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| Titel |
A comparison of methods for determining field evapotranspiration: photosynthesis system, sap flow, and eddy covariance |
| VerfasserIn |
Z. Zhang, F. Tian, H. Hu, P. Yang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 3 ; Nr. 18, no. 3 (2014-03-18), S.1053-1072 |
| Datensatznummer |
250120307
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| Publikation (Nr.) |
 copernicus.org/hess-18-1053-2014.pdf |
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| Zusammenfassung |
| A multi-scale, multi-technique study was conducted to measure
evapotranspiration and its components in a cotton field under mulched drip
irrigation conditions in northwestern China. Three measurement techniques at
different scales were used: a photosynthesis system (leaf scale), sap flow
(plant scale), and eddy covariance (field scale). The experiment was
conducted from July to September 2012. To upscale the evapotranspiration from
the leaf to plant scale, an approach that incorporated the canopy structure
and the relationships between sunlit and shaded leaves was proposed. To
upscale the evapotranspiration from the plant to field scale, an approach
based on the transpiration per unit leaf area was adopted and modified to
incorporate the temporal variability in the relationship between leaf areas
and stem diameter. At the plant scale, the estimate of the transpiration
based on the photosynthesis system with upscaling was slightly higher
(18%) than that obtained by sap flow. At the field scale, the estimates of
transpiration derived from sap flow with upscaling and eddy covariance showed
reasonable consistency during the cotton's open-boll growth stage, during
which soil evaporation can be neglected. The results indicate that the
proposed upscaling approaches are reasonable and valid. Based on the
measurements and upscaling approaches, evapotranspiration components were
analyzed for a cotton field under mulched drip irrigation. During the two
analyzed sub-periods in July and August, evapotranspiration rates were 3.94
and 4.53 m day−1, respectively. The fraction of transpiration to
evapotranspiration reached 87.1% before drip irrigation and 82.3% after
irrigation. The high fraction of transpiration over evapotranspiration was
principally due to the mulched film above the drip pipe, low soil water content
in the inter-film zone, well-closed canopy, and high water requirement of the
crop. |
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