Sindex: The S Index

Description

Function to calculate the S index (Dexter, 2004) for evaluating the soil physical quality based on the Water Retention Curve (van Genuchten, 1980). $$S = - n * (\theta_S - \theta_R) * (1 + 1/m)^{-(1 + m)}$$

Usage

Sindex(theta_R, theta_S, alpha, n, m = 1 - 1/n, vcov = NULL,
	nsim = 999, conf.level = 0.95, graph = TRUE, ...)

Arguments

theta_R

the residual water content.

theta_S

the water content at saturation.

alpha

a scale parameter of the van Genuchten's formula.

a shape parameter in van Genuchten's formula.

a shape parameter in van Genuchten's Formula. Default is $1-1/n$ (Mualem, 1976).

vcov

optional (default is NULL); a variance-covariance matrix of the estimates which is used to perform Monte Carlo simulations of the parameters theta_R, theta_S, alpha and n for building a

nsim

the number of Monte Carlo simulations; default is 999. It is used only if vcov is specified.

conf.level

the confidence level; default is 0.95. It is used only if vcov is specified.

graph

logical; if TRUE (defaul), the soil water retention curve is plotted.

...

further graphical arguments.

Value

A list of
h_ithe modulus of the water potential at the inflection point.
theta_ithe water content at the inflection point.
S.indexthe modulus of the S index.
PhysicalQualityA character indicating the soil physical quality, as proposed by Dexter (2004).
simCIthe simulated confidence interval. It is stored only if vcov is specified.
conf.levelthe confidence level for the simulated confidence interval. It is stored only if vcov is specified.

References

Dexter, A. R. (2004). Soil physical quality Part I. Theory, effects of soil texture, density, and organic matter, and effects on root growth. Geoderma, 120:201-214. Genuchten, M. T. van. (1980). A closed form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal, 44:892-898. Mualem, Y. (1976). A new model for predicting the hydraulic conductivity of unsaturated porous media, Water Resource Research, 12:513-522.

Examples

Run this code

# Dexter (2004, Table 1)
Sindex(0, 0.395, 0.0217, 1.103, xlim = c(0, 1000))
Sindex(0, 0.335, 0.0616, 1.139, xlim = c(0, 1000))
# ...
Sindex(0, 0.226, 0.0671, 1.581, xlim = c(0, 1000))

# End (not run)