1905.] PUBLIC DOCUMENT — No. 33. 123 



it still maintains its superiority as compared with the other 

 fertilizers furnishing nitrogen. The barnyard manure pro- 

 duces a superior crop, not, it is believed, because of the 

 superior availability of the nitrogen it contains, but, as has 

 been suggested, because of the better physical condition of 

 the soil produced by the humus it furnishes. 



If we compare the diiferent materials used as sources of 

 nitrogen on the basis of increase in crop rather than on the 

 basis of total product, they rank to date for the entire period 

 of the experiment 1890 to 1904 as follows : — 



liclativc Increases in Yields (^Avcnujc for the Fifteen Years) . 



Per Cent. 



Nitrate of soda, 100.00 



Barnyard manure, ....... 88.60 



Dried blood, 66.90 



Sulfate of ammonia, ...... 59.90 



These figures make the superiority of nitrate of soda as a 

 source of fertilizer nitrogen very ap})arent. In view of the 

 fact that at current prices it furnishes a pound of nitrogen at 

 a lower cost than almost any other material, the advisability 

 of depending chiefly ui>on the nitrate as a means of supply- 

 ing the important element nitrogen becomes strikingly evi- 

 dent. 



Effect of a Leyume vj)on. the FoUnirhvi Crop. 

 It is pointed out, in introducing what will be said under 

 this topic, that the object in this experiment is not to test 

 the efi'ect of producing a legume which is plowed under, but 

 simply the improvement, if any, derived from the roots and 

 stubble the legume leaves behind Avhen harvested. The 

 results thus far indicate little improvement in the condition 

 of the soil following the culture of the soy bean, with iha 

 exception of those obtained with the potato crop following 

 soy beans in 1902. The introduction of the clover crop, on 

 the other hand, was followed by marked improvement ; and 

 it would now appear possible that the good results with the 

 potato crop in 1 902 may have been in part at least a conse- 

 quence of the unexhausted residue of i\\Q clover stubble and 

 roots turned under in the spring of 1900. The following 

 table, with th<' curve below it, makes the facts clear : — 



