The amount of energy entering the soil is contingent largely upon the color, the slope, and the vegetative cover of the soil under consideration. Dark soils will absorb more energy from the sun than light colored soils and red or yellow soils will show a more rapid temperature rise tan those that are white. Studies have shown that the nearer the angle of incidence of the sun's rays approaches the perpendicular, the greater will be the absorption. This means that a southeasterly inclination is warmest in the early season, a southerly slope during midseason, and a southwesterly slope in the fall. This is not true in all locations universally, but it does indicate that slopes vary in their desirability depending on the crop that you choose to grow.
Most gardeners prefer south or southeasterly slopes.
Another important factor in the temperature of the soil is determined if the soil is bare or covered with vegetation as this affects the amount of insolation that is received. A field of grass doesn't have much effect on temperature fluctuations but a forest does. Bare soils will warm more quickly and cool off more rapidly that those covered with vegetation or even with mulches. During the winter, frost penetration is considerably greater in noninsulated land. Mineral soils will not only vary in respect to the energy necessary to raise their temperature but also that this variation is largely in proportion to the amounts of water present.