ARS | Publication request: Contrasting Methods for Measuring Evapotranspiration in Soybean

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 5, 2009
Publication Date: November 5, 2009
Citation: Singer, J.W., Heitman, J.L., Hernandez Ramirez, G., Sauer, T.J., Prueger, J.H., Hatfield, J.L. 2009. Contrasting Methods for Measuring Evapotranspiration in Soybean [CD-ROM]. In: ASA-CSSA-SSSA Annual Meeting Abstracts, Nov. 1-5, 2009, Pittsburgh, PA.

Technical Abstract: Crop scientists are often interested in canopy rather than leaf water fluxes. Canopy measurements are difficult to obtain because instrumentation is expensive, investigations require a high level of comprehension in micrometeorological methods, and treatment comparisons are usually limited. The objective of this research was to contrast measurement of evapotranspiration (ET) using eddy covariance methods compared to summing the evaporation (E) and transpiration (T) components of ET in a soybean canopy during reproductive development. Soil water evaporation was estimated using weighable microlysimeters by mass balance and T was estimated using leaf gas exchange on sunlit and shaded leaves. Summing E+T always produced higher estimates than eddy covariance. Differences ranged from 0.74 mm to 1.13 mm or from 25 to 50% higher when measurements occurred between 1000 and 1400 CDT. Soil water evaporation accounted for between 4 and 11% of the total ET. The smallest difference between methods (21%) was measured on a day with the highest turbulence intensity, indicating that conditions favoring transport of water vapor from the canopy to the boundary layer enhance agreement between the two methods.