HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Baldocchi, D. D. Articles by Rosenberg, N. J. Search for Related Content PubMed Articles by Baldocchi, D. D. Articles by Rosenberg, N. J. Agricola Articles by Baldocchi, D. D. Articles by Rosenberg, N. J.

Mass and Energy Exchanges of a Soybean Canopy under Various Environmental Regimes¹

The environment of the east central Great Plains of North America can be very extreme during the course of a growing season. A field study was thus conducted during the summer of 1979 to examine the exchange of mass and energy between the atmosphere and a soybean canopy [Glycine max (L.) Merrill] for various environmental conditions experienced in the east central Great Plants of North America. The crop was planted in a Typic Argiudoll (Sharpsburg silty, clay loam) soil. Measurements of mass and energy exchange rates were made using the Bowen-ratio energy balance technique.

Hot, clear days dominated by sensible heat advection limited CO₂ exchange but increased latent heat flux. As a result, the CO₂-water flux ratio (CWFR), a measure of water-use efficiency, was low. Cloudy days suppressed both CO₂ and latent heat flux. This effect caused CWFR to be greater. Optimal conditions for photosynthesis and CWFR occurred in the absence of sensible heat advection on clear days with moderate temperatures.

Our measurements indicate that a developed soybean canopy (LAI of 4.1) did not become light saturated at photosynthetically active radiation (PAR) levels exceeding 400 Wm^–2. Optimal air temperatures for CO₂ exchange ranged between 29 and 32 C. Higher temperatures led to a reduction in CO₂, exchange. The CWFR was found to be dependent on both net radiation and sensible heat advection.

Key Words: Photosynthesis • Latent heat flux • Sensible heat flux • CO₂-water flux ratio • Water-use efficiency

² Research associate, associate professor, and professor, Center for Agric. Meteor. and Climat., Inst. of Agric. and Nat. Res., Univ. of Nebraska, Lincoln, NE 68583.

Received for publication October 22, 1980.