INVESTIGATIONS ON THE PRODUCTION OF PLANT FOOD, igr 



mined simultaneously with nitrates, and the curves show a marked 

 similarity except that the increases in nitrate came later. Thus 



1 1 I i | 1 I I I \ L_i 



Oct. Nov Dec Jan Feb Mar Apr May June July Aug Sspt 

 sen leu ' ° iste 



Fig. 62. — Amounts of Carbon Dioxide in Soil Air, and of Nitrate in 

 Soil at Different Seasons of the Year. 



we may conclude that the curves both for nitrate and carbon dioxide 

 are in the main production curves (fig. 64). 



o 2 



