y2 CYANAMID — MANUFACTURE^ CHEMISTRY AND USES 



gen, the increased yield is almost proportional to the amount 

 of nitrogen applied, but the rate of increase drops off rapidly 

 until a point is reached where further applications not only 

 do not increase the yield but tend to decrease it. If too much 

 fertilizer is applied the plant may even be killed. The "burn- 

 ing" and occasional destruction of vegetation by excessive 

 applications of fertilizer salts is well known to agriculturists. 

 A similar phenomenon has been investigated by Headden and 

 Sackett^ in Colorado, where it was shown that the formation 

 of excessive quantities of nitrates has caused in some cases 

 the total destruction of all plant life, often over areas miles 

 in extent. 



Toxicity, therefore, is a question of the amount of fertilizer 

 applied. All of the common, nitrogenous, mineral fertilizers 

 may have a toxic action if too much is used, but with the 

 ordinary applications of practical agriculture none of these 

 materials is toxic. Experience has determined the maximum 

 quantities of nitrogen that can be economically utilized by the 

 various crops under various soil conditions, and the possible 

 effects of larger quantities than this maximum economical 

 quantity in each case have little interest to the practical farmer. 

 Cotton, corn, wheat, oats, and similar crops seldom economically 

 utilize more than 15 to 25 pounds of nitrogen per acre. Sugar 

 beets and sugar cane may utilize as high as 40 to 50 pounds. 

 Potatoes, truck crops, some fruits, and tobacco may utilize as 

 high as 60 to 70 pounds of nitrogen per acre. With such 

 applications it is doubtful if any of the mineral fertilizers in 

 question would exert a toxic action on the plant, even if they 

 were applied alone, provided the time and method of applica- 

 tion were suitable. 



As a matter of fact, however, when large applications of 



nitrogen are desired, it is customary to mix several kinds of 



nitrogenous materials together and to apply the mixture in 



several portions, instead of all at one time. Moreover, agri- 



^ Colorado Exp. Sta. Bulletin 179, 191 1. 



