<ptfkit/hodnett2002.h>¶
#include <ptfkit/hodnett2002.h>
Hodnett & Tomasella (2002), tropical-soil regressions for four van Genuchten parameters.
Source¶
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
Scope¶
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.
hodnett2002_ptf_result¶
typedef struct {
double alpha;
double n;
double theta_s;
double theta_r;
} hodnett2002_ptf_result;
| Field | Description |
|---|---|
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) |
Functions¶
calc_ptf_hodnett2002¶
Estimate four van Genuchten water-retention parameters for tropical soils.
static inline hodnett2002_ptf_result calc_ptf_hodnett2002(double sand, double silt, double clay, double organic_carbon, double bulk_density, double cation_exchange_capacity, double ph);
Parameters¶
| Name | Direction | Description |
|---|---|---|
sand | in | Sand content in the 0.05-2 mm USDA particle-size fraction, expressed as a percentage. (%) |
silt | in | Silt content in the 0.002-0.05 mm USDA particle-size fraction, expressed as a percentage. (%) |
clay | in | Clay content in the less-than-0.002 mm USDA particle-size fraction, expressed as a percentage. (%) |
organic_carbon | in | Soil organic carbon content expressed as a percentage. (%) |
bulk_density | in | Soil bulk density. (Mg/m^3) |
cation_exchange_capacity | in | Soil cation exchange capacity. (cmol/kg) |
ph | in | Soil pH. (dimensionless) |
Returns¶
A hodnett2002_ptf_result value.
Note
The regressions use percentages of sand, silt, clay, and organic carbon, bulk density in Mg/m^3, CEC in cmol/kg, and pH.
Note
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.
Note
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.
Warning
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.
Warning
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.