model for the other was compared with a function using two van Genuchten distributions. The latter gave a slightly improved fit to water content and conductivity data for an aggregated soil.

NOTES

Contribution of CSIRO, Australia. This research was supported in part by the CSIRO Coastal Zone Program.

Received for publication March 16, 1992.


This article has been cited by other articles:


Home page
 Vadose Zone JHome page
T. G. Poulsen, P. Moldrup, S. Yoshikawa, and T. Komatsu
Bimodal Probability Law Model for Unified Description of Water Retention, Air and Water Permeability, and Gas Diffusivity in Variably Saturated Soil
Vadose Zone J., October 3, 2006; 5(4): 1119 - 1128.
[Abstract] [Full Text] [PDF]


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Agronomy Journal Crop Science
Vadose Zone Journal Journal of Plant Registrations
Journal of Natural Resources
and Life Sciences Education		 Journal of
Environmental Quality
Copyright © 1993 by the Soil Science Society of America.