| Popis: |
During 1971 measurements were made of meteorological and biological variables above and within a wheat crop grown at Rutherglen in northeast Victoria. In the present paper a brief description is given of the apparatus used to measure carbon dioxide concentration gradients and absolute concentrations above the crop, together with a summary of the observations. The vertical CO 2 gradient was found to show little variation across the crop, confirming the assumption of horizontal homogeneity generally made in micrometeorological studies. Daytime differences in the CO 2 concentration between 2 and 1 m above the crop were generally steady at about 2 p.p.m., with nocturnal differences being more variable, of reversed sign and about 10 times greater in magnitude. The magnitudes of both daytime and nighttime differences increased through the season until the time of maximum crop growth, after which they decreased. At night vertical CO 2 differences were observed to oscillate in magnitude when wind velocities were less than approximately 1 m/sec, becoming generally larger when Richardson number exceeded a value of between 0.1 and 1. The CO 2 concentration at 2 m above the crop was found to be fairly constant during the daylight hours on single days or from day-to-day throughout the growing season ranging from about 310 to 320 p.p.m. Nocturnal values were more variable and were between 10 and 200 p.p.m. higher than the daytime values. |
