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ptfkit.hodnett2002

ptfkit.hodnett2002

Hodnett & Tomasella (2002), tropical-soil regressions for four van Genuchten parameters.

Reference

Hodnett, M. G., & Tomasella, J. (2002). Marked differences between van Genuchten soil water-retention parameters for temperate and tropical soils: A new water-retention pedo-transfer functions developed for tropical soils. Geoderma, 108(3-4), 155-180. DOI: 10.1016/S0016-7061(02)00105-2

Territory

Tropical soils between approximately 25 degrees N and 25 degrees S.

Dataset

The IGBP-DIS tropical-soil dataset contains 771 retained horizons from 249 profiles in 22 countries, split into 492 calibration curves and 279 validation curves.

CLASS DESCRIPTION
Hodnett2002PTFResult

Results returned by the matching PTF.
FUNCTION DESCRIPTION
calc_ptf_hodnett2002

Estimate four van Genuchten water-retention parameters for tropical soils.

Hodnett2002PTFResult

Bases: NamedTuple, Generic[T]

Results returned by the matching PTF.

ATTRIBUTE DESCRIPTION
alpha

Shape parameter of the van Genuchten water-retention model. (kPa^-1)

TYPE: T

n

Shape parameter controlling water-retention curve steepness. (dimensionless)

TYPE: T

theta_s

Saturated volumetric soil water content. (m^3/m^3)

TYPE: T

theta_r

Residual volumetric soil water content. (m^3/m^3)

TYPE: T

Source code in ptfkit/hodnett2002.py 
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class Hodnett2002PTFResult(NamedTuple, Generic[T]):
    """Results returned by the matching PTF.

    Attributes:
        alpha: Shape parameter of the van Genuchten water-retention model. (kPa^-1)
        n: Shape parameter controlling water-retention curve steepness. (dimensionless)
        theta_s: Saturated volumetric soil water content. (m^3/m^3)
        theta_r: Residual volumetric soil water content. (m^3/m^3)

    """

    alpha: T
    n: T
    theta_s: T
    theta_r: T

calc_ptf_hodnett2002 

calc_ptf_hodnett2002(*, sand: float, silt: float, clay: float, organic_carbon: float, bulk_density: float, cation_exchange_capacity: float, ph: float) -> Hodnett2002PTFResult[floating]

calc_ptf_hodnett2002(*, sand: ArrayLike, silt: ArrayLike, clay: ArrayLike, organic_carbon: ArrayLike, bulk_density: ArrayLike, cation_exchange_capacity: ArrayLike, ph: ArrayLike, out: Hodnett2002PTFResult[NDArray[floating]] | None = None) -> Hodnett2002PTFResult[NDArray[floating]]

Estimate four van Genuchten water-retention parameters for tropical soils.

PARAMETER DESCRIPTION
sand

Sand content in the 0.05-2 mm USDA particle-size fraction, expressed as a percentage. (%)

TYPE: float | ArrayLike

silt

Silt content in the 0.002-0.05 mm USDA particle-size fraction, expressed as a percentage. (%)

TYPE: float | ArrayLike

clay

Clay content in the less-than-0.002 mm USDA particle-size fraction, expressed as a percentage. (%)

TYPE: float | ArrayLike

organic_carbon

Soil organic carbon content expressed as a percentage. (%)

TYPE: float | ArrayLike

bulk_density

Soil bulk density. (Mg/m^3)

TYPE: float | ArrayLike

cation_exchange_capacity

Soil cation exchange capacity. (cmol/kg)

TYPE: float | ArrayLike

ph

Soil pH. (dimensionless)

TYPE: float | ArrayLike

out

Optional output arrays for in-place calculation.

TYPE: Hodnett2002PTFResult[NDArray[floating]] | None DEFAULT: None

RETURNS DESCRIPTION
Hodnett2002PTFResult

Results grouped by result attributes.

