soilphysics (version 2.1)

soilwater5: Soil Water Retention, based on the modified van Genuchten's formula

Description

Function to calculate the soil water content based on the modified van Genuchten's formula, as suggested by Pierson and Mulla (1989): $$\theta = \theta_R + (\theta_S - \theta_R)(1 + (\alpha x)^n)^{-m} + b_0 + b_1 x + b_2 * x^2$$

Usage

soilwater5(x, theta_R, theta_S, alpha, n, m = 1 - 1/n, b0, b1, b2)

Arguments

x

the matric potential.

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).

b0

a parameter added to the van Ganuchten's formula.

b1

a parameter added to the van Ganuchten's formula.

b2

a parameter (of quadratic term) added to the van Ganuchten's formula.

Value

• The the soil water content or the saturation index (a value between 0 and 1).

References

Pierson, F.B.; Mulla, D.J. (1989) An Improved Method for Measuring Aggregate Stability of a Weakly Aggregated Loessial Soil. Soil Sci. Soc. Am. J., 53:1825--1831.

See Also

fitsoilwater5

Examples

soilwater5(x = 20, theta_R = 0.2735, theta_S = 0.478, alpha = 0.1029, 
	n = 9.45, b0 = 0.2278, b1 = -0.0165, b2 = 0.000248)
curve(soilwater5(x, theta_R = 0.2735, theta_S = 0.478, alpha = 0.1029, 
	n = 9.45, b0 = 0.2278, b1 = -0.0165, b2 = 0.000248), 
	from = 0, to = 40,
	ylab = "Water content",
	xlab = "Matric potential")

# End (Not run)