Saxton and Rawls (2006), soil water characteristics from texture and organic matter.¶
Source¶
Saxton, K. E., & Rawls, W. J. (2006). Soil water characteristic estimates by texture and organic matter for hydrologic solutions. Soil Science Society of America Journal, 70(5), 1569-1578.
Scope¶
Territory: United States
Dataset: 1,722 mineral-soil A-horizon samples retained from the USDA/NRCS National Soil Characterization database after exclusions from 2,149 samples.
Functions¶
calc_ptf_saxton2006¶
Estimate soil water characteristics from sand, clay, and organic matter.
Status: implemented
Prediction target: Water contents at 1500, 33, and 0 kPa, plant-available water, air-entry tension, retention coefficients, normal density, and saturated hydraulic conductivity.
Models: \(h(\theta)\) — Campbell power function with a linear wet-range segment; \(k(h)\) — Campbell unsaturated conductivity model
Inputs¶
| Name | Type | Unit | Domain | Description |
|---|---|---|---|---|
sand | number | g/g | 0 <= value <= 1 | Sand mass fraction of the fine-earth soil. |
clay | number | g/g | 0 <= value <= 0.60 | Clay mass fraction of the fine-earth soil. |
organic_matter | number | % mass | 0 <= value <= 8 | Organic matter content on a mass percentage basis. |
Outputs¶
| Name | Unit | Domain | Description |
|---|---|---|---|
theta_1500 | m^3/m^3 | value > 0 | Volumetric water content at 1500 kPa matric tension. |
theta_33 | m^3/m^3 | value > 0 | Volumetric water content at 33 kPa matric tension. |
theta_s | m^3/m^3 | value > 0 | Saturated volumetric water content at normal density. |
plant_available_water | m^3/m^3 | value >= 0 | Difference between the 33 and 1500 kPa water contents. |
air_entry_tension | kPa | value > 0 | Air-entry or bubbling-pressure tension. |
retention_a | kPa | value > 0 | Coefficient A of the dry-range moisture-tension curve. |
retention_b | dimensionless | value > 0 | Exponent B of the dry-range moisture-tension curve. |
conductivity_lambda | dimensionless | value > 0 | Inverse of retention exponent B. |
saturated_conductivity | mm/h | value >= 0 | Saturated hydraulic conductivity of the matric soil. |
normal_density | g/cm^3 | value > 0 | Normal dry bulk density assuming particle density 2.65 g/cm^3. |
Note
Sand and clay are decimal mass fractions, while organic matter is a percentage.
Note
The 1500 and 33 kPa values are also termed wilting point and field capacity.
Warning
Do not apply the regression above 8% organic matter or 60% clay.
Warning
Sand and clay fractions must describe one soil and therefore must sum to at most 1.
Warning
These statistical-average estimates should be calibrated to local measurements when available.
calc_density_adjustment_saxton2006¶
Adjust Saxton and Rawls water characteristics for soil density.
Status: implemented
Prediction target: Density-adjusted saturation and 33 kPa water contents.
Models: \(h(\theta)\) — Density adjustment to the point estimates
Inputs¶
| Name | Type | Unit | Domain | Description |
|---|---|---|---|---|
normal_density | number | g/cm^3 | value > 0 | Normal dry bulk density estimated by the base model. |
theta_s | number | m^3/m^3 | value > 0 | Saturated water content at normal density. |
theta_33 | number | m^3/m^3 | value > 0 | Water content at 33 kPa and normal density. |
density_factor | number | dimensionless | 0.9 <= value <= 1.3 | Multiplicative adjustment to normal density. |
Outputs¶
| Name | Unit | Domain | Description |
|---|---|---|---|
adjusted_density | g/cm^3 | value > 0 | Density after applying the density factor. |
adjusted_theta_s | m^3/m^3 | value > 0 | Saturated water content after the density adjustment. |
adjusted_theta_33 | m^3/m^3 | value > 0 | Water content at 33 kPa after the density adjustment. |
adjusted_theta_s_minus_33 | m^3/m^3 | value >= 0.005 | Density-adjusted difference between saturation and 33 kPa. |
Note
The source limits the saturation-minus-33 kPa difference to at least 0.005 m^3/m^3.
Warning
The source recommends density factors only from 0.9 to 1.3.
calc_tension_dry_saxton2006¶
Estimate matric tension in the 1500 to 33 kPa segment.
Status: implemented
Prediction target: Matric tension for water content between theta_1500 and theta_33.
Models: \(h(\theta)\) — Campbell power function
Inputs¶
| Name | Type | Unit | Domain | Description |
|---|---|---|---|---|
theta | number | m^3/m^3 | theta_1500 <= value <= theta_33 | Volumetric water content. |
theta_1500 | number | m^3/m^3 | value > 0 | Volumetric water content at 1500 kPa. |
theta_33 | number | m^3/m^3 | value > theta_1500 | Volumetric water content at 33 kPa. |
Outputs¶
| Name | Unit | Domain | Description |
|---|---|---|---|
tension | kPa | 33 <= value <= 1500 | Matric tension at the supplied water content. |
Warning
Use only for the 1500 to 33 kPa segment defined by the source.
calc_tension_wet_saxton2006¶
Estimate matric tension in the 33 kPa to air-entry segment.
