Skip to content

Soil

Soil physics related functions.

get_air_entry_pot(field_capacity, sat_water_content, b_value)

Return air entry potential.

field_capacity: water content at field capacity (m3/m3)
sat_water_content: saturated water content
b_value: soil parameter

References:

Kemanian, A.R., Stockle, C.O., 2010. C-Farm: A simple model to evaluate the
 carbon balance of soil profiles. Eur. J. Agron. 32, 22-29.

Examples:

>>> get_air_entry_pot(.08,0.5,4.33)
-0.0118
Source code in environmental_biophysics/soil.py 
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
def get_air_entry_pot(
    field_capacity: float | NDArray,
    sat_water_content: float | NDArray,
    b_value: float | NDArray,
) -> float:
    """Return air entry potential.

    Args:
    ----
        field_capacity: water content at field capacity (m3/m3)
        sat_water_content: saturated water content
        b_value: soil parameter

    References:
    ----------
        Kemanian, A.R., Stockle, C.O., 2010. C-Farm: A simple model to evaluate the
         carbon balance of soil profiles. Eur. J. Agron. 32, 22-29.

    Examples:
    --------
        >>> get_air_entry_pot(.08,0.5,4.33)
        -0.0118

    """
    result = -33 * (field_capacity / sat_water_content) ** b_value
    return round(result, 4)

get_b_value(water_content_33_j_kg, water_content_1500_j_kg)

Return b soil parameter.

water_content_33_j_kg: water content at -33 J/kg
water_content_1500_j_kg: water content at -1500 J/kg

References:

Saxton, K.E., Rawls, W.J., 2006. Soil water characteristic estimates by texture
 and organic matter for hydrologic solutions. Soil Sci. Soc. Am. J. 70,
 1569-1578.

Examples:

>>> get_b_value(0.08, 0.03)
3.89
Source code in environmental_biophysics/soil.py 
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
def get_b_value(
    water_content_33_j_kg: float | NDArray, water_content_1500_j_kg: float | NDArray
) -> float:
    """Return b soil parameter.

    Args:
    ----
        water_content_33_j_kg: water content at -33 J/kg
        water_content_1500_j_kg: water content at -1500 J/kg

    References:
    ----------
        Saxton, K.E., Rawls, W.J., 2006. Soil water characteristic estimates by texture
         and organic matter for hydrologic solutions. Soil Sci. Soc. Am. J. 70,
         1569-1578.

    Examples:
    --------
        >>> get_b_value(0.08, 0.03)
        3.89

    """
    result = (math.log(1500) - math.log(33)) / (
        math.log(water_content_33_j_kg) - math.log(water_content_1500_j_kg)
    )
    return round(result, 2)

get_bulk_density(clay, sand, organic_matter)

Return bulk density (Mg/m3 or g/cm3).

clay: clay content (fraction)
sand: sand content (fraction)
organic_matter: organic matter (%)

References:

Saxton, K.E., Rawls, W.J., 2006. Soil water characteristic
estimates by texture and organic matter for hydrologic solutions. Eq. 5,6
Soil Sci. Soc. Am. J. 70, 1569-1578.

Examples:

>>> get_bulk_density(clay=0.03, sand=0.92, organic_matter=1.906)
1.43
>>> get_bulk_density(clay=0.15, sand=0.2, organic_matter=2.29)
1.39
Source code in environmental_biophysics/soil.py 
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
def get_bulk_density(
    clay: float | NDArray, sand: float | NDArray, organic_matter: float | NDArray
) -> float:
    """Return bulk density (Mg/m3 or g/cm3).

    Args:
    ----
        clay: clay content (fraction)
        sand: sand content (fraction)
        organic_matter: organic matter (%)

    References:
    ----------
        Saxton, K.E., Rawls, W.J., 2006. Soil water characteristic
        estimates by texture and organic matter for hydrologic solutions. Eq. 5,6
        Soil Sci. Soc. Am. J. 70, 1569-1578.

