The heat supply to the soil surface from external sources is reduced by opaque soil coverings, such as mulches, which act as insulators. A sun angle less than perpendicular to the soil surface also supplies less heat per unit of soil area. Heat that is absorbed by soil can be lost by use in evaporating soil water. In a dark soil where the color is caused by large amounts of humus, the larger amounts of water held by the humus may offset the increased heat adsorption due to the dark color. Although compacted soils have better heat conductivity than loosened soil, they also have more material to heat per volume of soil.
Students generate a hypothesis that relates to the lab.
Students predict which soil type will have the greatest temperature change over a given period of time. Gather light sources, thermometers, rulers, water, graduated cylinders and timing devices. Have copies of data table ready if instructor chooses to use it. Students should add different amount of water to each square. The important thing here is that the same textured soil samples will have different water contents.