NO. 15 AERIAL FERTILIZATION OF WHEAT JOHNSTON 7 



the carbon-dioxide-treated plants over both controls. The number 

 and weight of heads per plant are also greater. However, the weight 

 per head and the number of grains per plant are less in the carbon- 

 dioxide-treated plot. The large increase in total weight is due to the 

 weight of straw. Although the weight per grain of the plants on the 

 carbon-dioxide-treated plot was somewhat greater than those of the 

 two control plots, the number of grains per head was much less. This 

 experiment likewise indicates the accelerating efifect of carbon-dioxide 

 aerial fertilization on vegetative growth and an apparent depressing- 

 effect on grain production. 



During the following summer the plot experiment was repeated 

 with one additional treatment. It was thought that if phosphorus and 

 potassium fertilizers were added to one of the carbon-dioxide-treated 

 plots at time of heading, these plants might be improved with respect 

 to their grain production. The general procedure in this experiment 

 was similar to that of the previous year. However, the rate of air 

 fiow was increased to about 5 liters a minute, and the enclosed control 

 plot was changed to the east end of the row. The appearance of the 

 plants when harvested is shown in plate 6, and the data are sum- 

 marized in table 4. 



Table 4. — Smninary of 1033 Experiment with J}' heat Grown in 2 x 2-foot Plots 



Data 



Average CO2 concentration 

 (relative to normal air) .... 

 Number of stalks harvested... 

 Total weight (grams) at harvest 

 Total weight after air drying. . 

 Weight of water lost in drying. 



Number of heads 



Dry weight of heads 



Dry weight per head 



Dry weight of straw 



Dry weight of grain 



Number of grains 



Dry weight per grain 



Number of grains per head . . . 



Each plot was planted to '/2 grains of wheat, two to the hill, during 

 the first week of April. By April 26 the plants showed a fair start. 

 The glass sides, 60 inches high, were placed around plots i, 2, and 3, 

 and the carbon-dioxide mixture turned into plots 2 and 3 on April 29. 

 The average carbon-dioxide analyses showed the concentration in plot 

 2 to be somewhat greater than that of plot 3, the one to which phos- 

 phorus and potassium fertilizers were added. This fertilizer combina- 



