Soil temperature is a measurement of the warmth of soil and is a factor for the germination, blooming, and for timing seeding of plants. The air temperature directly affects the temperature of the soil since the sun heats the air that comes in direct contact with the ground. The composition of the soil impacts the heat capacity (the ability of the soil to store heat), meaning different types of soils can heat and cool faster. This means the temperatures of these layers of soil can fluctuate quickly.
Another factor that contributes to soil temperature is the seasonal angle of the sun.