fitsoilwater4: Self-starting Nls Power Models for Soil Water Retention
In soilphysics: Soil Physical Analysis

Description Usage Arguments Value Author(s) References See Also Examples

View source: R/fitsoilwater4.R

Function to self start the following nonlinear power models for soil water retention:

θ = \exp(a + b*Bd) ψ^c

(Silva et al., 1994)

θ = a ψ^c

(Ross et al., 1991)

where θ is the soil water content.

fitsoilwater() creates initial estimates (by log-linearization) of the parameters a, b and c and uses them to provide its least-squares estimates through nls.

1	fitsoilwater4(theta, psi, Bd, model = c("Silva", "Ross"))

`theta`	a numeric vector containing values of soil water content.
`psi`	a numeric vector containing values of water potential (Psi).
`Bd`	a numeric vector containing values of dry bulk density.
`model`	a character; the model to be used for calculating the soil water content. It must be one of the two: `"Silva"` (default) or `"Ross"`.

A "nls" object containing the fitted model.

Anderson Rodrigo da Silva <anderson.agro@hotmail.com>

Ross et al. (1991). Equation for extending water-retention curves to dryness. Soil Science Society of America Journal, 55:923-927.

Silva et al. (1994). Characterization of the least limiting water range of soils. Soil Science Society of America Journal, 58:1775-1781.

fitsoilwater4, soilwater, soilwater2, soilwater3

# Example 1
ex1 <- with(skp1994,
    fitsoilwater4(theta = W, psi = h, model = "Ross"))
ex1
summary(ex1)

# Example 2
ex2 <- with(skp1994,
    fitsoilwater4(theta = W, psi = h, Bd = BD, model = "Silva"))
ex2
summary(ex2)

# Not run