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MASS AND ENERGY EXCHANGES OF SOYBEANS: MICROCLIMATE-PLANT ARCHITECTURE INTERACTIONS
Abstract
A study was conducted during the growing seasons of 1979, 1980 and 1981 to evaluate the microclimate of a soybean (Glycine max L., Merrill) canopy and to determine the influence of alterations in plant architectural characteristics on its mass and energy exchanges. A Clark cv. canopy was studied in 1979. Two Harosoy cv. isolines differing in leaf pubescence density were studied in 1980 and two Clark cv. isolines differing in leaf width were studied in 1981. Fluxes of CO(,2), water vapor, sensible heat and momentum were measured by means of micrometeorological techniques. Crop water status was monitored by means of leaf water potential and stomatal resistance measurements. Soil moisture measurements were made gravimetrically and with a neutron probe. Considerable variability was observed in the wind speed regime within the canopy. Wind speeds were greater between rows than within the row. A reversal in the wind speed gradient was also found to occur in the lower portion of the canopy within the row. Increasing turbulent mixing distorted the canopy shape and increased wind speeds in the canopy. Canopy CO(,2) fluxes did not indicate a light-saturated photosynthetic mechanism. CO(,2) fluxes did, however, decrease dramatically as air temperatures exceeded 32 C and leaf water potentials dropped below -1.1 MPa. CO(,2)-water flux ratios (CWFR) decreased with increases in net radiation and stomatal resistance. A soybean isogene having increased leaf pubescence was found to have reduced water vapor exchange and increased sensible heat exchange. Leaf pubescence altered the partitioning of net radiation by facilitating the penetration of solar radiation into the canopy. Canopy CO(,2) exchange, crop water status and turbulent mixing were unaffected by leaf pubescence whereas CWFR was improved. A reduction in leaf width reduced water vapor exchange and increased sensible heat exchange. Net radiation, however, was not affected. The differential partitioning of net radiation was due to better penetration of solar radiation in the narrow-leaf canopy since it had a lower total leaf area. Better distribution of light also caused CO(,2) exchange on a leaf area basis to be greater in that canopy. Furthermore, greater CWFR was observed over the narrow-leafed isoline. Turbulent mixing was greater over the normal isoline when both canopies were fully-developed.
Subject Area
Agricultural engineering
Recommended Citation
BALDOCCHI, DENNIS DAVID, "MASS AND ENERGY EXCHANGES OF SOYBEANS: MICROCLIMATE-PLANT ARCHITECTURE INTERACTIONS" (1982). ETD collection for University of Nebraska-Lincoln. AAI8228144.
https://digitalcommons.unl.edu/dissertations/AAI8228144