Abstract: Based on soil surface temperature of six soil layers at depth of 5cm, 10cm, 20cm, 40cm, 60cm and 80cm from June 15 to July 14 in 2010, the variation of soil shallow layer temperature and soil thermal diffusivity was studied. The results showed that there were an 〖JP2〗obvious sinusoidal diurnal variations of soil temperature from top layers(<20cm),〖JP〗 buffer layer (20-40cm) for sinusoidal fluctuation and linear oscillation while undetectable diurnal changes below 40cm soil layers. The amplitude (A) and phase (φ) of diurnal soil temperature variations declined exponentially (A=4.60e-6.74z，R2〖KG-1mm〗=0.93) and linearly (φ=6.14z+7.67，R2〖KG-1mm〗=0.95) with the soil depth (z) increased, respectively. The response to pulse precipitation of soil temperature at top layers changed gradually, and resulted in the same thermal soil layers. Soil thermal diffusivity (κ) was enhanced exponentially (κ=2×10-7e4.21z，R2〖KG-1mm〗=0.92) with soil depth enhancement. There were totally opposite diurnal fluctuations between 34.7cm and 5.0cm. The depth of diurnal constant temperature strata was about 86.0-102.0cm.

Key words: Soil temperature amplitude, Sinusoidal analytical method, Amplitude method, Phase method