CONCENTRATION OF CO2IN THE AIR ABOVE A SUGAR BEET FIELD*

The concentration of CO, in air sampled above a sugar beet crop was measured during July, August, and early September 1966 at Scottsbluff, Nebr. During July the mean daytime concentration decreased from 310 ppm to 283 ppm as the leaf area index increased from 0.8 to 4.0. Only small deviations from the mean daytime Concentration of 283 ppm occurred during the remainder of the season. The mean nocturnal concentration during this period was 320 ppm and was more variable than the daytime concentration. The daily amplitude of concentration averaged 70 ppm and was as great at times as 100 ppm. Regression analysis revealed strong negative correlation between COZ concentration and mean wind speed during the night. Mean concentration was independent of mean temperature, mean incident radiation, and predominant wind direction. During each day the concentration remained constant between 1% hr after sunrise and 1 hr before sunset except for a few cases. These were associated with incident radiation below 0.2 cal cm-2 min-1 and/or wind speeds at 25 cm above the crop of less than 0.3 m sec-l or more than 3 m sec-I. Evidence is presented that the concentrations reported here are at least partially dependent on the flux to and from the sugar beet crop.