Ecosystem water use efficiency in an irrigated cropland in the North China Plain

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Journal Article
Journal of Hydrology, 2009, 374 (3-4), pp. 329 - 337
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The eddy covariance technique and the cuvette method were used to investigate water use efficiency in an irrigated winter wheat (Triticum asetivum L.)/summer maize (Zea mays L.) rotation system in the North China Plain. The results show that ecosystem water use efficiency (WUEe) changed diurnally and seasonally. Daily maximal WUEeappeared in the morning. WUEegenerally peaked in late April in wheat field and in late July/early August in maize field. From 2003 to 2006, seasonal mean WUEewas 6.7-7.4 mg CO2g-1H2O for wheat and 8.4-12.1 mg CO2g-1H2O for maize. WUEewas much lower than canopy water use efficiency (WUEc) under small leaf area index (LAI) but very close to WUEcunder large LAI. With the increase in LAI, WUEeenlarged rapidly under low LAI but slowly when LAI was higher than one. WUEewas greater on the cloudy days than on the sunny days. Under the same solar radiation, WUEewas higher in the morning than in the afternoon. The ratio of internal to ambient CO2partial pressure (Ci/Ca) decreased significantly with the increase in photosynthetically active radiation (PAR) when PAR was lower than the critical values (around 500 and 1000 μmol m-2s-1for wheat and maize, respectively). Beyond critical PAR, Ci/Cawas approximately constant at 0.69 for wheat and 0.42 for maize. Therefore, when LAI and solar radiation was large enough, WUEehas negative correlation with vapor pressure deficit in both of irrigated wheat and maize fields. © 2009 Elsevier B.V.
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