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United States Department of Agriculture

Agricultural Research Service

Title: Canopy Surface and Stomatal Resistances of Alfalfa in a Semi-Arid, Advective Environment

item Todd, Richard
item Evett, Steven
item Howell, Terry
item Tolk, Judy

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: June 12, 1998
Publication Date: N/A

Technical Abstract: Canopy stomatal resistance represents the canopy-scale response of stomata to the environment. Canopy surface resistance of the 'big leaf' model is influenced not only by the bulk response of stomata, but also by factors such as energy exchange at the soil surface. Canopy resistances of irrigated alfalfa were estimated by inversion of single- or two-layer combination equation models using field data collected at a weighing lysimeter installation. Canopy stomatal resistance of full cover alfalfa averaged 62 s m**-1 in 1996 and 49 s m**-1 in 1997. Canopy surface resistance, calculated with aerodynamic resistance that assumed unequal roughness lengths for heat and momentum, averaged 32 s m**-1 in 1996 and 22 s m**-1 in 1997. Canopy stomatal resistance decreased with increasing leaf area index (LAI) in 1997 until LAI>3, when it approached a constant. However, in 1996 canopy stomatal resistance increased as LAI increased above four. Greater canopy stomatal resistances were correlated with higher vapor pressure deficits in 1996.

Last Modified: 4/22/2015
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