Water, heat fluxes and water use efficiency measurement and modeling above a farmland in the North China Plain
Net radiation (Rn), water vapor flux (LE), sensible heat flux (Hs) and soil heat flux (G)were measured above a summer maize field with the eddy-covariance technique, simulation and analysis of water, heat fluxes and crop water use efficiency were made with the RZ-SHAW model at the same time in this study. The results revealed significant diurnal and seasonal variability of water vapor flux for summer maize. Most part of Rn was consumed by the evapotranspiration of the summer maize. The proportion of water vapor flux to net radiation ((LE/Rn) increased with the crop development and peaked around milk-filling stage with a value of 60%, a slightly lower than that obtained by the RZ-SHAW model. Daily evapotranspiration estimated by the model agreed with the results measured with the eddy-covariance technique, indices of agreement (IA) for hourly water vapor fluxes simulated and measured were above 0.75, root mean square errors (RMSE) were no more than 1.0. Diurnal patterns of Hs showed the shape of inverted "U" shifted to the forenoon with a maximum value around 11:30 (Beijing time), while LE exhibited an inverted "V" with a maximum value at around 13:00, about an hour later than Hs. Diurnal change of CO2showed an asymmetrical "V" curve and its maximal rates occurred at about 11:30. Variations of water use efficiency during the phonological stages of the summer maize showed a rapid increase with the photosynthetic photon flux density (PPFD) after sunrise, a state of equilibrium around 10:00 followed a decrease. Maximum values of water use efficiency were 24.3, and its average value ranged from 7.6 to 10.3 g kg-1.
作 者： Qin Zhong YU Qiang XU Shouhua Hu Bingmin SUN Xiaomin Liu Enmin WANG Jishun YU Guirui ZHU Zhilin 作者单位： Qin Zhong(Ecology academy, College of Life Science, Zhejiang University, Hangzhou 310029,China)YU Qiang,XU Shouhua,SUN Xiaomin,Liu Enmin,WANG Jishun,YU Guirui,ZHU Zhilin(Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China)
Hu Bingmin(Ecology academy, College of Life Science, Zhejiang University, Hangzhou 310029,China;College of Science, Zhejiang University, Hangzhou 310029, China)
刊 名： 中国科学D辑（英文版） SCI 英文刊名： SCIENCE IN CHINA (EARTH SCIENCES) 年，卷(期)： 2005 48(z1) 分类号： P4 关键词： water vapor flux CO2 flux water use efficiency RZ-SHAW model maize North China Plain