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Look up Van Genuchten parameters from the Minidisk reference table

Source: R/infiltration_vg_params.R
infiltration_vg_params.Rd

Appends Van Genuchten shape parameters (n, α) and the tabulated A value to each row of data by matching texture class and suction level against the built-in minidisk_vg_params lookup table (Decagon Devices, Inc., 2005).

Usage

infiltration_vg_params(data, texture, suction)

Arguments

data

A data frame or tibble.

texture

Bare column name or character scalar; USDA texture class (lowercase, e.g. "clay loam"). Must match one of the 12 classes in minidisk_vg_params.

suction

Bare column name, numeric scalar, or character scalar (e.g. "2cm"); suction level in cm. Must match one of 0.5, 1, 2, 3, 4, 5, 6, or 7 cm for full lookup. Pass 0 to retrieve only shape parameters.

Value

The input data as a tibble with three additional columns:

  • .n — Van Genuchten n parameter (dimensionless, > 1)

  • .alpha — Van Genuchten α parameter (1/cm)

  • .A — tabulated A value for a 2.25 cm disc; NA when suction is 0

Details

The lookup table covers 12 USDA texture classes and suction levels of 0.5, 1, 2, 3, 4, 5, 6, and 7 cm (all for a disc radius of 2.25 cm). For the BeerKan experiment (null pressure head), pass suction = 0 — the function will return the tabulated shape parameters (n, α) while setting .A to NA, as A is not defined at zero suction in the Decagon table.

References

Decagon Devices, Inc. (2005). Mini Disk Infiltrometer User's Manual.

See also

minidisk_vg_params for the full lookup table, parameter_A_zhang() to compute A analytically from n and α.

Examples

library(tibble)

soils <- tibble(
  site    = c("A", "B"),
  texture = c("sandy loam", "clay loam"),
  suction = c(4, 2)
)
infiltration_vg_params(soils, texture = texture, suction = suction)
#> # A tibble: 2 × 6
#>   site  texture    suction    .n .alpha    .A
#>   <chr> <chr>        <dbl> <dbl>  <dbl> <dbl>
#> 1 A     sandy loam       4  1.89  0.075  3.95
#> 2 B     clay loam        2  1.31  0.019  6.64

# Scalar suction
infiltration_vg_params(soils, texture = texture, suction = 3)
#> # A tibble: 2 × 6
#>   site  texture    suction    .n .alpha    .A
#>   <chr> <chr>        <dbl> <dbl>  <dbl> <dbl>
#> 1 A     sandy loam       4  1.89  0.075  3.93
#> 2 B     clay loam        2  1.31  0.019  7.23

# Character suction string
soils2 <- tibble(texture = "loam", suction = "2cm")
infiltration_vg_params(soils2, texture = texture, suction = suction)
#> # A tibble: 1 × 5
#>   texture suction    .n .alpha    .A
#>   <chr>   <chr>   <dbl>  <dbl> <dbl>
#> 1 loam    2cm      1.56  0.036  6.27

# For BeerKan: retrieve shape params only (A is NA at suction = 0)
beerkan_meta <- tibble(texture = "sandy loam", theta_s = 0.45, theta_i = 0.1)
infiltration_vg_params(beerkan_meta, texture = texture, suction = 0)
#> # A tibble: 1 × 6
#>   texture    theta_s theta_i    .n .alpha    .A
#>   <chr>        <dbl>   <dbl> <dbl>  <dbl> <dbl>
#> 1 sandy loam    0.45     0.1  1.89  0.075    NA