Collect and record data. Generate a graph based on data. Analyze data and make conclusions concerning how soil moisture affects soil temperature. For example, the maximum daily temperature at deep soil depths is delayed, even by several hours, after the time when the air temperature reaches a maximum. Conversely, on cool nights, the deep soil layers don't cool as fast as surface layers because of the insulating effect of the overlying soil.
Heat flow is slower in soil than in the atmosphere.
The deeper the soil layer, the longer it takes a temperature change to reach it, thus, the less will be the actual temperature fluctuation from day to day or week to week. 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.