TYPE: Hodnett2002PTFResult[floating] | Hodnett2002PTFResult[NDArray[floating]]

Models

\(h(\theta)\): van Genuchten model with m = 1 - 1 / n

Notes

Prediction target: Residual and saturated volumetric water content and the alpha and n shape parameters of the van Genuchten water-retention model. The regressions use percentages of sand, silt, clay, and organic carbon, bulk density in Mg/m^3, CEC in cmol/kg, and pH. Table 8 reports the reoptimised Step 3 coefficients used here and states that its displayed values are multiplied by 100; each polynomial is therefore divided by 100 before alpha and n are back-transformed. The fitted ln(alpha) and ln(n) values are back-transformed with the natural exponential, as specified by the paper's use of natural logarithms.

Warning

The paper reports n = 497 when introducing the continuous PTF, but its dataset split gives 492 calibration curves and 279 validation curves, which account for all 771 retained horizons. The extraction treats 497 as a typographical error and records 492 as the calibration-set size. The PTF did not reproduce water-retention curves accurately for soils with bulk density below 0.8 Mg/m^3, most of which were Andosols. The PTF did not reproduce very low alpha values well because high-alpha soils dominated the calibration data; mineralogy and structure were not directly represented.

Source code in ptfkit/hodnett2002.py 
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def calc_ptf_hodnett2002(
    *,
    sand: float | ArrayLike,
    silt: float | ArrayLike,
    clay: float | ArrayLike,
    organic_carbon: float | ArrayLike,
    bulk_density: float | ArrayLike,
    cation_exchange_capacity: float | ArrayLike,
    ph: float | ArrayLike,
    out: Hodnett2002PTFResult[NDArray[floating]] | None = None,
) -> Hodnett2002PTFResult[floating] | Hodnett2002PTFResult[NDArray[floating]]:
    r"""Estimate four van Genuchten water-retention parameters for tropical soils.

    Arguments:
        sand: Sand content in the 0.05-2 mm USDA particle-size fraction, expressed as a percentage.
            (%)
        silt: Silt content in the 0.002-0.05 mm USDA particle-size fraction, expressed as a
            percentage. (%)
        clay: Clay content in the less-than-0.002 mm USDA particle-size fraction, expressed as a
            percentage. (%)
        organic_carbon: Soil organic carbon content expressed as a percentage. (%)
        bulk_density: Soil bulk density. (Mg/m^3)
        cation_exchange_capacity: Soil cation exchange capacity. (cmol/kg)
        ph: Soil pH. (dimensionless)
        out: Optional output arrays for in-place calculation.

    Returns:
        Hodnett2002PTFResult: Results grouped by result attributes.

    Models:
        $h(\theta)$: van Genuchten model with m = 1 - 1 / n

    Notes:
        Prediction target: Residual and saturated volumetric water content and the alpha and n shape
            parameters of the van Genuchten water-retention model.
        The regressions use percentages of sand, silt, clay, and organic carbon, bulk density in
            Mg/m^3, CEC in cmol/kg, and pH.
        Table 8 reports the reoptimised Step 3 coefficients used here and states that its displayed
            values are multiplied by 100; each polynomial is therefore divided by 100 before alpha
            and n are back-transformed.
        The fitted ln(alpha) and ln(n) values are back-transformed with the natural exponential, as
            specified by the paper's use of natural logarithms.

    Warning:
        The paper reports n = 497 when introducing the continuous PTF, but its dataset split gives
            492 calibration curves and 279 validation curves, which account for all 771 retained
            horizons. The extraction treats 497 as a typographical error and records 492 as the
            calibration-set size.
        The PTF did not reproduce water-retention curves accurately for soils with bulk density
            below 0.8 Mg/m^3, most of which were Andosols.
        The PTF did not reproduce very low alpha values well because high-alpha soils dominated the
            calibration data; mineralogy and structure were not directly represented.

    """
    values = _call(
        _calc_ptf_hodnett2002,
        sand,
        silt,
        clay,
        organic_carbon,
        bulk_density,
        cation_exchange_capacity,
        ph,
        out=out,
    )

    return Hodnett2002PTFResult(*values)