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Scientia Agricola

On-line version ISSN 1678-992X

Sci. agric. vol.57 n.1 Piracicaba Jan./Mar. 2000

http://dx.doi.org/10.1590/S0103-90162000000100031 

Nota

Software to model soil water retention curves (SWRC, version 2.00)

 

Durval Dourado-Neto1,5*; Donald R. Nielsen2; Jan W. Hopmans2; Klaus Reichardt3,4,5; Osny Oliveira Santos Bacchi3,5
1Depto. de Produção Vegetal - USP/ESALQ, C.P. 9 - CEP: 13418-900 - Piracicaba, SP.
2Department of Land, Air and Water Resources. University of California. Davis, CA. 95616.
3Laboratório de Física de Solos - USP/CENA, C.P. 96 - CEP: 13400-970 - Piracicaba, SP.
4Depto. de Ciências Exatas - USP/ESALQ, C.P. 9 - CEP: 13418-900 - Piracicaba, SP.
5Bolsista CNPq.
*Corresponding author dourado@carpa.ciagri.usp.br

 

 

ABSTRACT: A software for the adjustment of soil water retention curves (SWRC) is presented, using twelve models found in the literature.
Key words: soil matric potential, soil water content, retention

 

Programa computacional para modelagem de curvas de retenção de água no solo (SWRC, versão 2.00)

RESUMO: Um programa computacional é apresentado para o ajuste de curvas de retenção de água (SWRC), utilizando doze modelos encontrados na literatura.
Palavras-chave: potencial mátrico, umidade do solo, retenção

 

 

INTRODUCTION

The SWRC software was developed with the objective of estimating the empirical parameters of the soil-water retention curve, for different models, using the least-squares method and the general iterative method of Newton-Raphson. The software permits the following options: (i) estimation of initial values by anamorphosis and manual procedures, (ii) estimation of Van Genuchten’s (1980) parameter m for two different conditions: independent and dependent, with the dependent case having the restrictions described by Mualem’s (m=1-1/n) model or Burdine’s (m=1-2/n) model (Van Genuchten, 1980), and (iii) the estimation of residual and saturated soil water content by (a) a fixed value procedure (measured or any value fixed by the user), (b) by regression (with and without restriction), or (c) by an extrapolation method (Jong van Lier & Dourado-Neto, 1993). This software can be useful for routine analysis of soil water retention data.

 

MATERIAL AND METHODS

The SWRC software, version 2.00, was developed in VISUAL BASIC 6.0 for the Windows environment (IBM or compatible) with twelve models for soil-water retention curves (TABLES 1 and 2). The input file format is ASCII, the first column refering to the matric potential, and the following columns refering to soil water content. The output permits an approximated r2-value, as an indication of the explained variance by the fitted model, the residual sum of squares to compare different models, and the analysis of variance for nonlinear regression. The F-test (Campbell, 1974) is used to verify the fitting of the selected model.

 

a30t1.gif (24211 bytes)

 

 

a30t2.gif (20516 bytes)

 

Estimated values of empirical parameters for each model, and graphs of the soil-water retention curve, relative hydraulic conductivity, water capacity and relative soil-water diffusivity are outputs of the SWRC software.

There are two different options to compute all empirical parameters: (i) anamorphosis procedure, and (ii) iterative method of Newton-Raphson.

 

RESULT

The result is the SWRC software, available through contact with the first author: dourado@carpa.ciagri.usp.br.

 

REFERENCES

BROOKS, R.H.; COREY, A.T. Hydraulic properties of porous media. Fort Collins, Colorado State University, 1964. (Hydrology Paper, 3).

CAMPBELL, G.S. A simple method for determining unsaturated conductivity from moisture retention data. Soil Science, v.117, p.311-314. 1974.

DRIESSEN, P.M. Land use system analysis. Wageningen, 1986.

FARREL, D.A.; LARSON, W.E. Modeling the pore structure of porous media. Water Resources Research, v.8, p.699-706, 1972.

GARDNER, W.R. Some steady state solutions of unsaturated moisture flow equations with application to evaporation from water table. Soil Science, v.85, p.228-232, 1958.

JONG VAN LIER, Q. de; DOURADO-NETO, D. Valores extremos de umidade do solo referentes ao modelo de van Genuchten. Revista Brasileira de Ciência do Solo, v.17, p.325-329,1993.

LIBARDI, P.L.; REICHARDT, K.; NASCIMENTO-FILHO, V. F. Análise da redistribuição da água visando a condutividade hidráulica do solo. Energia Nuclear & Agricultura, v.1, p.108-122, 1979.

ROGOWSKI, A.S. Watershed physics: model of soil moisture characteristics. Water Resources Research, v.7, p.1575-1582. 1971.

SIMMONS, C.S.; NIELSEN, D.R.; BIGGAR, J.W. Scaling of field-measured soil water properties. Hilgardia, v.47, p.77-173, 1979.

VAN GENUCHTEN, M.T. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal, v.44, p.892-898, 1980.

VISSER, W.C. Progress in the knowledge about the effect of soil moisture content on plant production. Wageningen: Institute for Land and Water Management Research, 1966. (Technical Bulletin, 45)

 

 

Received September 23, 1999

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