Status: implemented
Prediction target: Matric tension for water content between theta_33 and theta_s.
Models: \(h(\theta)\) — Linear wet-range segment
Inputs¶
| Name | Type | Unit | Domain | Description |
|---|---|---|---|---|
theta | number | m^3/m^3 | theta_33 <= value <= theta_s | Volumetric water content. |
theta_33 | number | m^3/m^3 | value > 0 | Volumetric water content at 33 kPa. |
theta_s | number | m^3/m^3 | value > theta_33 | Saturated volumetric water content. |
air_entry_tension | number | kPa | 0 <= value < 33 | Air-entry tension estimated by the base model. |
Outputs¶
| Name | Unit | Domain | Description |
|---|---|---|---|
tension | kPa | air_entry_tension <= value <= 33 | Matric tension at the supplied water content. |
Note
At tensions below air entry, Equation 13 fixes water content at theta_s.
Warning
Use only for the 33 kPa to air-entry segment defined by the source.
calc_conductivity_saxton2006¶
Estimate unsaturated hydraulic conductivity from water content.
Status: implemented
Prediction target: Unsaturated hydraulic conductivity of the matric soil.
Models: \(k(h)\) — Campbell unsaturated conductivity model
Inputs¶
| Name | Type | Unit | Domain | Description |
|---|---|---|---|---|
theta | number | m^3/m^3 | 0 < value <= theta_s | Volumetric water content. |
theta_s | number | m^3/m^3 | value > 0 | Saturated volumetric water content. |
saturated_conductivity | number | mm/h | value >= 0 | Saturated hydraulic conductivity of the matric soil. |
conductivity_lambda | number | dimensionless | value > 0 | Inverse of retention exponent B. |
Outputs¶
| Name | Unit | Domain | Description |
|---|---|---|---|
conductivity | mm/h | value >= 0 | Unsaturated hydraulic conductivity at the supplied water content. |
Warning
The equation does not include residual water content.
calc_gravel_adjustment_saxton2006¶
Adjust matric-soil properties for gravel content.
Status: implemented
Prediction target: Gravel volume, bulk density, available water, and saturated conductivity.
Models: \(h(\theta)\) — Gravel reduction of plant-available water; \(k(h)\) — Peck-Watson conductivity reduction
Inputs¶
| Name | Type | Unit | Domain | Description |
|---|---|---|---|---|
gravel_weight_fraction | number | g/g | 0 <= value < 1 | Gravel mass fraction of the bulk soil. |
matric_density | number | g/cm^3 | 0 < value <= 2.65 | Dry bulk density of the fine-earth matric soil. |
plant_available_water | number | m^3/m^3 | value >= 0 | Plant-available water of the matric soil. |
saturated_conductivity | number | mm/h | value >= 0 | Saturated hydraulic conductivity of the matric soil. |
Outputs¶
| Name | Unit | Domain | Description |
|---|---|---|---|
gravel_volume_fraction | m^3/m^3 | 0 <= value < 1 | Gravel volume fraction of the bulk soil. |
bulk_density | g/cm^3 | value > 0 | Dry bulk density of matric soil plus gravel. |
bulk_plant_available_water | m^3/m^3 | value >= 0 | Plant-available water on a bulk-soil volume basis. |
bulk_saturated_conductivity | mm/h | value >= 0 | Saturated conductivity after the gravel reduction. |
Note
Gravel comprises particles larger than 2 mm.
Note
Gravel density is fixed at 2.65 g/cm^3 in the source equations.
Warning
The conductivity correction does not represent extra macropores sometimes found in gravelly soils.
calc_osmotic_potential_saxton2006¶
Estimate saturated and moisture-adjusted osmotic potential.
Status: implemented
Prediction target: Osmotic potential from saturated-extract electrical conductivity.
Models: \(h(\theta)\) — Matric-plus-osmotic tension adjustment
Inputs¶
| Name | Type | Unit | Domain | Description |
|---|---|---|---|---|
electrical_conductivity | number | dS/m | value >= 0 | Electrical conductivity of a saturated soil extract. |
theta | number | m^3/m^3 | 0 < value <= theta_s | Current volumetric water content. |
theta_s | number | m^3/m^3 | value > 0 | Saturated volumetric water content. |
Outputs¶
| Name | Unit | Domain | Description |
|---|---|---|---|
saturated_osmotic_potential | kPa | value >= 0 | Osmotic potential at saturation. |
osmotic_potential | kPa | value >= 0 | Osmotic potential at the supplied water content. |
Note
The moisture adjustment assumes dissolved salt quantity remains near constant as water content falls.
Warning
Precipitation, bonding, ionic nutrition, and toxicity can modify actual salinity effects.