Sindex: The S Index

In arsilva87/soilphysics: Soil Physical Analysis

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 * (θ_S - θ_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.
n	a shape parameter in van Genuchten's formula.
m	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 simulated confidence interval of the S index (in modulus).
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_i	the modulus of the water potential at the inflection point.
theta_i	the water content at the inflection point.
S.index	the modulus of the S index.
PhysicalQuality	A character indicating the soil physical quality, as proposed by Dexter (2004).
simCI	the simulated confidence interval. It is stored only if vcov is specified.
conf.level	the confidence level for the simulated confidence interval. It is stored only if vcov is specified.

Author(s)

Anderson Rodrigo da Silva <[e-mail]>

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.

See Also

soilwater, fitsoilwater

Examples

# 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)

arsilva87/soilphysics documentation built on July 30, 2022, 8:46 p.m.