soil texture: Soil texture functions

Description

Functions soil.psi2theta and soil.theta2psi calculate water potentials (psi) and relative water contents (theta) using texture data the formulae of Saxton (1986). Function soil.USDAType returns the USDA type for a given texture. Function soil.vanGenuchtenParams gives parameters for van Genuchten's conductance function for a given texture type (Leij et al. 1996).

Usage

soil.psi2theta(clay, sand, psi)
soil.theta2psi(clay, sand, theta)
soil.USDAType(clay, sand)
soil.vanGenuchtenParams(soilType)

Arguments

clay

Percentage of clay.

sand

Percentage of sand.

psi

Water potential (in MPa).

theta

Relative water content (in percent)

soilType

A string indicating the soil type.

Value

Function soil.psi2theta returns the soil water potential from soil relative water content, and the function soil.theta2psi does the reverse calculation. Function soil.USDAType returns a string. Function soil.vanGenuchtenParams returns a vector with three parameter values.

References

Saxton, K.E., Rawls, W.J., Romberger, J.S., Papendick, R.I., 1986. Estimating generalized soil-water characteristics from texture. Soil Sci. Soc. Am. J. 50, 1031<U+2013>1036.

Leij, F.J., Alves, W.J., Genuchten, M.T. Van, Williams, J.R., 1996. The UNSODA Unsaturated Soil Hydraulic Database User<U+2019>s Manual Version 1.0.

Examples

Run this code

# NOT RUN {
type = soil.USDAType(clay=10, sand=70)
soil.vanGenuchtenParams(type)

psi = seq(0, -6000, by=-100)
plot(psi, lapply(as.list(psi), FUN=soil.psi2theta, clay=70, sand=10), 
     type="l", ylim=c(0,0.5), ylab="Theta")
lines(psi, lapply(as.list(psi), FUN=soil.psi2theta, clay=10, sand=70), lty=2)

# }