FOOD FOR PLANTS 179 



Data presented heretofore, and which are con- 

 firmed by results hereafter to be presented, show 

 that of the four materials, Nitrate of Soda is most 

 effective in crop production, that is, the crop is able 

 to utilize or win back a larger percentage of nitrogen 

 in this form than in any of the other forms. With a 

 given amount of nitrogen, therefore, the crop yield 

 can be better maintained over a period of years by 

 the use of nitrogen in the form of Nitrate of Soda 

 than in the other forms, provided the soil is one that 

 does not allow rapid leaching. 



This apparently is what has happened in this case. 

 With the gradual exhaustion of soil nitrogen, which 

 was made available by the use of lime, and the failure 

 of the ammonium sulfate, blood and manure to give 

 back in the form of crops as large a proportion of the 

 applied nitrogen as the Nitrate of Soda, the yields 

 with the former became gradually less. 



The fact that cylinder 4B gave the largest average 

 yield through 20 years must not be taken as mean- 

 ing that the treatment given this cylinder is neces- 

 sarily the best or most effective. It will be remem- 

 bered that this cylinder receives cow manure at the 

 rate of 16 tons per acre annually, the cost of which 

 would be much in excess of the cost of 320 pounds of 

 Nitrate of Soda or its equivalent in ammonium sulfate 

 or dried blood, and therefore the larger yield does not 

 necessarily mean an efficient use of the applied nitro- 

 gen. As a matter of fact, the work shows this to be 

 the least efficient of the four forms. 



