fitsoilwater4: Self-starting Nls Power Models for Soil Water Retention

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

Description

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.

Usage

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

Arguments

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".

Value

A "nls" object containing the fitted model.

Author(s)

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

References

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.

See Also

fitsoilwater4, soilwater, soilwater2, soilwater3

Examples

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# 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


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