Within well-developed crop canopy, which may hinder air currents, lus grave (reviewed by Newman 1963) reported rather violent reductions from 300 ppm value for CO2, especially during calm early morning hours. CO2 vels according to the rate of photosynthesis during a low level or fluctuated mplete lack of turbulence and changes in a crop canopy to promote air rbulence may be useful in replenishing Co2 levels. Strong hot winds may be trimental in causing increased water losses and may not be as effective in areasing carbon dioxide within a crop canopy which results in more rbulent air currents.
Generally, field crops are more productive when protected by a windbreak agley and Gowen 1960; Rosenberg 1966a and b); but yield increases were ributed to increased relative humidity and increased average air and soil nperature, due to reduced windspeed, although CO2 levels were not asured in these studies. Windbreaks reduced wind speeds 50 to 70% within a tance of eight times the height of the windbreak (Bagley and Gowen 1960). nilar results were obtained by Rosenberg (1966b), but he indicated that the