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.
fitsoilwater5(theta, x, theta_S, xlab = NULL, ylab = NULL, ...)a numeric vector containing the values of soil water content.
a numeric vector containing the matric potential values.
an offset; a value for the parameter theta_S, the water content at saturation. See details.
a label for the x axis; if is NULL, the label "Matric potential" is used.
a label for the y axis; if is NULL, the label "Soil water content" is used.
further graphical arguments; see par.
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.
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.
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.
# NOT RUN {
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)
# }
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