    Examples:
    --------
        >>> get_bulk_density(clay=0.03, sand=0.92, organic_matter=1.906)
        1.43
        >>> get_bulk_density(clay=0.15, sand=0.2, organic_matter=2.29)
        1.39

    """
    x1 = (
        0.078
        + 0.278 * sand
        + 0.034 * clay
        + 0.022 * organic_matter
        - 0.018 * sand * organic_matter
        - 0.027 * clay * organic_matter
        - 0.584 * sand * clay
    )
    x2 = -0.107 + 1.636 * x1
    field_capacity = get_vol_water_content_33_j_kg(clay, sand, organic_matter)  # m3/m3
    sat_water_content = 0.043 + field_capacity + x2 - 0.097 * sand
    result = (1 - sat_water_content) * MIN_SOIL_PARTICLE_DENS
    return round(result, 2)

get_evap_lim_water_content(field_capacity_water_content, air_dry_water_content, water_content)

Return evaporation limitation based on water content [m3/m3].

field_capacity_water_content: field_capacity water content [m3/m3]
air_dry_water_content: air dry water content [m3/m3]
water_content: water content [m3/m3]

References:

Kemanian, A. R., and C. O. Stockle. 2010. C-Farm: A simple model to evaluate
 the carbon balance of soil profiles. Eur. J. Agron. 32(1):22-29

Examples:

>>> get_evap_lim_water_content(0.35, 0.05, 0.25)
0.296

>>> get_evap_lim_water_content(0.25, 0.05, 0.15)
0.125
Source code in environmental_biophysics/soil.py 
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
def get_evap_lim_water_content(
    field_capacity_water_content: float | NDArray,
    air_dry_water_content: float | NDArray,
    water_content: float | NDArray,
) -> float:
    """Return evaporation limitation based on water content [m3/m3].

    Args:
    ----
        field_capacity_water_content: field_capacity water content [m3/m3]
        air_dry_water_content: air dry water content [m3/m3]
        water_content: water content [m3/m3]

    References:
    ----------
        Kemanian, A. R., and C. O. Stockle. 2010. C-Farm: A simple model to evaluate
         the carbon balance of soil profiles. Eur. J. Agron. 32(1):22-29

    Examples:
    --------
        >>> get_evap_lim_water_content(0.35, 0.05, 0.25)
        0.296

        >>> get_evap_lim_water_content(0.25, 0.05, 0.15)
        0.125

    """
    assert (
        field_capacity_water_content and air_dry_water_content and water_content
    ) >= 0
    assert (
        field_capacity_water_content and air_dry_water_content and water_content
    ) <= 1
    assert field_capacity_water_content > air_dry_water_content
    assert field_capacity_water_content >= water_content
    result = (
        (water_content - air_dry_water_content)
        / (field_capacity_water_content - air_dry_water_content)
    ) ** 3
    return round(result, 3)

get_organic_matter(clay)

Calculate organic matter based on clay content.

clay: clay content (0-1)

References:

Hassink, J., and A. P. Whitmore. 1997. A Model of the Physical Protection of
 Organic Matter in Soils. Soil Sci. Soc. Am. J. 61(1):131-139.

Examples:

>>> get_organic_matter(0.5)
3.41

>>> get_organic_matter(0.03)
1.91
Source code in environmental_biophysics/soil.py 
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
def get_organic_matter(clay: float | NDArray) -> float:
    """Calculate organic matter based on clay content.

    Args:
    ----
        clay: clay content (0-1)

    References:
    ----------
        Hassink, J., and A. P. Whitmore. 1997. A Model of the Physical Protection of
         Organic Matter in Soils. Soil Sci. Soc. Am. J. 61(1):131-139.

    Examples:
    --------
        >>> get_organic_matter(0.5)
        3.41

        >>> get_organic_matter(0.03)
        1.91

    """
    result = 1.81 + 0.032 * clay * 100
    return round(result, 2)

get_sat_water_content(bulk_density)

Return the saturated water content (m3/m3).

bulk_density: bulk density (Mg / m3)

References:

Campbell, G.S., 1985. Soil physics with BASIC: Transport models for soil-plant
 systems. Elsevier, Amsterdam.

