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Comparison of models for indirect estimation of water retention and available water in surface soils

Marcel G. Schaap, Attila Nemes and Martinus T. van Genuchten
Comparison of models for indirect estimation of water retention and available water in surface soils
Vadose Zone Journal (November 2004) 3 (4): 1455-1463

Abstract

Quantitative knowledge of the unsaturated soil hydraulic properties is required in most studies involving water flow and solute transport in the vadose zone. Unfortunately, direct measurement of such properties is often difficult, expensive and time-consuming. Pedotransfer functions (PTFs) offer a means to estimate soil hydraulic properties based on predictors like texture, bulk density, and other soil variables. In this study, we focus on PTFs for water retention and show that systematic errors in five existing PTFs can be reduced by using water content-based objective functions, instead of parameter value-based objective functions. The alternative analysis was accomplished by establishing offset and slope coefficients for each estimated hydraulic parameter. Subsequently we evaluated these and six other PTFs for estimating water retention parameters using the NRCS soils database. A total of 47435 records containing 113970 observed water contents were used to test the PTFs for mean errors and root mean square errors. No overall superior model was found. Models with many calibration parameters or more input variables were not necessarily better than more simple models. All models underestimated water contents, with values ranging from -0.0086 to -0.0279 cm (super 3) cm (super -3) . Average root mean square errors ranged from 0.0687 cm (super 3) cm (super -3) for a PTF that provided textural class average parameters to 0.0315 cm (super 3) cm (super -3) for a model that also used two water retention points as predictors. Available soil water content for vegetation was estimated with errors ranging from 0.058 to 0.080 cm (super 3) cm (super -3) , depending on the model and the definition of available water.


ISSN: 1539-1663
Serial Title: Vadose Zone Journal
Serial Volume: 3
Serial Issue: 4
Title: Comparison of models for indirect estimation of water retention and available water in surface soils
Affiliation: U. S. Department of Agriculture, George E. Brown Jr. Salinity Laboratory, Riverside, CA, United States
Pages: 1455-1463
Published: 200411
Text Language: English
Publisher: Soil Science Society of America, Madison, WI, United States
References: 29
Accession Number: 2005-062206
Categories: SoilsHydrogeology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Accessed on January 25, 2005
Illustration Description: illus. incl. 4 tables
Source Medium: WWW
Secondary Affiliation: Hungarian Academy of Sciences, HUN, Hungary
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200521
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