Abstract: Abstract: Soil thermal conductivity (?) is a key parameter for studying surface energy balance and coupled heat and water transfer in soil. ? can be obtained by heat pulse method or semi-empirical or empirical models, with both models based on the information of soil texture, water content (?) and bulk density (?b).The pedotransfer model has the advantages of simple form and having no requirement of soil minerology information. This pedotransfer ? model, however, has not been applied comprehensively under field conditions where ? displays strong spatial and temporal variability. The objectives of this study are to determine the spatial and temporal changes of ? as related to ? and ?b in tilled soil layers, and to test the feasibilities of the pedotransfer ? model for estimating field ? with the information of soil texture, ? and ?b. Two independent field experiments were conducted: one study of different tillage treatment's effect on ? variations and another post-tillage soil structure dynamic study on ? at 2 soil depths due to alternate wetting and drying. For the tillage method study, ? measurements were carried out in the field, and soil cores were taken to determine ? and ?b gravimetrically. For the soil structure dynamic study, in situ ? changes were monitored with time domain reflectometry (TDR) technique, the dynamic ?b values were determined gravimetrically after each rainfall event, and the corresponding ??data were obtained from the collected intact soil cores by heat-pulse sensors. The results showed that ? and ?b were the key factors that affected ? in tilled soil layers. In 0-10 cm soil layer, the ?, ? and ?b values in no tillage treatment plot were significantly higher than those of the moldboard and rotary tillage plots. Soil ? values of the 10-20 cm soil layer were higher than that in the 0-10 cm layer, and the trends were consistent with that of ? and ?b regarding tillage treatment and soil depth. For the post-tillage soil structure dynamic study, ?b was increased gradually with time and soil depth and became relatively stable after 4 wetting/drying (W/D) cycles, i.e., from 0.98 to 1.16 g/cm3 for the 0-5 cm layer, and from 1.09 to 1.28 g/cm3 for the 5-10 cm layer. The magnitude of the change was relatively small among the first 3 W/D cycles when the degrees of saturation were relatively low, and ?b in the 5-10 cm layer reached the maximum after the fourth W/D cycle when the soil was nearly saturated, with the change became less significant thereafter. Comparison between measured and modeled values showed that the pedotransfer ? model provided reliable ??with RMSE of 0.09 W/(m·K) and mean bias of -0.01 W/(m·K). Our analysis also highlighted the fact that when ?b varied over time due to soil structure change, using a constant ?b (measured either right after tillage or at the end of the experiment) would introduce larger errors for ? estimations. The pedotransfer ? model for estimating soil ? could be useful for simulating heat transfer in tilled soil layers.