The function estimates soil thermal conductivity (W m^{-1} K^{-1}) using the methods of deVries (1963)
.

`soil_conductivity(x, lambda, g_a)`

- x
`numeric`

vector of volume fractions of soil constituents (e.g., clay, quartz, minerals other than quartz, organic matter, water, air). The volume fractions should sum to 1. Note that`x`

and`lambda`

values in the example correspond to these soil constituents.- lambda
`numeric`

vector of the thermal conductivities (W m^{-1}K^{-1}) of the soil constituents.- g_a
`numeric`

shape factor on soil particles. The soil particles are assumed to be ellipsoids with axes`g_a`

,`g_b`

, and`g_c`

, where`g_a + g_b + g_c = 1`

and`g_a = g_b`

. deVries (1952) suggests`g_a = g_b = 0.125`

.

`numeric`

soil thermal conductivity (W m^{-1} K^{-1}).

deVries DA (1952).
“Thermal Conductivity of Soil.”
*Nature*, **178**, 1074.
doi:10.1038/1781074a0
.

deVries DA (1963).
“Thermal Properties of Soils.”
In *Physics of Plant Environment*.
North Holland Publishing Company.
doi:10.1002/qj.49709038628
.

Other soil temperature functions:
`soil_specific_heat()`

,
`soil_temperature_equation()`

,
`soil_temperature_function()`

,
`soil_temperature_integrand()`

,
`soil_temperature()`