iwc {soilphysics}

Integral Water Capacity (IWC)

Description

Quantifying the soil water availability for plants through the IWC approach. The theory was based on the work of Groenevelt et al. (2001), Groenevelt et al. (2004) and Asgarzadeh et al. (2014), using the van Genuchten-Mualem Model for estimation of the water retention curve and a simple power model for penetration resistance. The salinity effect on soil available water is also implemented here, according to Groenevelt et al. (2004).

Usage

iwc(theta_R, theta_S, alpha, n, a, b, hos = 0, 
    graph = TRUE, 
    xlab = "Matric head (cm)", 
    ylab = expression(cm^-1), 
    xlim1 = NULL,
    xlim2 = NULL, 
    xlim3 = NULL,
    ylim1 = NULL, 
    ylim2 = NULL, 
    ylim3 = NULL,
    col12 = c("black", "blue", "red"),
    col3 = c("orange", "black"),
    lty12 = c(1, 3, 2), 
    lty3 = c(2, 1), ...)

Arguments

theta_R

the residual water content (m^3~m{-3}); a numeric parameter from van Genuchten's model; see details.

theta_S

the water content at saturation (m^3~m{-3}); a numeric parameter from van Genuchten's model; see details.

alpha

a scale parameter from van Genuchten's model; see details.

n

a shape parameter from van Genuchten's model; see details.

a

a parameter of the soil penetration resistance model; see details.

b

a parameter of the soil penetration resistance model; see details.

hos

optional; the value of osmotic head of the saturated soil extract (cm). Used only if one is concerned about the salinity effects on the water available for plants. Default is zero. See Groenevelt et al. (2004) for more details.

graph

logical; if TRUE (default), graphics for both dry and wet range are built.

xlab

a label for x-axis.

ylab

a label for y-axis.

xlim1, xlim2, xlim3

the x limits (x1, x2) of each plot. See plot.default.

ylim1, ylim2, ylim3

the y limits (y1, y2) of each plot. See plot.default.

col12

a vector of length 3 containing the color of each line of the first two plots. See par.

col3

a vector of length 2 containing the color of each line of the third plot. See par.

lty12

a vector of length 3 containing the line types for the first two plots. See par.

lty3

a vector of length 2 containing the line types for the third plot. See par.

...

further graphical parameters. See par.

Details

The parameters of the van Genuchten-Mualem Model can be estimated through the function fitsoilwater(). The soil penetration resistance model is given by: PR = a*h^b, where h is the soil water content and a and b are the fitting parameters.

Value

A table containing each integration of IWC (integral water capacity, in m/m) and EI (integral energy calculation, in J/kg).

Author(s)

Anderson Rodrigo da Silva <[e-mail]>

References

Asgarzadeh, H.; Mosaddeghi, M.R.; Nikbakht, A.M. (2014) SAWCal: A user-friendly program for calculating soil available water quantities and physical quality indices. Computers and Electronics in Agriculture, 109:86–93.

Groenevelt, P.H.; Grant, C.D.; Semetsa, S. (2001) A new procedure to determine soil water availability. Australian Journal Soil Research, 39:577–598.

Groenevelt, P.H., Grant, C.D., Murray, R.S. (2004) On water availability in saline soils. Australian Journal Soil Research, 42:833–840.

See Also

soilwater, fitsoilwater, llwr

Examples

# example 1 (Fig 1b, Asgarzadeh et al., 2014)
iwc(theta_R = 0.0160, theta_S = 0.4828, alpha = 0.0471, n = 1.2982, 
	a = 0.2038, b = 0.2558, graph = TRUE) 

# example 2 (Table 1, Asgarzadeh et al., 2014)
iwc(theta_R = 0.166, theta_S = 0.569, alpha = 0.029, n = 1.308, 
	a = 0.203, b = 0.256, graph = TRUE) 

# example 3: evaluating the salinity effect
iwc(theta_R = 0.166, theta_S = 0.569, alpha = 0.029, n = 1.308, 
	a = 0.203, b = 0.256, hos = 200, graph = TRUE)

# End (Not run)