AERIAL FERTILIZATION OF WHEAT PLANTS WITH 

 CARBON-DIOXIDE GAS 



By earl S. JOHNSTON 

 Diznsion of Radiation and Organisms, Smithsonian Institution 



(With Six Plates) 

 INTRODUCTION 



Experiments on the carbon-dioxide assimilation of yomig wheat 

 plants reported by Hoover, Johnston, and Brackett (j) ^ covered a 

 wide range of light intensities and carbon-dioxide concentrations. 

 Under the artificially controlled conditions used, it was shown that 

 there was a linear variation of carbon-dioxide assimilation with 

 carbon-dioxide concentration in the presence of excess light over a 

 limited range. With the maximum light intensity, approximately one- 

 fourth that of sunlight on a cloudless summer day in Washington, 

 carbon dioxide became a limiting factor at a concentration of about 

 that of nojmal air. Since sunlight intensity for a number of hours 

 per clear day is much higher than the highest intensity employed in 

 these experiments, it was thought that interesting and important data 

 might be obtained from experiments conducted with sunlight under 

 more natural conditions out of doors and with the carbon-dioxide 

 concentration surrounding the plants some 3 to 4 times that of normal 

 air. 



It is not feasible here to make an extended review of the large 

 amount of work covering the subject of aerial fertilization of plants 

 with carbon dioxide. Many experimenters report beneficial effects. 

 Several sources of carbon dioxide have been utilized, including carbon- 

 dioxide generators, commercial tanks of the compressed gas, scrubbed 

 fiue gas, and that arising from animal and plant manures. Both green- 

 house and field experiments have been tried. Carbon dioxide from 

 blast furnaces, after being freed of matter injurious to plants and 

 piped to fields where it was allowed to spread over extended areas, 

 caused marked improvement in crop yields. Because of the difficulty 

 of confining the gas over such large areas in open fields, aerial fertili- 

 zation with carbon dioxide is better adapted to greenhouse work. 



Relatively little work on increasing the products of photosynthesis 

 by enriching the air with carbon dioxide has been done in this 



Italic numbers in parentheses refer to list of references at end of paper. 

 Smithsonian Miscellaneous Collections, Vol. 94, No. 15 



