Yajing Wang1, Yili Lu1, Tusheng Ren1 and Robert Horton2, (1)Department of Soil & Water, China Agricultural University, Beijing, China (2)Iowa State University, Ames, IA
Soil volumetric water content (q) measured with the heat pulse method is influenced by the specific heat capacity of soil solids (cs), yet there are inconsistent reports about cs values. In this study, we determined soil cs with differential scanning calorimetry on nine soils, and partitioned cs into specific heats of soil minerals (cm), organic matter (co), and tightly bound water (ctbw). Soil cm was measured for organic matter-removed samples dried at 200oC, and cs values were measured for original samples dried at 105oC. For the nine soils, cm averaged 0.736 MJ Mg-1 K-1 (from 0.717 to 0.759 MJ Mg-1 K-1), and cs averaged 0.750 MJ Mg-1 K-1 (from 0.718 to 0.772 MJ Mg-1 K-1). Tightly bound water showed negligible influence on cs values. Soil cm was influenced mainly by soil specific surface area and varied linearly with temperature from 10 to 55oC. The heat pulse measurements were conducted on Soils 6, 8 and 9. When the widely accepted cs value of 0.725 MJ Mg-1 K-1 was used, the heat pulse method overestimated q by 0.054 m3 m-3 on average. The error was reduced significantly (0.042 m3 m-3) when cs values of 0.761 MJ Mg-1 K-1 (Soil 6), 0.745 MJ Mg-1 K-1 (Soil 8) and 0.781 MJ Mg-1 K-1 (Soil 9) were used.