Eddy correlation equipment was used to measure mass and energy fluxes over a soybean crop. A rapid response CO2 sensor, a drag anemometer, a Lyman-alpha hygrometer and a fine wire thermocouple were used to sense the fluctuating quantities.
Diurnal fluxes of sensible heat, latent heat and CO2 were calculated from these data. Energy budget closure was obtained by summing the sensible and latent heat fluxes determined by eddy correlation which balanced the sum of net radiation and soil heat flux. Peak daytime CO2 fluxes were near 1.0 mg m−2 (ground area) s−1.
The eddy correlation technique was also employed in this study to measure nocturnal CO2 fluxes caused by respiration from plants, soil, and roots. These CO2 fluxes ranged from - 0.1 to - 0.25 mg m−2s−1.
From the data collected over mature soybeans, a relationship between CO2 flux and photosynthetically active radiation (PAR) was developed. The crop did not appear to be light-saturated at PAR flux densities < 1800 ΜEi m−2 s−1. The light compensation point was found to be about 160 ΜEi m−2 s−1.
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Published as Paper No. 7402, Journal Series, Nebraska Agricultural Experiment Station. The work reported here was conducted under Nebraska Agricultural Experiment Station Project 27-003 and Regional Research Project 11–33.
Post-doctoral Research Associate, Professor and Professor, respectively. Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0728.
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Anderson, D.E., Verma, S.B. & Rosenberg, N.J. Eddy correlation measurements of CO2, latent heat, and sensible heat fluxes over a crop surface. Boundary-Layer Meteorol 29, 263–272 (1984). https://doi.org/10.1007/BF00119792