Examples:

>>> get_sat_water_content(bulk_density=1.3)
0.509
Source code in environmental_biophysics/soil.py 
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
def get_sat_water_content(bulk_density: float | NDArray) -> float:
    """Return the saturated water content (m3/m3).

    Args:
    ----
        bulk_density: bulk density (Mg / m3)

    References:
    ----------
        Campbell, G.S., 1985. Soil physics with BASIC: Transport models for soil-plant
         systems. Elsevier, Amsterdam.

    Examples:
    --------
        >>> get_sat_water_content(bulk_density=1.3)
        0.509

    """
    result = 1 - bulk_density / MIN_SOIL_PARTICLE_DENS
    return round(result, 3)

get_vol_water_content_1500_jkg(clay, sand, organic_matter)

Return the volumetric water content at permanent wilting point (1500 J/kg).

clay: clay content (fraction)
sand: sand content (fraction)
organic_matter: organic matter (%)

References:

Saxton, K.E., Rawls, W.J., 2006. Soil water characteristic estimates by texture
 and organic matter for hydrologic solutions. Soil Sci. Soc. Am. J. 70,
 1569-1578. eq.1 R2=0.86

Wilting point volumetric water content (m3/m3).

Examples:

>>> get_vol_water_content_1500_jkg (0.03,0.92,1.906)
0.03

>>> get_vol_water_content_1500_jkg (0.33,0.09,2.866)
0.21
Source code in environmental_biophysics/soil.py 
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
def get_vol_water_content_1500_jkg(
    clay: float | NDArray, sand: float | NDArray, organic_matter: float | NDArray
) -> float:
    """Return the volumetric water content at permanent wilting point (1500 J/kg).

    Args:
    ----
        clay: clay content (fraction)
        sand: sand content (fraction)
        organic_matter: organic matter (%)

    References:
    ----------
        Saxton, K.E., Rawls, W.J., 2006. Soil water characteristic estimates by texture
         and organic matter for hydrologic solutions. Soil Sci. Soc. Am. J. 70,
         1569-1578. eq.1 R2=0.86

    Returns:
    -------
        Wilting point volumetric water content (m3/m3).

    Examples:
    --------
        >>> get_vol_water_content_1500_jkg (0.03,0.92,1.906)
        0.03

        >>> get_vol_water_content_1500_jkg (0.33,0.09,2.866)
        0.21

    """
    x1 = (
        0.031
        - 0.024 * sand
        + 0.487 * clay
        + 0.006 * organic_matter
        + 0.005 * sand * organic_matter
        - 0.013 * clay * organic_matter
        + 0.068 * sand * clay
    )
    result = -0.02 + 1.14 * x1
    return round(result, 2)

get_vol_water_content_33_j_kg(clay, sand, organic_matter)

Return the volumetric water content at field capacity (33 J/kg) (m3/m3).

clay: clay content (fraction)
sand: sand content (fraction)
organic_matter: organic matter (%)

References:

Saxton, K.E., Rawls, W.J., 2006. Soil water characteristic estimates by texture
 and organic matter for hydrologic solutions. Soil Sci. Soc. Am. J. 70,
 1569-1578. eq.2 R2=0.63.

Examples:

>>> get_vol_water_content_33_j_kg (clay=0.03, sand=0.92, organic_matter=1.906)
0.0764
>>> get_vol_water_content_33_j_kg (clay=0.33, sand=0.09, organic_matter=2.866)
0.3829
Source code in environmental_biophysics/soil.py 
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
def get_vol_water_content_33_j_kg(
    clay: float | NDArray, sand: float | NDArray, organic_matter: float | NDArray
) -> float:
    """Return the volumetric water content at field capacity (33 J/kg) (m3/m3).

    Args:
    ----
        clay: clay content (fraction)
        sand: sand content (fraction)
        organic_matter: organic matter (%)

    References:
    ----------
        Saxton, K.E., Rawls, W.J., 2006. Soil water characteristic estimates by texture
         and organic matter for hydrologic solutions. Soil Sci. Soc. Am. J. 70,
         1569-1578. eq.2 R2=0.63.

