Line Source Carbon Dioxide Release. I. Field Experiment
1974
Allen, L. H. | Desjardins, R. L. | Lemon, E. R.
Carbon dioxide gas was released from one northeastsouthwest line in a corn (Zea mays L.) field during several days in August and September, 1969. CO₂ concentration profiles were measured at 15 and 45 m downwind. The purposes of the releases were: (1) to study the micrometeorological transport processes in plant canopies using CO₂, as a tracer, and (2) to determine the micrometeorological feasibility of CO₂ enrichment under field conditions. The study showed that vertical turbulent diffusion and horizontal mass flow quickly diminished the concentration of CO₂, downwind from the line source. High concentrations of CO₂ could be maintained in the canopy only under a stable temperature stratification of the air which reduced vertical wind fluctuations. Short-term eddies with CO₂ concentrations in excess of 1,000 ppm were observed 30 m downwind from the release line at an analyzer height of 530 cm, but these were very infrequent. CO₂ concentration profiles showed that CO₂ tended to be turbulently diffused upward and wafted downwind, with some of the CO₂ being again transported into the canopy. Turbulent diffusion in the canopy was usually too active to maintain a high CO₂ concentration; however, this same effectiveness of turbulence assures an adequate supply of CO₂ to plant canopies under typical field conditions. This study showed, from a micrometeorological viewpoint, that CO₂ enrichment would not be practical under most natural field and crop conditions because of rapid gaseous exchange with the bulk atmosphere.
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