[Variation of apple tree canopy-air temperature difference and its relations to environment factors]

By using portable infrared thermometer, the canopy temperature (Tc) of apple tree in its main growth season was measured in 2002-2005. Combined with the synchronous micro-meteorological data on the canopy, such as net radiation (Rn), wind speed (V), air temperature (Ta) and relative humidity (RH), as well as the soil water content (SW) at 0-80 cm depth, the variation of apple tree canopy-air temperature differential (DeltaT) and its relationships to environmental factor were analyzed. The results showed that from bud stage to fruit-developing stage, there were several peaks in the diurnal curve of DeltaT, with the maximum at 12:00-13:00 in fine days, and the absolute value of DeltaT in fine days was higher than that in overcast days. Based on data of 2003 and 2004, the DeltaT at 14:00 was significantly correlated with the RH, V, Rn, SW in fine days, and the regression equation was DeltaT = 7.159 - 0.002Rn - 0.061V - 0.7RH - 46.0SW (P < 0.01, r = 0.825). The partial coefficient for Rn, RH, V and SW was 0.125, -0.078, -0.036, -0.874, respectively, and the stepwise regression equation was DeltaT = 5.317 - 43.1SW (P < 0.01), suggesting that SW was the most important environmental factor affecting DeltaT. After validated with the measured data in 2002 and 2005, it was found that the measured DeltaT was highly accorded with the simulated one (r = 0.9083, P < 0.01, n = 40), and thus, it was of possibility to use the data of DeltaT at 14:00 in fine days to predict the soil water content in apple orchard.