IGO Food for Plants. 



loss cannot all be attrilmted to a leaching out of the 

 materials, even though the nitrification of anmionia and 

 organic residues may go on throughout a large portion 

 of the year. 



In the above-mentioned rotation cow manure at the 

 rate of 16 tons per acre gave somewhat larger yields 

 than nitrate of soda, but the increased yields were not 

 sufficient to justify the increase in the cost of nitrogen. 



Furthermore, the average yield mth the manure was 

 less for the second 10-year period than for the first, 

 while the reverse is true with the nitrate of soda. Thus 

 it is shown that with 16 tons of manure per acre annu- 

 ally, the crop yield is not being maintained, while with 

 nitrate of soda at the rate of 320 pounds per acre annu- 

 ally it is increasing slightly, as shown by the average 

 for the second 10-year period. 



The percentage of nitrogen recovered in the crop was 

 greater Mith the nitrate than with any of the other 

 materials, the 20-year average being as follows: 



Per cent. 



Nitrate of Soda 62.42 



Ammonium sulfate 47 . 48 



Dried blood 38.69 



Cow manure 32 . 69 



The average recovery with nitrate for the second 10- 

 year period was 64.35 per cent, as against 60.48 per cent 

 for the first lO^year period, whereas the average re- 

 coveiy with the ammonium sulfate, dried blood and 

 manure was all less for the second 10-year period than 

 for the first. 



This is in agreement vnih the crop fields, and indi- 

 cates a diminishing efficiency for the ammonivmi sulfate, 

 blood and manure, and a gradual increase in efficiency 

 for the nitrate of soda. 



The work shows that when properly used nitrate of 

 soda alone as a source of nitrogen may be depended 

 upon to maintain crop yields over a long period, and 

 that a given amount of nitrogen in this form is more 

 effective than an equivalent amount in the form of am- 

 monium sulfate, or organic materials. 



