Acta Geographica Sinica ›› 2002, Vol. 57 ›› Issue (3): 335-344.doi: 10.11821/xb200203010

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Measurement and Analysis of Water, Heat and CO2 Flux from a Farmland in the North China Plain

ZHANG Yongqiang1,2, SHEN Yanjun2, LIU Changming1,2, Yu Qiang1, SUN Hongyong2, JIA Jinsheng1, TANG Changyuan3, AKIHIKO Kondoh3   

  1. 1. Institute of Geographic Sciences and Natural Resources Research, Beijing 100101, China;
    2. Institute of Agricultural Modernization Research, Shijiazhuang 050021, China;
    3. Chiba University, 33 Yayoi, Inage, Chiba 263-8522, Japan
  • Received:2001-12-16 Revised:2002-03-26 Online:2002-05-25 Published:2010-09-06
  • Supported by:

    National Natural Science Foundation of China, No. 40071008, 49871020, 49890330; Academician Agricultural Water-saving Foundation, Hebei Province of China, No. 01220703D; Special Fund for Major State Basic Research Project, No. CXIOG-C003-03

Abstract:

Surface energy fluxes including net radiation (Rn), latent heat flux (λE), sensible heat flux (H), soil heat flux (G) and carbon dioxide flux (FCO2) were measured by Bowen-ratio energy balance technique and eddy correlation technique from a farmland at Luancheng Agro-ecosystem Station, Chinese Academy of Sciences in the North China Plain from 1999 to 2001. Seasonal variation of a ratio of latent heat flux (λE) divided by net radiation flux (Rn) showed that Rn is mainly used to evapotranspirate by crops. λE/Rn was all higher than 70% during the four observed seasons in the two years. λE/Rn above maize canopy is slightly higher than that above winter wheat canopy. Seasonal average ratio of sensible heat flux (H) divided by Rn keeps about 15% above the field surface; seasonal average ratio of conductive heat flux (G) divided by Rn varies between 5% and 13%, and the average G/Rn from wheat canopy is evidently higher than that from maize canopy. Under given environmental conditions, when the available energy (Rn-G) is less than 200 W/m2, evaporative fraction (EF) decreases sharply; below Rn-G≈200 W/m2, EF decreases gradually until stabilizing at some specific value less than 1.0. The response process of EF to Rn-G under winter wheat field conditions is similar to that under the given conditions. With the increase of photosynthesis photo flux density (PPFD), carbon dioxide flux (FCO2) changes according to the curve of Michaelis-Mente. Water use efficiency (WUE) does not show the maximum when PPFD is the maximum at noon. On the contrary, WUE gradually decreased with PPFD equal to 1500 μmol m-2 s-1.

Key words: latent heat flux (λE), sensible heat flux (H), carbon dioxide flux, water use efficiency (WUE), the North China Plain