Soil Temperature Regimes in the Lienhuachih Area of Central Taiwan

Soil temperature and its fluctuations, which affect the soil’s physical and chemical properties, biological activity, and vegetation growth, are considered to be important characteristics of soil. Historical soil temperature records of 3 observations at 09:00, 14:00, and 21:00 within a day from 1982 to 1991 in the Lienhuachih area were reorganized and analyzed to understand seasonal and daily temperature fluctuations in the study area. The results indicated that the yearly average temperatures for the air, and soil layers at 0, 5, 10, 20, and 30 cm from the soil surface were 21.4, 22.0, 22.7, 22.7, 23.1, and 22.8℃, respectively, and the maximum and minimum monthly average soil temperatures respectively occurred in July and January for air and all soil layers. The highest values of the monthly average soil temperature mostly occurred at 20-cm depth from the soil surface, which indicated that soil at this depth contained the maximum heat as a result of on energy balance from receiving and emitting solar radiation and the internal energy of the earth. Ranges of yearly temperature fluctuations were 14.3, 13.2, 13.0, 11.6, 11.1, and 10.5℃ for air and soil depths at 0, 5, 10, 20, and 30 cm below the soil surface, respectively. This indicates that the deeper the soil the smaller changes in temperature that were observed. The highest soil temperatures within a day were always the records observed at 14:00 for all depths, while the lowest were records observed at 09:00. The magnitude of daily soil temperature fluctuations exceeding 3℃ only occurred in soil layers at < 5 cm in depth. In addition, fluctuations within a day were insignificant in layers deeper than 5 cm from the soil surface in the Lienhuachih area.