Heat capacity of a unit volume of soil

Soil volumetric heat capacity is the amount of energy required to raise the temperature of a unit volume of soil by one degree. Unlike thermal conductivity, volumetric heat capacity increases strictly linearly as soil water content increases. Volumetric heat capacity is also a linear function of bulk density.

To increase the temperature of wetter, denser soil requires more energy than to increase the temperature of drier, less dense soil, which has a lower volumetric heat capacity. This is one factor that can contribute to lower soil temperatures.

$\zeta_{soil} c_{p,soil}+\zeta_w c_{p,w} \nu_{soil}$