Simultaneous measurements of water vapor, sensible heat, carbon dioxide and momentum fluxes were made above and within plant canopies of a wheat field at Zhangye oasis in June, 1992, using the eddy correlation method. The diurnal variations of energy and carbon dioxide budget components and related meteorological parameters were obtained. Vertical fluxes of water vapor, sensible heat and carbon dioxide above plant canopies were predominant, compared with the fluxes at the middle layer of the plant canopy. This implies that, in the daytime, the upper part of dense plant canopies (LAI = 5) was an active source region of water vapor as well as an active sink region of carbon dioxide. A moderate and steady wind from the surrounding warmer desert and Gobi areas increased an upward water vapor flux and caused a significant downward sensible heat flux above plant canopies; these phenomena are the so-called oasis effects peculiar to the arid region.
The diurnal variations of turbulent fluxes and related quantities observed in a wheat field were compared with the results of Goudriaan's simulation model. The model simulates well some primary characteristics of wheat crop micrometeorology; large loss of latent heat in upper parts of plant canopies, and a significant downward sensible heat flux under moderate wind speed conditions.