[877] - Improving the stem heat balance method for determining sap-flow in wheat

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Langensiepen, M., Kupisch, M., Graf, A., Schmidt, M., Ewert, F., 2014. Improving the stem heat balance method for determining sap-flow in wheat. Agricultural and Forest Meteorology, 186, 34 - 42. DOI: 10.1016/j.agrformet.2013.11.007.
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Title(s):Main Title: Improving the stem heat balance method for determining sap-flow in wheat
Description(s):Abstract: A novel micro-sensor for measuring sap-flow in thin plant stems designed by Dynamax Inc. based on the heat-balance theory was applied in wheat (Triticum aestivum) grown under ambient field conditions. The sensor measures axial and radial temperature changes in a constantly heated and thermally insulated stem section. The temperatures are altered by sap-flow activity and this information is used to solve the stem energy balance equation with respect to its convective heat flow residual which indicates sap-flow. Results from four different field experiments show that the majority of heat energy input was diverted to radial heat flow, leaving only little energy partitioned to convective heat flow. Determinations of gravimetric sap-flow were extremely noisy in consequence, rendering the method unreliable for practical application. Temperature differences across the heater consistently correlated with fluctuating net-radiation however, which motivated us to establish an empirical method for determining gravimetric sap-flow based on this temperature information alone. Numerical simulations showed that gravimetric sap-flow and temperature difference are nearly linearly and positive correlated within an observed sap flow range between 0 and 1.7 g h−1, beyond which the relation became non-linear and even inverse at higher velocities. It remains to be tested whether such higher fluxes can be reached in practice and we provide a solution for these cases. Statistical noise overrode the error introduced by assuming a linear relation between sap flow and temperature difference within the range between 0 and 1.7 g h−1. The resulting factors were determined under stable sap flow conditions greater than 1 g h−1and used for generating daily cycles of sap flow using temperature information alone. The approach was successfully validated in 2011 and 2012 against independent measurements of latent heat flux conducted in closed and dense wheat fields using the eddy-covariance technique. We thereby improved the application of the new micro-sensor in wheat. Suggestions for further enhancements of the method are discussed.
Identifier(s):DOI: 10.1016/j.agrformet.2013.11.007
Responsible Party
Creator(s):Author: Matthias Langensiepen
Author: Moritz Kupisch
Author: Alexander Graf
Author: Marius Schmidt
Author: Frank Ewert
TR32 Topic:Vegetation
Subject(s):CRC/TR32 Keywords: Sap Flow, Numeric Modelling, Eddy Covariance
Topic Category:GeoScientificInformation
File Details
File Name:2013_Langensiepen_agrformet.pdf
Data Type:Text
Size(s):8 Pages
File Size:1332 kB (1.301 MB)
Date(s):Date Accepted: 2013-11-21
Date Submitted: 2014-04-10
Mime Type:application/pdf
Data Format:PDF
Download Permission:OnlyTR32
General Access and Use Conditions:According to the TR32DB data policy agreement.
Access Limitations:According to the TR32DB data policy agreement.
Licence:TR32DB Data policy agreement
Measurement Region:Ellebach
Measurement Location:Selhausen
Specific Informations - Publication
Article Type:Journal
Source:Agricultural and Forest Meteorology
Number Of Pages:8
Page Range:34 - 42
Metadata Details
Metadata Creator:Moritz Kupisch
Metadata Created:2014-06-18
Metadata Last Updated:2014-06-18
Funding Phase:2
Metadata Language:English
Metadata Version:V40
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