    Examples:
    --------
        >>> get_vol_water_content_33_j_kg (clay=0.03, sand=0.92, organic_matter=1.906)
        0.0764
        >>> get_vol_water_content_33_j_kg (clay=0.33, sand=0.09, organic_matter=2.866)
        0.3829

    """
    x1 = (
        0.299
        - 0.251 * sand
        + 0.195 * clay
        + 0.011 * organic_matter
        + 0.006 * sand * organic_matter
        - 0.027 * clay * organic_matter
        + 0.452 * sand * clay
    )
    result = -0.015 + 0.636 * x1 + 1.283 * x1**2
    return round(result, 4)

get_water_content(sat_water_content, air_entry_potential, campbell_b, water_potential)

Return Soil water content (m3/m3).

sat_water_content: saturation water content (m3/m3)
air_entry_potential: air entry water potential (J/kg)
campbell_b: soil moisture release curve parameter
water_potential: matric water potential (J/kg)

References:

Campbell, G.S., 1985. Soil physics with BASIC: Transport models for soil-plant
 systems. Elsevier, Amsterdam. pp.80

Examples:

>>> get_water_content(0.5,-1.5,5,-52.7)
0.2454
Source code in environmental_biophysics/soil.py 
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
def get_water_content(
    sat_water_content: float | NDArray,
    air_entry_potential: float | NDArray,
    campbell_b: float | NDArray,
    water_potential: float | NDArray,
) -> float:
    """Return Soil water content (m3/m3).

    Args:
    ----
        sat_water_content: saturation water content (m3/m3)
        air_entry_potential: air entry water potential (J/kg)
        campbell_b: soil moisture release curve parameter
        water_potential: matric water potential (J/kg)

    References:
    ----------
        Campbell, G.S., 1985. Soil physics with BASIC: Transport models for soil-plant
         systems. Elsevier, Amsterdam. pp.80

    Examples:
    --------
        >>> get_water_content(0.5,-1.5,5,-52.7)
        0.2454

    """
    result = sat_water_content * (water_potential / air_entry_potential) ** (
        -1 / campbell_b
    )
    return round(result, 4)

get_water_potential(sat_water_content, air_entry_potential, campbell_b, water_content)

Return Soil Water Potential (J/kg).

sat_water_content: saturation water content (m3/m3)
air_entry_potential: air entry water potential (J/kg)
campbell_b: soil moisture release curve parameter
water_content: water content (m3/m3)

References:

Campbell, G.S., 1985. Soil physics with BASIC: Transport models for soil-plant
 systems. Elsevier, Amsterdam. Eq. 5.9

Examples:

>>> get_water_potential (0.5, -1.5, 5, 0.25)
-48.0

>>> get_water_potential (0.20, -1.0, 4, 0.25)
-0.4096
Source code in environmental_biophysics/soil.py 
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
def get_water_potential(
    sat_water_content: float | NDArray,
    air_entry_potential: float | NDArray,
    campbell_b: float | NDArray,
    water_content: float | NDArray,
) -> float:
    """Return Soil Water Potential (J/kg).

    Args:
    ----
        sat_water_content: saturation water content (m3/m3)
        air_entry_potential: air entry water potential (J/kg)
        campbell_b: soil moisture release curve parameter
        water_content: water content (m3/m3)

    References:
    ----------
        Campbell, G.S., 1985. Soil physics with BASIC: Transport models for soil-plant
         systems. Elsevier, Amsterdam. Eq. 5.9

    Examples:
    --------
        >>> get_water_potential (0.5, -1.5, 5, 0.25)
        -48.0

        >>> get_water_potential (0.20, -1.0, 4, 0.25)
        -0.4096

    """
    assert sat_water_content > 0, "sat water content must be positive"
    assert water_content > 0, "water content must be positive"

    return round(
        air_entry_potential * (sat_water_content / water_content) ** campbell_b,
        4,
    )