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Agronomy Journal Abstract -

Carbon Dioxide Uptake by Wide-Row Grain Sorghum Computed by the Profile Bowen Ratio1


This article in AJ

  1. Vol. 66 No. 1, p. 35-41

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  1. L. H. Allen Jr.,
  2. R. J. Hanks,
  3. J. K. Aase and
  4. H. R. Gardner2



A method for computing CO2 uptake by an irrigated crop of wide-row grain sorghum (Sorghum bicolor (L.) Moench, var. ‘RS-610’) was devised from measured profiles of temperature, water vapor, and CO2 over the crop. The crop Bowen ratio, β and the ratio of photochemical heat flux density of carbon dioxide fixation to latent heat flux density, α, were determined from profiles of points, rather than from just two points. We call this method the profile Bowen ratio. The parameters α and β were used with the energy balance equation to compute the flux density of CO2 to the crop as a function of solar radiation, which itself was a function of time of day. CO2 flux density plotted as a function of solar radiation (or time of day) was lower at the highest radiation loads (midday) than at 1000 or 1400 hours. The lower CO2 flux density at midday may be the result of more mutual leaf shading in this crop geometry at high solar elevation angles. The CO2 flux density curve also showed concave curvature at the radiation loads concomitant with early morning and late afternoon hours when much of the solar energy was penetrating to ground in this east-west row crop. Finally, computed daily CO2 fluxes were reasonably close to the CO2 equivalent of dry matter accumulation rates plus estimated respiration.

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