FOOD FOR PLANTS 177 



Cylinder 17B, ammonium sulfate, equivalent to 320 pounds 

 of Nitrate of Soda per acre. 



Cylinder 18B, dried blood, equivalent to 320 pounds of 

 Nitrate of Soda per acre. 



Thus a careful record is kept of the amount of 

 nitrogen applied each year and of the yield of dry 

 matter from each cylinder. From determinations of 

 the amount of nitrogen in the dry matter the total 

 amount of nitrogen removed by the crop each year 

 is easily calculated. 



Yield of Dry Matter. 



The yield of dry matter under the four different 

 treatments for the 20 years is shown in table 1, aver- 

 ages being given for two 10-year periods and also 

 for the entire 20 years. For each 10-year period the 

 yield has been largest with the manure, though it is 

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

 which would indicate that with manure at the rate 

 of 16 tons per acre the fertility of the soil is not being 

 fully maintained. The lowest yield is from 18B 

 where dried blood is used as the source of nitrogen. 

 Here again the average yield is less for the second 

 10-year period than for the first. For plots 8B and 

 17B, which receive Nitrate of Soda and ammonium 

 sulfate, respectively, the average yields for the first 

 10 years are essentially the same for the two treat- 

 ments, but for the second 10 years the average for 

 the Nitrate of Soda treatment is considerably above 

 that for the ammonium sulfate; furthermore, the 

 average yield with ammonium sulfate is, like the 

 yield with dried blood and farm manure, less for the 



