The purpose of this experiment was to ascertain whether texture has a significant role in determining the thermal conductivity of soil. An attempt was made to collect samples which would be good representatives of each of the three soil textural classes. To eliminate moisture as a variable, all samples were oven-dried, and to eliminate color as a variable, all samples were heated from below.
A test chamber was constructed to keep the heating of the soil samples uniform by keeping the samples a constant distance from the heat lamp. Additionally, the test chamber’s sides were enclosed with aluminum sheets to minimize the influence of the air in the room on soil samples being tested.
Each sample was first placed in a freezer to lower its temperature and allow a greater increase in temperature to occur during heating. Exact starting and ending temperatures were not a concern, since it was the slope of the increase that was the focus of the investigation. The warming of each sample over the heat source was measured for twenty minutes, enough time to establish a distinct trend. Soil from each collection site was divided into two testing samples, which were each tested five times.
The data collected showed a direct relationship between thermal conductivity and texture as well as an indirect relationship through the variables influenced by texture, such as pore space and particle density. The direct relationship of texture to thermal conductivity shown was that as particle size decreased, thermal conductivity increased. The indirect relationship shown was that as particle density increases, thermal conductivity increases, and as pore space increases, thermal conductivity decreases. Another conclusion that can be drawn from the data is that in nature, it may ultimately be the water capacity of a soil (which is itself influenced by texture) which determines its thermal conductivity.