Carbon dioxide, water vapor and sensible heat exchanges of a grain sorghum canopy

✍ Scribed by Dean E. Anderson; Shashi B. Verma

• Publisher: Springer
• Year: 1986
• Tongue: English
• Weight: 763 KB
• Volume: 34
• Category: Article
• ISSN: 0006-8314
• DOI: 10.1007/bf00120986

✦ Synopsis

With the aid of eddy correlation instrumentation, the components of the energy budget and CO, flux were measured over grain sorghum grown at Mead, Nebraska. Diurnal patterns of sensible heat, latent heat, CO2 and momentum flux are examined for typical days. On a mostly clear day when the crop leaf area index was 3.7, net radiation reached a mid-day peak of 560 W m -*, while sensible and latent heat fluxes peaked at 50 and 460 W m -*, respectively. The peak CO1 flux occurring just prior to solar noon was 1.5 mg m -*(ground area) s -'. CO, flux (respiration from plants, soil and roots) in the early evening was about -0.28 mg m ' (ground area) s -'.

A relationship between CO, flux and photosynthetically active radiation (PAR) was developed. Except during the late stage of growth (growth stage = 8.5, toward the initiation of senescence), the crop showed no evidence of saturation up to PAR x 1800 pEi m -' s -', The light compensation point was found to be about 211 pEi me2 s '. Examination of CO, flux-PAR relationships for selected days through the season indicated an aging effect in terms of a decrease in photosynthetic activity of the sorghum canopy. Measurements made on two consecutive days demonstrate the effects of weather conditions on CO, flux and carbon-water flux ratio (a measure of water use efficiency of the crop). The occurrence of regional sensible heat advection with concommitant high vapor pressure deficit and air temperature-limited CO, exchange reduced the carbon-water flux ratio.