FOOD FOR PLANTS 185 



gen or both. The loss cannot all be attributed to a 

 leaching out of the materials, even though the nitrifi- 

 cation of ammonia 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 somev^hat larger 

 yields than Nitrate of Soda, but the increased yields 

 v^^ere not sufficient to justify the increase in the cost 

 of nitrogen. 



Furthermore, the average yield v^ith the manure 

 vv^as 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 annually, the crop yield is not being main- 

 tained, while with Nitrate of Soda at the rate of 320 

 pounds per acre annually 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 with the nitrate than with any of the 

 other materials, the 20-year average being as follows : 



Per cent. 



Nitrate o£ 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 10-year period, whereas the average 

 recovery 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 with the crop yields, and in- 



