Energy fluxes and the Priestley-Taylor parameter over winter wheat and maize in the North China Plain

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Journal Article
Hydrological Processes, 2004, 18 (12), pp. 2235 - 2246
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Surface energy fluxes above the canopies of well-irrigated winter wheat and maize in the North China Plain were measured by the Bowen-ratio energy balance technique in 1999-2000. Seasonal variation of the ratio of latent heat flux λE to available energy Rn - G showed that the ratio of λE to Rn - G exceeded 83% when leaf area index (LAI) varied from 2.0 to 6.0. The seasonal trend of evaporative fraction (EF) for winter wheat was similar to that of LAI before senescence stage, which is a critical factor controlling EF, which itself reflects the partitioning of available energy into λE. The Priestley-Taylor parameter α over the wheat and maize canopies changed greatly over the course of a growing season, and the seasonal average α of winter wheat was 1.17 and 1.26, and that of maize was 1.06 and 1.09 in the two consecutive years. α for winter wheat was exponentially correlated to 0-20 cm surface soil moisture, but not for maize and with the increase of soil depths, the correlation between α and soil moisture was weak. Under different soil moisture conditions, a linear correlation between extractable soil water and leaf water potential ψ for winter wheat was found. Copyright 2004 John Wiley and Sons, Ltd.
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