Self-starting Nls Power Models for Soil Water Retention
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.
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: |
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.
data(skp1994)
# 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 runPlease choose more modern alternatives, such as Google Chrome or Mozilla Firefox.