Specific Heat Capacity of Soil Solids: Influences of Clay Content, Organic Matter, and Tightly Bound Water

The specific heat capacity of soil solids (c(s)) is a key parameter affecting heat storage and transfer in soils. In soil and geophysical applications, c(s) is often assumed to be a constant with little variations across soils. In this study, we determined the specific heat capacities of nine soils by using differential scanning calorimetry (DSC), evaluated the effects of clay and organic matter (OM) contents on the c(s) of original and OM-free soil samples at room temperature, and quantified the changes of c(s) caused by the existence of tightly bound water (TBW). On average, the nine mineral soils had a c(s) of 0.750 MJ Mg-1 K-1, close to the commonly accepted c(s) value. However, for the original soils dried at 105 degrees C, clay content did not obviously influence the c(s) value and c(s) increased linearly with both OM and TBW contents, indicating that inaccurate c(s) data were likely if the changes in the OM fraction in soil solids and adsorbed TBW were ignored. In addition, relatively large values for the specific heat capacity of soil minerals (c(m)) were observed in fine-textured soils compared with coarse-textured soils. Two preliminary functions were developed for estimating c(m) and c(s) from the soil's clay and OM contents.