fitsoilwater5: Interactive Estimation of the Modified van Genuchten's Model...

In soilphysics: Soil Physical Analysis

Description

An interactive graphical adjustment of the soil water retention curve via the van Genuchten's formula, modified by Pierson and Mulla (1989). The nonlinear least-squares estimates can be achieved taking the graphical initial values. It may be useful to estimate the parameters needed in the high-energy-moisture-characteristics (HEMC) method, which is used to analyze the aggregate stability.

Usage

fitsoilwater5(theta, x, theta_S, xlab = NULL, ylab = NULL, ...)

Arguments

theta	a numeric vector containing the values of soil water content.
x	a numeric vector containing the matric potential values.
theta_S	an offset; a value for the parameter theta_S, the water content at saturation. See details.
xlab	a label for the x axis; if is NULL, the label "Matric potential" is used.
ylab	a label for the y axis; if is NULL, the label "Soil water content" is used.
...	further graphical arguments; see par.

Details

The parameter theta_S must be passed as an argument. It is recommended to consider it as the highest water content value in the data set or the water content at saturation.

Value

A plot of theta versus x and the curve of the current fitted model according to the adjusted parameters in an external interactive panel. Pressing the button "NLS estimates" a nls summary of the fitted model is printed on console whether convergence is achieved, otherwise a warning box of "No convergence" is shown.

Author(s)

Anderson Rodrigo da Silva <[e-mail]>

References

Pierson, F.B.; Mulla, D.J. (1989) An Improved Method for Measuring Aggregate Stability of a Weakly Aggregated Loessial Soil. Soil Sci. Soc. Am. J., 53:1825–1831.

See Also

nls, soilwater5

Examples

h <- seq(0.1, 40, by = 2)
w <- c(0.735, 0.668, 0.635, 0.612, 0.559, 0.462, 0.369, 0.319, 0.296, 0.282, 
	0.269, 0.256, 0.249, 0.246, 0.239, 0.236, 0.229, 0.229, 0.226, 0.222)
plot(w ~ h)

# suggestions of starting values: thetaR = 0.35, alpha = 0.1, n = 10, 
# b0 = 0.02, b1 = -0.0057, b2 = 0.00004 (Not run)

fitsoilwater5(theta = w, x = h, theta_S = 0.70)

# End (Not run)

soilphysics documentation built on Jan. 13, 2021, 7:06 p.m.