Measurement and interpretation of carbon dioxide fluxes in the field.

Abstract

The DM production of field crops can be estimated from their net uptake of CO₂, and vertical profiles of CO₂ concentration show that crop plants normally assimilate CO₂ both from the atmosphere and from the soil. The atmospheric component can be estimated from the CO₂-concentration at two heights and the wind speed at three heights above the crop, and the soil component by direct absorption in soda lime. Measurements over grass and field beans at Rothamsted gave a soil CO₂-production of about 0.03 mg/cm²/hr and maximum gross rates of photosynthesis about 0.2 mg CO₂/cm²/hr. In terms of total solar radiation (wavelength range 0.3-2 mu ), the efficiency of photosynthesis varied from about 1% in bright sunshine to 2% or more with cloud, agreeing well with measurements on selected plants in the laboratory. An attempt to establish the complete CO₂-balance for beans emphasized the importance of respiratory flux in determining DM production. Conventionally assumed respiration rates are inadequate and field measurements are urgently needed. F. s.-R.B. (Abstract retrieved from CAB Abstracts by CABI’s permission)