Compute the Zhang (1997) A parameter for Minidisk analysis — parameter_A

Calculates the shape parameter A from the analytical expression proposed by Zhang (1997), using Van Genuchten parameters n and α together with the applied suction and disc radius:

Usage

parameter_A_zhang(data, n, alpha, suction, radius = 2.25)

Arguments

data: A data frame or tibble.
n: Van Genuchten n parameter (dimensionless, must be > 1). Bare column name or scalar.
alpha: Van Genuchten α parameter (1/cm, must be > 0). Bare column name or scalar.
suction: Applied suction in cm (absolute value used internally). Bare column name or scalar.
radius: Disc radius in cm. Defaults to 2.25 (Minidisk standard).

Value

The input data as a tibble with one additional column .A.

Details

$$A = \frac{11.65 \cdot (n^{0.1} - 1) \cdot \exp\!\bigl(B(n) \cdot (n - 1.9) \cdot \alpha \cdot |h|\bigr)} {(\alpha \cdot r_0)^{0.91}}$$

where $B(n) = 7.5$ if $n < 1.9$ and $B(n) = 2.92$ otherwise.

All column arguments accept bare column names or scalar numeric values, following the tidy evaluation convention of the TidySoils ecosystem.

References

Zhang, R. (1997). Determination of soil sorptivity and hydraulic conductivity from the disk infiltrometer. Soil Science Society of America Journal, 61(4), 1024–1030. https://doi.org/10.2136/sssaj1997.03615995006100060008x

Examples

library(tibble)

soils <- tibble(
  site   = c("A", "B"),
  n      = c(1.89, 1.56),
  alpha  = c(0.075, 0.036),
  suction = c(4, 2)
)

# Using bare column names
parameter_A_zhang(soils, n = n, alpha = alpha, suction = suction)
#> # A tibble: 2 × 5
#>   site      n alpha suction    .A
#>   <chr> <dbl> <dbl>   <dbl> <dbl>
#> 1 A      1.89 0.075       4  3.78
#> 2 B      1.56 0.036       2  4.34

# Scalar suction, column n and alpha
parameter_A_zhang(soils, n = n, alpha = alpha, suction = 3)
#> # A tibble: 2 × 5
#>   site      n alpha suction    .A
#>   <chr> <dbl> <dbl>   <dbl> <dbl>
#> 1 A      1.89 0.075       4  3.80
#> 2 B      1.56 0.036       2  3.96

# Non-standard disc radius
parameter_A_zhang(soils, n = n, alpha = alpha, suction = suction, radius = 3)
#> # A tibble: 2 × 5
#>   site      n alpha suction    .A
#>   <chr> <dbl> <dbl>   <dbl> <dbl>
#> 1 A      1.89 0.075       4  2.91
#> 2 B      1.56 0.036       2  3.34