Which heats up faster air or soil?

The specific heat of a substance is the amount of heat energy it takes to raise the temperature of the substance 1o C. A substance with a high specific heat requires more heat to increase in temperature than a substance with a low specific heat.

Air has a specific heat of about 1.005 Kj/Kg/degree C.

Most soils are mostly composed of mineral particles, air and water. The specific heat of dry soil is about 0.80 Kj/kg/degree C. However, since the specific heat of water is very high (4.2 Kj/kg/degree C), soils often have a higher specific heat than air, and heat up more slowly than the air.

So it ultimately depends on the amount of moisture in the soil. A bone-dry soil can heat up quicker than air, but a wet soil will take longer to heat up than the air.